Ultrasonography for confirmation of gastric tube placement

Abstract

Background

Gastric tubes are commonly used for the administration of drugs and tube feeding for people who are unable to swallow. Feeding via a tube misplaced in the trachea can result in severe pneumonia. Therefore, the confirmation of tube placement in the stomach after tube insertion is important. Recent studies have reported that ultrasonography provides good diagnostic accuracy estimates in the confirmation of appropriate tube placement. Hence, ultrasound could provide a promising alternative to X‐rays in the confirmation of tube placement, especially in settings where X‐ray facilities are unavailable or difficult to access.

Objectives

To assess the diagnostic accuracy of ultrasound alone or in combination with other methods for gastric tube placement confirmation in children and adults.

Search methods

This systematic review is an update of a previously published Cochrane review.

For this update, we searched the Cochrane Library (2021, Issue 6), MEDLINE (to April 2023), Embase (to April 2023), five other databases (to July 2021), and reference lists of articles, and contacted study authors.

Selection criteria

We included studies that evaluated the diagnostic accuracy of naso‐ and orogastric tube placement confirmed by ultrasound visualization using X‐ray visualization as the reference standard. We included cross‐sectional studies and case‐control studies. We excluded case series or case reports. We excluded studies if X‐ray visualization was not the reference standard or if the tube being placed was a gastrostomy or enteric tube.

Data collection and analysis

Two review authors independently assessed the methodological quality and extracted data from each of the included studies. We contacted the authors of the included studies to obtain missing data. There were sparse data for specificity. Therefore, we performed a meta‐analysis of only sensitivity using a univariate random‐effects logistic regression model to combine data from studies that used the same method and echo window.

Main results

We identified 12 new studies in addition to 10 studies included in the earlier version of this review, totalling 1939 participants and 1944 tube insertions.

Overall, we judged the risk of bias in the included studies as low or unclear. No study was at low risk of bias or low concern for applicability in every QUADAS‐2 domain.

There were limited data (152 participants) for misplacement detection (specificity) due to the low incidence of misplacement. The summary sensitivity of ultrasound on neck and abdomen echo windows were 0.96 (95% confidence interval (CI) 0.92 to 0.98; moderate‐certainty evidence) for air injection and 0.98 (95% CI 0.83 to 1.00; moderate‐certainty evidence) for saline injection. The summary sensitivity of ultrasound on abdomen echo window was 0.96 (95% CI 0.65 to 1.00; very low‐certainty evidence) for air injection and 0.97 (95% CI 0.95 to 0.99; moderate‐certainty evidence) for procedures without injection. The certainty of evidence for specificity across all methods was very low due to the very small sample size. For settings where X‐ray was not readily available and participants underwent gastric tube insertion for drainage (8 studies, 552 participants), sensitivity estimates of ultrasound in combination with other confirmatory tests ranged from 0.86 to 0.98 and specificity estimates of 1.00 with wide CIs.

For studies of ultrasound alone (9 studies, 782 participants), sensitivity estimates ranged from 0.77 to 0.98 and specificity estimates were 1.00 with wide CIs or not estimable due to no occurrence of misplacement.

Authors' conclusions

Of 22 studies that assessed the diagnostic accuracy of gastric tube placement, few studies had a low risk of bias. Based on limited evidence, ultrasound does not have sufficient accuracy as a single test to confirm gastric tube placement. However, in settings where X‐ray is not readily available, ultrasound may be useful to detect misplaced gastric tubes. Larger studies are needed to determine the possibility of adverse events when ultrasound is used to confirm tube placement.

Plain language summary

Is ultrasound alone or in combination with other methods useful for confirmation of gastric tube placement?

Key messages

– Whether ultrasound offers a promising alternative to X‐rays for confirming proper gastric tube placement is uncertain.

– More research is needed to determine the accuracy of ultrasound to identify misplaced tubes.

What are gastric tubes and why are they used?

The oesophagus (food pipe) is a muscular tube that connects the mouth to the stomach. If a person cannot swallow properly, a gastric tube may be inserted through the nose or the mouth to provide medicines or liquid food directly into the stomach. Care is needed though, as the oesophagus is very close to the trachea (wind pipe), which allows air to travel to the lungs. If the gastric tube is misplaced and food or medicines passed into the trachea, it can result in a severe infection in the lungs (called pneumonia) or other complications. Therefore, the confirmation of tube placement in the stomach after tube insertion is important. Correct placement is usually checked using X‐rays.

Why is replacing X‐rays with ultrasound for confirming gastric tube placement important?

Ultrasound is a diagnostic imaging technique that uses sound waves to create images of the inside of the body. It could be more accessible and convenient than X‐rays, especially in locations with limited resources.

What did we want to find out?

We wanted to determine the accuracy of ultrasound in confirming gastric tube placement and assess its potential to replace X‐rays as the standard method.

What did we do?

We analyzed 22 studies with 1939 participants looking at the accuracy of ultrasound for confirming gastric tube placement.

Study findings

Most studies showed that ultrasound performed well in confirming correct tube placement, but there were limited data on incorrect tube placements and potential complications as only 152 participants in the studies had a misplaced tube.

The studies used three ultrasound methods: neck approach, upper abdominal approach, and a combination of both.

Ultrasound alone was not sufficient for confirming proper placement for feeding tubes but, when combined with other tests, it could be useful for confirming gastric drainage tubes.

What are the limitations of the evidence?

Many studies had poor or unclear methods, so our confidence in the evidence was reduced.

Only eight of the 22 studies were considered representative of people who usually need a gastric tube.

Results varied for incorrect tube placement.

Future research

Larger studies are needed to determine if ultrasound can replace X‐rays for confirming gastric tube placement and whether it can help reduce complications from misplaced tubes.

How up to date is this evidence?

This review updates our previous review. The evidence is up to date to April 2023.

Summary of findings

Summary of findings 1. Diagnostic accuracy of ultrasonography with air injection on neck and abdomen echo windows used to diagnose gastric tube placement in adults and children.

Diagnostic accuracy of ultrasonography with air injection on neck and abdomen echo windows used to diagnose gastric tube placement in adults and children
Patient or population: adults and children Setting: any setting New test: ultrasonography with air injection on neck and abdomen echo windows Reference test: X‐ray; threshold: any threshold used in the original studies Summary sensitivity: 0.96 (95% CI 0.92 to 0.98); specificity: range: 1.0 to 1.0
Test result	Number of results per 1000 participants tested (95% CI)			Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Prevalence 80%	Prevalence 90%	Prevalence 95%
True positives	768 (736 to 784)	864 (828 to 882)	912 (874 to 931)	179 (3)	⊕⊕⊕⊝ Moderatea	—
False negatives	32 (16 to 64)	36 (18 to 72)	38 (19 to 76)
True negatives	See comments			9 (3)	⊕⊝⊝⊝ Very lowa,b	3 studies, involving 9 participants, reported specificity values ranging from 1.0 to 1.0 in identifying true negatives and false positives.
False positives
CI: confidence interval.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

^a Downgraded one level due to high or unclear risk of bias in the patient selection domain.
^b Downgraded two levels due to a very small sample size.

Summary of findings 2. Diagnostic accuracy of ultrasonography with saline injection on neck and abdomen echo windows used to diagnose gastric tube placement in adults and children?

Diagnostic accuracy of ultrasonography with saline injection on neck and abdomen echo windows used to diagnose gastric tube placement in adults and children?
Patient or population: adults and children Setting: any setting New test: ultrasonography with saline injection on neck and abdomen echo windows Reference test: X‐ray; threshold: any threshold used in the original studies Summary sensitivity: 0.98 (95% CI 0.83 to 1.00); specificity: 0.84 (range: 0.65 to 1.0)
Test result	Number of results per 1000 participants tested (95% CI)			Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Prevalence 80%	Prevalence 90%	Prevalence 95%
True positives	787 (666 to 799)	885 (750 to 899)	934 (791 to 949)	226 (4)	⊕⊕⊕⊝ Moderatea	—
False negatives	13 (1 to 134)	15 (1 to 150)	16 (1 to 159)
True negatives	See comments			5 (2)	⊕⊝⊝⊝ Very lowa,b	2 studies, involving 5 participants, reported specificity values ranging from 0.67 to 1.0 in identifying true negatives and false positives.
False positives
CI: confidence interval.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

^a Downgraded one level due to high or unclear risk of bias in the patient selection domain.
^b Downgraded two levels due to very small sample size.

Summary of findings 3. Diagnostic accuracy of ultrasonography with air injection on abdomen echo window used to diagnose gastric tube placement in adults and children?

Diagnostic accuracy of ultrasonography with air injection on abdomen echo window be used to diagnose gastric tube placement in adults and children?
Patient or population: adults and children Setting: any setting New test: ultrasonography with air injection on abdomen echo window Reference test: X‐ray; threshold: any threshold used in the original studies Summary sensitivity: 0.96 (95% CI 0.65 to 1.00); specificity: range: 0.80 to 1.0
Test result	Number of results per 1000 participants tested (95% CI)			Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Prevalence 80%	Prevalence 90%	Prevalence 95%
True positives	768 (520 to 800)	864 (585 to 900)	912 (618 to 950)	557 (3)	⊕⊝⊝⊝ Very lowa,b,c	—
False negatives	32 (0 to 280)	36 (0 to 315)	38 (0 to 332)
True negatives	See comments			89 (3)	⊕⊕⊝⊝ Lowa,d	3 studies, involving 89 participants, reported specificity values ranging from 0.80 to 1.0 in identifying true negatives and false positives.
False positives
CI: confidence interval.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

^a Downgraded one level due to high or unclear risk of bias in the patient selection domain.
^b Downgraded one level due to wide confidence intervals.
^c Downgraded one level due to unexplained heterogeneity across studies.
^d Downgraded one level due to small sample size.

Summary of findings 4. Diagnostic accuracy of ultrasonography without any injection on abdomen echo window used to diagnose gastric tube placement in adults and children?

Diagnostic accuracy of ultrasonography without any injection on abdomen echo window used to diagnose gastric tube placement in adults and children?
Patient or population: adults and children Setting: any setting New test: ultrasonography without any injection on abdomen echo window Reference test: X‐ray; threshold: any threshold used in the original studies Summary sensitivity: 0.97 (95% CI 0.95 to 0.99); specificity: range: 1.0 to 1.0
Test result	Number of results per 1000 participants tested (95% CI)			Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Prevalence 80%	Prevalence 90%	Prevalence 95%
True positives	776 (760 to 792)	873 (855 to 881)	922 (903 to 941)	340 (4)	⊕⊕⊕⊝ Moderatea	—
False negatives	23 (8 to 40)	27 (19 to 45)	28 (9 to 47)
True negatives	See comments			14 (2)	⊕⊝⊝⊝ Very lowa,b	2 studies, involving 14 participants, reported specificity values ranging from 1.0 to 1.0 in identifying true negatives and false positives.
False positives
CI: confidence interval.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

^a Downgraded one level due to high or unclear risk of bias in the patient selection domain.
^b Downgraded two levels due to very small sample size.

Background

Gastric tubes are commonly used for the administration of drugs and delivery of nutrition directly into the gastrointestinal tract (enteral feeding) for people who are unable to swallow (e.g. people after stroke, or who need respirator support) (NICE 2006; Samuels 2013). They are also employed in diverse care settings to provide adequate nutrition and hydration to people of all ages who are unable to ingest or absorb sufficient nutrients. Placement of a gastric tube is performed by inserting the tube through the nose (nasogastric tube) or mouth (oral gastric or orogastric tube), down the oesophagus, and into the stomach (ENA 2015; Samuels 2013). Generally, doctors or nurses insert the tubes blindly at the bedside by pushing the tube into the nose or mouth. This review focused on nasogastric and orogastric tubes.

In Europe, approximately 10 million nasogastric feeding tubes are used annually due to an increase in the number of hospitalized patients, with one million in the UK (Torsy 2020). According to data from the USA, 1.2 million nasogastric feeding tubes are inserted each year (Metheny 1999; Bloom 2022). Gastric tubes are also used for the decompression of the gastrointestinal tract after the application of a bag valve mask, which is mainly used in resuscitation (Chenaitia 2012). Gastric tubes, made primarily from flexible polyurethane, and sometimes latex, silicone, or polyurethane, require regular replacement if used for extended periods (Samuels 2013). In addition, tubes sometimes require unscheduled replacement due to dislodgement caused by vomiting or blockages (Thomson 2000). Gastric feeding tubes are associated with the recognised risk of misplacement into the trachea (airway) through the larynx due to the proximity of the larynx to the oesophagus. During insertion, the tubes might enter the trachea through the larynx. Feeding via a misplaced tube that goes undetected in the respiratory tract can result in severe pneumonia, pneumothorax, empyema, and pulmonary haemorrhage. Therefore, it is crucial to verify the correct placement of the tube before introducing feeds or medications (Kawati 2005). Recommended methods to confirm correct tube placement are X‐ray visualization and suction of gastric fluids, including pH test (Boullata 2017). In a prehospital situation, a combination of the suction method and auscultation (listening to the internal sounds of the body using a stethoscope) is used (Chenaitia 2012).

Medical ultrasound is one of the diagnostic imaging techniques using ultrasound waves. Studies have demonstrated that ultrasonography provides good diagnostic accuracy estimates in the confirmation of appropriate tube placement (Brun 2014; Chenaitia 2012). These studies focused on tube placement for decompression of the stomach after the administration of a bag valve mask in a prehospital situation where X‐rays were not available. Therefore, ultrasound could provide a promising alternative to X‐rays in the confirmation of tube placement, especially in settings where X‐ray facilities are unavailable or difficult to use.

Target condition being diagnosed

Appropriate gastric tube placement for any reason.

Index test(s)

Ultrasound test for gastric tube confirmation that visualizes the tubes via both the neck and abdomen, regardless of frequency of ultrasound, probe shape (linear or convex), or probe size. The test is performed in both prone and sitting positions, and can also be performed at the bedside. Visualization of the tubes is generally from the neck, abdomen, or both. Direct visualization of tubes in the oesophagus and stomach is interpreted as correct placement. During visualization, saline or air flush of the tube may help to visualize it by showing dynamic fogging in the stomach (Kim 2012).

Clinical pathway

People may need a gastric tube for the administration of drugs, enteral feeding, or drainage. In these situations, the gastric tube is inserted via the nose or mouth, down the oesophagus, and into the stomach.

After the gastric tube is inserted, its location should be promptly confirmed before proceeding with feeding or drug administration (AACCN 2009). This is by suction of gastric fluids (visual inspection of aspirate contents and checking of pH) (AACCN 2009; Chenaitia 2012). Although the auscultation method (instillation of air in the tube with sounds heard simultaneously through a stethoscope placed over the stomach region) is not recommended, it is also performed as prior tests in clinical practice (Metheny 2019). Tube placement is usually confirmed by X‐ray visualization of the tube (e.g. chest X‐ray).

Ultrasound may be used as a replacement test for X‐ray. During the test, saline or air flush of the tube may help to visualize it.

In addition, if the person with the tube placement has vomited, retched, or coughed; if oropharyngeal suction was needed; or as a standard protocol, the tube will require checking every four hours during daily feeding or in cases of suspected tube dislodgement (Holland 2013).

The clinical pathway for gastric tube placement is described in Figure 1.

1.

Clinical pathway for gastric tube placement.

Prior test(s)

As a prior test, a tube aspirate for appearance and pH measurement is used. Clinicians may perform the auscultation method (instillation of air in the tube with sounds heard simultaneously through a stethoscope placed over the stomach region) as a prior test, but it is not considered reliable alone (Boullata 2017). In a prehospital situation, a combination of the suction and the auscultation method is possibly used (Chenaitia 2012). If one of these tests showed misplacement, reinsertion of the tube is needed.

Role of index test(s)

The role of ultrasound is assumed as a replacement test for X‐ray visualization. The downstream consequences according to the four test accuracy categories are as follows:

• no need for further testing for true positive = correct gastric tube placement and correct visualization by ultrasound;

• serious accidents of feeding via a tube misplaced in the trachea or no effective drainage of gastric contents via a tube misplaced in the trachea for false positive = incorrect gastric tube placement but not visualized by ultrasound;

• useless reinsertion of the tube and retesting for false negative = correct gastric tube placement but not visualized by ultrasound;

• safe feeding or effective drainage of gastric contents for true negative = incorrect gastric tube placement and correct visualization by ultrasound.

Alternative test(s)

X‐ray visualization is generally used to assess appropriate tube placement (Bourgault 2009). Although the risk of cancer from X‐rays is not conclusive, concerns regarding the risks associated with frequent exposure to X‐rays exist (Berrington 2004).

In addition, pH test of aspirate is used. The National Patient Safety Agency reported if pH is between 1 and 5.5, it is safe to start feeding (Lamont 2011; National Patient Safety Agency 2011). There is lack of consensus on the best pH cut‐point to make the distinction. However, if pH is between 5 and 6, checking of the pH with a competent colleague is recommended as misinterpretations of pH is possible (Lamont 2011).

Rationale

The use of ultrasonography to assess appropriate tube placement has the potential to reduce patient discomfort. Confirmation by X‐ray visualization can be difficult for people with tube placement because they have to change their body position to have a hard film plate placed on their back, or stand up for scanning while dealing with uncomfortable tubes hanging from their nose or mouth. An ultrasound test, by comparison, can be performed at the bedside without the need for the person to sit up or change position, and can, therefore, reduce the discomfort of the procedure for the patient (Vigneau 2005). In addition, obtaining results from an X‐ray examination can take several hours, which may cause delays in the use of the tube for administering feedings or medications (Taylor 2021).

Ultrasonography can also widen accessibility to confirmatory testing outside the hospital environment. As some ultrasound devices are portable, medical care providers who visit patients in the home can use ultrasound to check appropriate tube placement. Patients need not visit the hospital for insertion and confirmation of nasogastric or orogastric feeding tubes, which is an important consideration in the primary care setting (Mariani 2010).

The National Patient Safety Agency recommends that before using feeding tubes, repeated placement checks should be performed by X‐ray or pH of aspirate measured at least once daily (National Patient Safety Agency 2011). X‐rays should be avoided for children as much as possible due to concerns about the risk of irradiation (Frush 2003). Although the dose of irradiation by chest or abdominal X‐rays is small according to the linear non‐threshold model used in risk assumption, reducing irradiation as much as possible is of value to people of all ages (Berrington 2004; CNSC 2013).

We hypothesized that ultrasound could be a beneficial alternative to X‐ray visualization since ultrasound devices have become common not only in critical care but also in primary care or prehospital settings. This systematic review is an update of a previously published Cochrane review (Tsujimoto 2017).

Objectives

To assess the diagnostic accuracy of ultrasound alone or in combination with other methods for gastric tube placement confirmation in children and adults.

Secondary objectives

To assess the diagnostic accuracy of ultrasound for gastric tube placement confirmation in children (aged 16 years or less).

To investigate the potential sources of heterogeneity, we planned to assess the effects of the following factors on the diagnostic accuracy of ultrasound: body mass index, clinical setting (emergency setting or not), tube diameter, and echo window (the neck, abdomen, or both).

Methods

Criteria for considering studies for this review

Types of studies

We included studies that evaluated the diagnostic accuracy of naso‐ and orogastric tube placement confirmed by ultrasound visualization and using X‐ray visualization as the reference standard. We included cross‐sectional studies and case‐control studies. We also included studies that compared one or more ultrasonography techniques, either independently or in combination, with a reference standard. We excluded case series or case reports (Bossuyt 2008). We excluded studies where X‐ray visualization was not the reference standard or if the tube being placed was a gastrostomy or enteric tube. We defined gastrostomy tubes as tubes for percutaneous enteric access and enteric tubes as both nasal or oral gastrojejunal tubes and small bowel tubes (Boullata 2017). We excluded studies if we could not extract true positive, false negative, false positive, and true negative values.

Participants

Both adults (aged greater than 16 years) and children (aged 16 years or less) who needed gastric tube placement.

Index tests

Ultrasonographic confirmation of gastric tube placement. We included all studies regardless of where the ultrasound test was performed (e.g. bedside or X‐ray department) or who performed and interpreted the test (e.g. ultrasonographer or physician).

Target conditions

The target condition was appropriate gastric tube placement as defined by the primary study authors.

Reference standards

The reference standard was X‐ray of the chest or abdomen (X‐ray visualization). If misinterpretation of the X‐ray was not reported in the included studies, we considered X‐ray of the chest or abdomen to have 100% sensitivity and 100% specificity. We accepted the X‐ray interpretation as defined by the primary study authors.

Search methods for identification of studies

Electronic searches

We systematically searched the following databases in February 2016. We performed an updated search on 15 Apr 2023 for this update.

• the Cochrane Library (Cochrane Central Register of Controlled Trials (CENTRAL) and Cochrane Database of Systematic Reviews (CDSR)) (2021, Issue 6) (Appendix 1)

• MEDLINE (Ovid MEDLINE(R) In‐Process & Other Non‐Indexed Citations and Ovid MEDLINE(R) 1946 to 15 April 2023) (Appendix 2)

• Embase (Ovid) (1974 to 15 April 2023) (Appendix 3)

• National Institute for Health Research (NIHR) PROSPERO Register (up to 17 July 2021) (www.crd.york.ac.uk/prospero/)

• ClinicalTrials.gov (up to 17 July 2021) (clinicaltrials.gov/) (Appendix 4)

• the International Standard Randomised Controlled Trial Number (ISRCTN) registry (up to 17 July 2021) (www.isrctn.com/) (Appendix 5)

• World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (up to 17 July 2021) (www.who.int/ictrp/en/) (Appendix 6)

We used controlled indexing terms and free‐text terms as well as variations of root words. Key terms related to 'ultrasound' were combined using the set operator "AND" with key terms related to 'stomach tube'. We excluded animal studies.

We applied no language restrictions.

Searching other resources

We searched for additional references by cross‐checking bibliographies of retrieved full‐text papers. We searched citations and references using Scopus (www.elsevier.com/solutions/scopus). We contacted common manufacturers of ultrasound devices to seek additional or unpublished studies.

We contacted the top five manufacturing companies according to their global market share in ultrasound devices: GE Healthcare, Philips, Hitachi‐Aloka, Toshiba, and Siemens (IHS Markit 2018).

Data collection and analysis

Selection of studies

We used the methods outlined in the Cochrane Handbook for Systematic Reviews of Diagnostic Test Accuracy (Deeks 2023). Two review authors independently screened titles and abstracts identified by the search strategy. We retrieved the full text of potentially relevant studies and two review authors independently assessed the text against the eligibility criteria outlined in the Criteria for considering studies for this review section. We resolved differences by consensus. We provided details of both included and excluded studies in the Characteristics of included studies and Characteristics of excluded studies tables.

Data extraction and management

The two review authors independently extracted data on study characteristics, participant demographics, sample size, test methods, methodological quality, sensitivity, and specificity. Then, both review authors extracted data to construct a 2 × 2 contingency table including true positive = correct gastric tube placement and correct visualization by ultrasound; false positive = incorrect gastric tube placement but failure to visualize by ultrasound; false negative = correct gastric tube placement but failure to visualize by ultrasound; true negative = incorrect gastric tube placement and correct visualization by ultrasound. If multiple attempts were made to insert the tube, we extracted the number of attempts. We resolved disagreements by consensus and with the help of the other review author. We used Microsoft Excel to manage the data.

Assessment of methodological quality

We used the QUADAS‐2 tool tailored to this review to assess the quality of studies (Whiting 2011). We recorded the assessment in the Characteristics of included studies table. The items assessed are described in detail in Appendix 7 including the additional signalling question included as part of tailoring the tool.

For each item in the quality assessment form, we included a description of how the study addressed the issue and entered a judgement of 'low', 'high', or 'unclear' for an overall risk of bias for each of the four domains. In addition, we added a judgement of 'low', 'high', and 'unclear' for the overall concern of applicability to the review question for domains one, two, and three. We presented an Assessment of methodological quality, which showed all judgements made for all included studies. Two review authors independently assessed methodological quality. We resolved disagreements by discussion between the review authors, with a third review author acting as an arbiter.

Statistical analysis and data synthesis

We planned to analyze data using the methods recommended in the Cochrane Handbook for Systematic Reviews of Diagnostic Test Accuracy (Deeks 2023). We assumed that the data were binary (either appropriate placement or not). Therefore, no threshold or cut‐off value for positivity was required. For each study, we calculated sensitivity and specificity for the detection of appropriate gastric tube placement from 2 × 2 contingency tables.

We presented individual study estimates of sensitivity and specificity graphically in forest plots and in receiver operating characteristics (ROC) space using Review Manager (RevMan 2020). We analyzed data descriptively and presented findings on plots and in tables.

Due to sparse data for estimation of specificity, we performed a meta‐analysis of only sensitivity using a univariate random‐effects logistic regression model to combine data from studies that used the same method and echo window. We presented the median or range (or both) of the specificity reported in the included studies when appropriate.

All analyses were undertaken using Review Manager (RevMan 2020), or STATA software, version 13.0 (Stata).

Investigations of heterogeneity

Due to the limited data, we could not perform the planned meta‐regression analysis. Instead, we added the analysis to plot the sensitivity and specificity as per the subgroup of echo methods and echo window, and a meta‐analysis for sensitivity by a univariate random‐effects logistic regression model.

Sensitivity analyses

Due to the limited data, we could not perform the planned sensitivity analysis. Instead, we separately described the diagnostic accuracy of ultrasound for confirmation of gastric tube placement for children (aged 16 years or less), or for drainage in settings where X‐ray facilities were not readily available for the clinical implications.

Assessment of the certainty of evidence

We used Cochrane methods to develop a table summarizing our findings, employing GRADEpro GDT for evaluation (Deeks 2023; GRADEpro GDT). We estimated the absolute numbers of true positives and false negatives using the prevalence estimates. The prevalence estimates were derived from previous studies that reported on the proportion of misplacement incidents in blind tube insertions (Sparks 2011; Taylor 2021). Two review authors (YT and YK) independently conducted the assessment, which involved study limitations (risk of bias), consistency of effect, imprecision, indirectness, and publication bias (Schünemann 2020). Two review authors (YT and YK) independently judged the certainty of evidence, and resolved disagreements by discussion.

The detailed assessment of each domain according to the GRADE approach was as follows.

• Risk of bias: using the QUADAS‐2 tool.

• Indirectness: evaluated with respect to the population, which included the disease spectrum, setting, interventions, and outcomes, specifically the measures of accuracy. The prevalence of the target condition in the studies was also considered as an indicator of potential indirectness within the population.

• Inconsistency: according to GRADE guidelines, there is a recommendation to downgrade the certainty of evidence for unexplained inconsistency in sensitivity and specificity estimates. As we were unable to perform the prespecified subgroup analyses, we further explored inconsistency by examining the individual point estimates in the forest plots and assessing whether they were broadly similar. We also looked at the confidence intervals (CI) to check for overlap.

• Imprecision: the assessment of imprecision was based on the width of the 95% CI for the summary estimates. We focused on critical outcomes: false negatives and false positives, guiding our imprecision judgements. Imprecision also related to sample size, affecting sensitivity and specificity. The inherent uncertainty of point estimates and the associated participant numbers were taken into account. We recognize that the determination of imprecision is inherently subjective.

• Publication bias: we assessed the comprehensiveness of the literature search, and sought unpublished studies through trial registry searches and by reaching out to field experts and industry. We did not explore reporting bias due to a lack of suitable statistical methods (Deeks 2013).

Results

Results of the search

Search results for the previous version of this review

The initial search identified 953 references through the electronic searches of CENTRAL (26 records), MEDLINE (330), and Embase (597). One record was identified through other sources (citation search of relevant guidelines). No additional reports were identified through NIHR Prospero Register, ClinicalTrials.gov, ISRCTN registry, or WHO ICTRP.

After removing 147 duplicates, we excluded 791 records by reading the titles and abstracts. Of the remaining 19 references, we excluded nine based on the full texts. This resulted in the inclusion of 10 references of 10 studies. We identified no additional reports through citation search of included studies or enquiry of manufacturing companies.

Search results for the current version of this review

Our updated search strategy yielded 1708 records after removal of duplicates. Of these, we excluded 1668 records after titles and abstracts screening. We excluded 21 based on full‐text screening, and five were ongoing or unpublished studies. As a result, there are 12 new studies (14 papers), totalling 22 studies in this update (Figure 2).

2.

Methodological quality of included studies

The methodological quality of the included studies is shown in the Characteristics of included studies table, and Figure 3.

3.

Risk of bias and applicability concerns summary: review authors' judgements about each domain for each included study.

No study was assigned low risk of bias or low concern for applicability in every QUADAS‐2 domain assessed. Six studies presented high risk of participant selection bias because they performed the index test after they confirmed the correct position by whoosh test (a rapid injection of air into the gastric tube while auscultating in the epigastric region), excluded patients who failed to place gastric tube, or excluded patients with inconclusive ultrasound diagnosis (Brun 2014; Chenaitia 2012; Claiborne 2020; Dias 2019; Mumoli 2021; Wong 2017), 12 had unclear risk (Abily 2019; Atalay 2016; Basile 2015; Brun 2012; Gok 2015; Kim 2012; Lock 2003; McMullen 2021; Nedel 2017; Nikandros 2006; Radulescu 2015; Tai 2016), and four had low risk (Güllüpınar 2022; Vigneau 2005; Yildirim 2018; Zatelli 2017).

One study presented high risk of bias in the interpretation of results derived from the index test because a single examiner interpreted the index test and the reference standard (Radulescu 2015), five had unclear risk (Abily 2019; Basile 2015; Nedel 2017; Nikandros 2006; Tai 2016), and 16 had low risk (Atalay 2016; Brun 2012; Brun 2014; Chenaitia 2012; Claiborne 2020; Dias 2019; Gok 2015; Güllüpınar 2022; Kim 2012; Lock 2003; McMullen 2021; Mumoli 2021; Vigneau 2005; Wong 2017; Yildirim 2018; Zatelli 2017).

We rated seven studies with high applicability concerns as the echo models were outdated, such as using cathode‐ray tube displays. These machines are expected to be inaccurate compared with recent machines (Brun 2012; Brun 2014; Gok 2015; Kim 2012; Lock 2003; Nikandros 2006; Vigneau 2005).

We considered one study to have high risk of bias in the reference standard domain because this study did not prespecify criteria for the reference standard and the same person interpreted both X‐ray and ultrasound results (Radulescu 2015). In the reference standard domain, we judged 12 studies at unclear risk of bias mostly because it was unclear if the reference standard results were interpreted without knowledge of the results of the index tests (Abily 2019; Basile 2015; Brun 2012; Brun 2014; Chenaitia 2012; Claiborne 2020; Gok 2015; Lock 2003; McMullen 2021; Nikandros 2006; Yildirim 2018; Zatelli 2017), and nine at low risk (Atalay 2016; Dias 2019; Güllüpınar 2022; Kim 2012; Mumoli 2021; Nedel 2017; Tai 2016; Vigneau 2005; Wong 2017).

Two studies presented high risk of bias in the 'flow and timing' domain because of the number of inconclusive ultrasonography results (Mumoli 2021), or because they reported the possibility of a long time gap (greater than four hours) between the index test and the reference standard (Lock 2003); 17 had unclear risk (Abily 2019; Atalay 2016; Basile 2015; Brun 2014; Claiborne 2020; Dias 2019; Gok 2015; Güllüpınar 2022; Kim 2012; McMullen 2021; Nedel 2017; Nikandros 2006; Radulescu 2015; Tai 2016; Wong 2017; Yildirim 2018; Zatelli 2017), and three demonstrated low risk (Brun 2012; Chenaitia 2012; Vigneau 2005). In the 'flow and timing' domain, the time gap presents a risk of bias because a person may feel uncomfortable when a tube remains in a misplaced position for a long time.

Findings

Participants

Overall, we included 1939 participants and 1944 tube insertions for this review. The number of appropriate tube placements was 1710 insertions (92%) and the number of misplacements was 152 insertions (8%). The mean age of participants in the studies ranged from 11 days to 85 years, many were 50 to 60 years old (some studies did not report the range) (Table 5). Three studies assessed the diagnostic accuracy of ultrasound for gastric tube placement confirmation in children (aged 16 years or less) (Atalay 2016; Claiborne 2020; Dias 2019).

1. Characteristics of included studies.

Study ID	Male:female	Age (mean ± SD)	BMI (mean ± SD) (kg/m2)	Children	Non‐sedated	Sedated	Intubated	Diameter of tube (Fr)	Setting
Abily 2019	NR	NR	NR	NR	NR	NR	NR	NR	ICU
Atalay 2016	13:8	50.95 ± 60.49 months	nr	21	0	19	19	NR	ICU
Basile 2015	NR	NR	NR	NR	NR	NR	NR	NR	NR
Brun 2012a	56:24	52 ± 23 years	NR	0	0	96	96	14 or 16	Prehospital
Brun 2014a	18:14	57 ± 17 years	NR	0	22	32	32	14 or 16	Prehospital
Chenaitia 2012a	77:53	55.7 ± 19.8 years	NR	0	0	130	130	14–18	Prehospital
Claiborne 2020	14:12	2.6 ± 3.9 years	NR	26	NR	NR	NR	5 to 16	EMS
Dias 2019	89:70	10.94 ± 16.82 days	NR	159	NR	NR	NR	6.5	ICU
Gok 2015	32:24	48.4 ± 28.9 years	27.1 ± 6.4	0	0	56	56	10 to 14	ICU
Güllüpınar 2022	52:32	69.77 ± 14.31 years	27.69 ± 3.55	0	NR	NR	54	16	ICU
Kim 2012	28:19	57.6 ± 17.2 years	NR	0	0	27	27	16	EMS
Lock 2003	NR	59.2 ± 16.2 years	NR	NR	NR	50	50	14 or 16	ICU
McMullen 2021	15:10	61.8 ± 13.8 years	28.1 ± 6.4	0	NR	25	25	12 to 14	ICU
Mumoli 2021	307:179	77.4 ± 11.9 years	27.5 ± 5.1	0	NR	NR	NR	10 to 16	Medical wards
Nedel 2017	22:19	Median 62 (IQR 48.5–68) years	Median 22 (IQR 19.2–28)	NR	NR	41	41	NR	ICU
Nikandros 2006	9:7	66.3 ± 7.1 years	NR	NR	0	16	16	NR	ICU
Radulescu 2015	NR	NR	NR	NR	NR	NR	NR	NR	NR
Tai 2016	27:45	84.76 ± 8.46 years	NR	0	NR	NR	NR	NR	EMS
Vigneau 2005	18:16	62.2 ± 19.8 years	24.8 ± 5.8	0	14	26	26	12	ICU
Wong 2017	59:41	NR	NR	NR	100	0	0	14–16	EMS
Yildirim 2018	27:22	58.3 ± 22.7 years	NR	0	49	0	0	16	EMS
Zatelli 2017	80:34	Mean 52 (range 14–89) years	NR	0	NR	100	100	NR	ICU

BMI: body mass index; EMS: emergency medical service; ICU: intensive care unit; IQR: interquartile range; NR: not reported; SD: standard deviation.
^a Reports from the same research group.

Participants of seven studies were all intubated (Brun 2012; Brun 2014; Chenaitia 2012; Gok 2015; McMullen 2021; Nedel 2017; Nikandros 2006). Over half of the participants of five studies were intubated (90% of Atalay 2016; 57% of Kim 2012; 64% of Güllüpınar 2022; 79% of Vigneau 2005; 88% of Zatelli 2017). One study of 55 participants reported that 50 (83%) of 60 tube insertions were performed in intubated participants (Lock 2003). The number of intubated participants in seven studies was unclear (Abily 2019; Basile 2015; Claiborne 2020; Dias 2019; Mumoli 2021; Radulescu 2015; Tai 2016). One study included 14 (42%) non‐sedated participants (Vigneau 2005). One study of 55 participants reported that nine (15%) of 60 tube insertions were performed in non‐sedated participants (Lock 2003). Participants of seven studies were either sedated or intubated (Brun 2012; Brun 2014; Chenaitia 2012; Gok 2015; Kim 2012; Lock 2003; Nikandros 2006). The number of non‐sedated participants in eight studies was unclear (Abily 2019; Basile 2015; Claiborne 2020; Dias 2019; Güllüpınar 2022; Mumoli 2021; Radulescu 2015; Tai 2016). Studies that provided demographic details of participants reported approximately equal numbers of males and females. Eleven studies were in an intensive care unit (ICU) setting (Abily 2019; Atalay 2016; Dias 2019; Gok 2015; Güllüpınar 2022; Lock 2003; McMullen 2021; Nedel 2017; Nikandros 2006; Vigneau 2005; Zatelli 2017). Three studies were in prehospital settings (Brun 2012; Brun 2014; Chenaitia 2012). Five studies were in the emergency medical service (Claiborne 2020; Kim 2012; Tai 2016; Wong 2017; Yildirim 2018). It was considered that ultrasound was performed at the bedside in eight studies (Brun 2012; Brun 2014; Chenaitia 2012; Gok 2015; Kim 2012; Lock 2003; Nikandros 2006; Vigneau 2005). Two studies had an unknown setting (Basile 2015; Radulescu 2015). Six studies reported mean or median participant body mass index ranging from 22 kg/m² to 28 kg/m² (Gok 2015; Güllüpınar 2022; McMullen 2021; Mumoli 2021; Nedel 2017; Vigneau 2005). The diameter of inserted tubes ranged from 6 French to 18 French.

Index test and the reference standard

Ultrasound confirmation methods used

We found several methods when confirming gastric tubes using ultrasound (see Table 1; Table 2; Table 3; Table 4 and Characteristics of included studies table). Nine studies reported the diagnostic accuracy of ultrasound alone (Abily 2019; Brun 2012; Chenaitia 2012; Claiborne 2020; Dias 2019; Gok 2015; McMullen 2021; Nedel 2017; Radulescu 2015), while the others reported the diagnostic accuracy of ultrasound combined with another confirmation method (Atalay 2016; Basile 2015; Brun 2014; Güllüpınar 2022; Kim 2012; Lock 2003; Mumoli 2021; Nikandros 2006; Tai 2016; Vigneau 2005; Wong 2017; Yildirim 2018; Zatelli 2017). Two studies used both air and saline injection (Atalay 2016; Kim 2012). Two studies used dextrose and air injection (Nikandros 2006), or liquid and air injection (Yildirim 2018).

Echo window used

Two studies reported the diagnostic accuracy of ultrasound during tube insertion (ultrasound‐guide insertion) (Gok 2015; Zatelli 2017). We found three visualization methods (echo window) of ultrasound: neck approach (Gok 2015), epigastric approach (Abily 2019; Brun 2012; Chenaitia 2012; Claiborne 2020; Dias 2019; Kim 2012; Lock 2003; Mumoli 2021; Nedel 2017; Vigneau 2005; Wong 2017), and a combination of both (Atalay 2016; Brun 2014; Güllüpınar 2022; McMullen 2021; Radulescu 2015; Tai 2016; Yildirim 2018; Zatelli 2017). Six studies used air injection during ultrasound (Basile 2015; Brun 2014; Güllüpınar 2022; Mumoli 2021; Tai 2016; Wong 2017). Two studies used saline injection (Vigneau 2005; Zatelli 2017). Two studies did not report the echo window (Basile 2015; Nikandros 2006). None of the studies reported any complications related to ultrasound tests.

Performers of index test

The performers' profession of ultrasound varied by study, including: trained nurses (Basile 2015; Güllüpınar 2022; Tai 2016), either physicians or clinical nurses (Mumoli 2021), emergency medicine specialists (Kim 2012), experienced examiners/practitioners (Lock 2003), emergency physicians (Brun 2014; Chenaitia 2012; Wong 2017; Yildirim 2018), paediatric emergency medicine physicians (Claiborne 2020), intensive care physicians (Nedel 2017; Vigneau 2005; Zatelli 2017), radiologists (Atalay 2016), neonatologists (Dias 2019), staff experienced in ultrasonography (Gok 2015), medical officers received ultrasound practice training (McMullen 2021), prehospital services doctors trained in extended Focused Assessment with Sonography for Trauma (eFAST) examination (Brun 2012), and unclear (Abily 2019; Nikandros 2006; Radulescu 2015). Ten studies used special training for ultrasound confirmation of gastric tube, which took one hour to four weeks (Chenaitia 2012; Claiborne 2020; Dias 2019; Güllüpınar 2022; McMullen 2021; Mumoli 2021; Tai 2016; Vigneau 2005; Wong 2017; Zatelli 2017).

Reference standard

It was considered that the performers interpreted the results. All included studies used X‐rays as a reference standard. No misinterpretation of X‐rays among gastric tube position (revealed by other reliable clinical tests) was reported.

Diagnostic accuracy

Seven studies had zero misplacements (Atalay 2016; Claiborne 2020; Dias 2019; McMullen 2021; Nikandros 2006; Vigneau 2005; Zatelli 2017), 14 studies each had fewer than 20 misplacements (Abily 2019; Basile 2015; Brun 2012; Brun 2014; Chenaitia 2012; Gok 2015; Güllüpınar 2022; Kim 2012; Lock 2003; Nedel 2017; Radulescu 2015; Tai 2016; Wong 2017; Yildirim 2018), and the remaining study had 77 misplacements (Mumoli 2021). Four studies had lower sensitivity or specificity estimates than those of the other studies (Abily 2019; Basile 2015; Kim 2012; Lock 2003).

The summary sensitivity of ultrasonography on neck and abdomen echo windows were 0.96 (95% CI 0.92 to 0.98; 3 studies, 179 participants; moderate‐certainty evidence) for air injection (Table 1), and 0.98 (95% CI 0.83 to 1.00; 4 studies, 226 participants; moderate‐certainty evidence) for saline injection (Table 2). The summary sensitivity of ultrasonography on abdomen echo window was 0.96 (95% CI 0.65 to 1.00; 3 studies, 557 participants; very low‐certainty evidence) for air injection (Table 3) and 0.97 (95% CI 0.95 to 0.99; 4 studies, 340 participants; moderate‐certainty evidence) without any injection (Table 4).

Discussion

Summary of main results

This updated review assessed the diagnostic accuracy of ultrasound for gastric tube placement confirmation. Most results showed high point estimates for correct tube detection (sensitivity) (Figure 4). We found considerable clinical heterogeneity among the included studies in terms of echo window, combination of ultrasound with other methods (e.g. saline flush visualization by ultrasound) and ultrasound during insertion of the tube. Despite the inclusion of 12 new studies since the previous version of this review, we could not meta‐analyse specificity due to sparse data with several studies having no misplacements and so specificity was not estimable in these studies. Thus, our meta‐analyses focused on sensitivity for reasonably homogeneous groups of studies.

4.

Forest plot of diagnostic accuracy of ultrasound. The studies were sorted by area of visualisation and ultrasound method.

Among studies that evaluated the diagnostic accuracy of ultrasound on its own, we found three different visualization methods reported: neck approach (Gok 2015), epigastric approach (Abily 2019; Brun 2012; Chenaitia 2012; Claiborne 2020; Dias 2019; Kim 2012; Lock 2003; Mumoli 2021; Nedel 2017; Vigneau 2005; Wong 2017), and a combination of both neck and epigastric approaches (Atalay 2016; Brun 2014; Güllüpınar 2022; McMullen 2021; Radulescu 2015; Tai 2016; Yildirim 2018; Zatelli 2017).

We hypothesized that ultrasound could be an alternative to X‐ray. However, given the reported specificity with wide CIs and the serious complications of misinterpreting a wrong placement as a correct placement, it may be difficult to determine the position of the gastric tube by ultrasonography alone (Figure 4). In addition, there were limited data on the accuracy of tube placement in children or in a prehospital setting.

Strengths and weaknesses of the review

Strengths and weaknesses of included studies

We contacted the authors of included studies and some authors provided us with unpublished details of studies for the review. The authors who provided additional information are presented in the Acknowledgements section. The weakness of our review is the inclusion of three studies from the same research group (see Table 5) (Brun 2012; Brun 2014; Chenaitia 2012). In addition, we calculated diagnostic accuracy based on the number of tube insertions, rather than the number of participants, using 60 tube insertions among 55 participants.

Strengths and weaknesses due to the search and selection process

A strength of this review is that we placed no restrictions on the language of publication and we conducted a comprehensive search using both controlled terms and free words (de Vet 2008). We avoided using search filters because of their limited sensitivity (Beynon 2013). We undertook additional searches to find related articles by contacting major companies of ultrasound devices to obtain unpublished data. We also performed a citation search of included studies, major guidelines (ENA 2019; ESPN guidelines 2020; JSPEN Guideline 2013; SCCM and ASPEN Guidelines 2016), and previous related reviews (Irving 2014; Milsom 2015; Lin 2017), regarding gastric tube placement or parenteral feeding. Therefore, we minimized the risk of missing relevant studies. Little is known about the mechanisms of publication bias for diagnostic accuracy studies and so it is not possible to estimate the impact of unpublished studies on our findings. Nevertheless, the studies included in this systematic review are likely to be the majority of studies that provided evidence on this topic.

We did not employ Web of Science for our citation search strategy (apps.webofknowledge.com/), and acknowledge that we may have missed some studies despite the otherwise comprehensive search.

Assessment of methodological quality and quality of reporting

Our review had several weaknesses in terms of the methodological quality of the included studies (Figure 3). Six studies had high risk of participant selection bias because they performed the index test after they confirmed the correct position by whoosh test or auscultation (Brun 2014; Chenaitia 2012; Claiborne 2020; Dias 2019), exclusion of patients who failed to be placed a gastric tube (Wong 2017), or exclusion of patients with inconclusive results (Mumoli 2021). We should note that only one study had some participants with inconclusive ultrasound diagnoses (Mumoli 2021), while others did not report such findings clearly. Especially in diagnostic tests without numerical cut‐offs, such as ultrasound, it is necessary to report in detail the uncertain diagnostic findings encountered in clinical practice. One study had high risk of bias in the interpretation of results derived from the index test because a single examiner interpreted the index test and the reference standard (Radulescu 2015). We considered that one study had a high risk of bias in the reference standard because the use of prespecified criteria was unclear and the same person interpreted all the results of X‐ray and ultrasound (Radulescu 2015). In the participant selection and reference standard domains, risk of bias was unclear for most studies owing to poor reporting. We encourage authors of future studies to follow the recommendations in the STARD (Standards for Reporting Diagnostic Accuracy) statement to improve the quality of reporting (Bossuyt 2015).

Weaknesses due to the review analyses

We could not synthesize the estimates of diagnostic accuracy (e.g. summary sensitivity, summary receiver operating characteristics curve) because of the heterogeneity of the included studies. This might make our findings relatively difficult to apply to clinical practice.

Within‐ and between‐study comparisons

One study had an extremely poor diagnostic performance with a sensitivity of 0.50 (95% CI 0.32 to 0.68) and specificity of 0.17 (95% CI 0.02 to 0.48) compared to those of the other studies (Basile 2015). Despite the operators being trained in ultrasound use, their accuracy in determining tube position was poor. The reason was unclear; we requested further details from the authors, but we could not obtain sufficient information for this study.

Comparison with previous research

Milsom and colleagues systematically reviewed the methods to confirm the tube location regardless of gastric or enteric tubes and identified one study of gastric tubes. Their electronic search strategies restricted publications to the English language and they did not use controlled terms (Milsom 2015). In addition, they used a date filter for diagnostic accuracy studies restricting the search to 1985 to 2012.

Although limited, we were able to identify additional studies in children by broadening our search methods compared to the review by Irving and colleagues, who systematically reviewed ultrasound confirmation of gastric tube placement among children but found no studies of interest (Irving 2014). Contrary to the present review, Lin 2017 performed a meta‐analysis of five studies focused on adults and concluded that ultrasonography may be considered clinically useful to confirm correct gastric tube placement.

Applicability of findings to the review question

Population and setting

Most included participants were unconscious, which may reduce the sensitivity to the tube being misplaced in the trachea. Misplaced tubes usually cause discomfort and conscious people may complain about it. Most included studies were in a prehospital setting (unconscious due to severe trauma), ICU setting (mechanically ventilated), or emergency medical service setting. This is consistent with the population we expected to find; however, diagnostic accuracy may change according to the clinical setting, for example, clinicians may be able to perform the test more carefully in convalescent wards.

We considered that the mixture of gastric and transpyloric tube insertions had high concern regarding applicability to the review question in the patient selection domain (Vigneau 2005). In addition, among included studies of 1944 tube confirmations, misinterpretation of X‐ray was not reported. In reality, misinterpretation of X‐rays occurs especially when non‐radiologists read the X‐rays (ECRI and ISMP 2006; Lamont 2011).

Index test

We found various ultrasound methods regarding this review question. Echo windows, use and amount of saline or air, and whether to use Doppler ultrasound or real‐time guidance varied by study. Our subgroup analysis could not determine which echo window had the best diagnostic accuracy due to the small sample size. In addition, some studies did not report their methodology (Basile 2015; Nikandros 2006). Such heterogeneity of the index test might be a concern for the applicability of the findings to clinical practice. We considered that the diagnostic accuracy of real‐time ultrasound during gastric tube insertion had high concern regarding applicability to the review question (Gok 2015; Zatelli 2017). Although this review is current, the resolution and other performances of ultrasound equipment are constantly evolving, and the diagnostic accuracy reported in older studies may not be applicable. In fact, several studies used ultrasonography machines with cathode‐ray tube displays (Brun 2012; Brun 2014; Gok 2015; Kim 2012; Lock 2003; Nikandros 2006; Vigneau 2005).

Reference standard

Most included studies used chest or abdominal X‐rays. Some reported just 'X‐rays'. No study reported misinterpretation or unclear results of X‐rays; however, in clinical settings, misinterpretation of X‐rays is possible. Taking into account the misinterpretations, the misplacement of tubes (especially in unconscious participants) might not be detected by X‐ray. These differences in reference standards may affect the diagnostic accuracy of ultrasound in this review.

Authors' conclusions

Implications for practice.

How is the test positioned in the clinical pathway?

For possible implication for practice, the gastric tube is first inserted into the patient via the nose or mouth, down the oesophagus, and into the stomach. Next, tube placement is confirmed by ultrasound combined with other tests (whoosh test, auscultation, inflation of air, etc.) followed by X‐ray visualization of the tube (e.g. chest X‐ray). If a tube is misplaced and detected by X‐ray visualization, the tubes would be reinserted and a second X‐ray would confirm the position. If ultrasound detects obvious misplacement of the tube with this sensitivity, they would reinsert the tubes and confirm it by X‐ray.

How does the index test perform in relation to its intended role (add, replace, triage)?

Due to sparse data, we did not meta‐analyse specificity or perform analyses to investigate the variability of the observed results. Given the high heterogeneity of the data collected and the low methodological quality, the application of these results to clinical practice is likely to be constrained. Available evidence suggests that ultrasound may play an important role in detecting gastric tube position combined with other confirmation methods (e.g. saline flush visualization by ultrasound). However, when we expect ultrasound to detect placed or misplaced tubes, it is suggested that we could not use it alone as an alternative to X‐rays for the feeding tube. Ultrasound could play an important role as one of the confirmation methods for gastric drainage tubes, especially in settings where X‐ray facilities are not readily available.

Implications for research.

Additional research needed on aspects of tests beyond their accuracy

Available evidence suggests that ultrasound would detect most misplacements and possibly reduce repeated X‐ray scans. Confirmation by X‐ray scans can be difficult for people with tube placement because they have to change their body position to have a hard film plate placed on their back, or stand up for scanning while dealing with uncomfortable tubes hanging from their nose or mouth. X‐ray scans are also linked to a median delay of 2.1 hours from request to report and 4.8 hours in 16% of cases requiring tube repositioning (Taylor 2021). Our review failed to locate studies that reported on the misinterpretation of X‐ray results, despite misinterpretation being reported as the primary cause of undetected feeding misplacement (NHS Improvement 2016). Further research is needed to investigate whether ultrasonography would reduce repeated X‐ray confirmations, patient's discomfort from the procedure, and severe complications of tube feeding (e.g. feeding via a tube misplaced in the trachea resulting in severe pneumonia, pneumothorax, empyema, or pulmonary haemorrhage). In addition, investigation into cost to health care is needed to determine if ultrasound could reduce expenditure on repeated X‐rays. We consider research comparing X‐ray and ultrasound for diagnostic accuracy, patient outcome, and cost is needed.

Further studies of test accuracy that need to be undertaken

Considering the role of ultrasound as a replacement for the widely used X‐ray confirmation, which exposes patients to radiation, the current rate of misplacements is notably low. This results in a very low‐certainty evidence concerning specificity. Even with rare misplacements, it is not clinically feasible to entirely bypass X‐ray imaging. Hence, we believe a more precise evaluation is essential to confidently position ultrasound as a replacement for X‐ray confirmation. To reduce heterogeneity, it may be necessary to standardize diagnostic procedures of ultrasonography for confirmation of gastric tube replacement. We consider that investigation of the potential factors modifying the diagnostic accuracy of ultrasound is needed if data are obtained and acceptable for integration.

What's new

Date	Event	Description
25 July 2024	New citation required but conclusions have not changed	Search updated April 2023; new studies added.
25 July 2024	New search has been performed	Review updated.

History

Protocol first published: Issue 2, 2016
Review first published: Issue 4, 2017

Appendices

Appendix 1. CENTRAL search strategy

1. MeSH descriptor: (Ultrasonography] explode all trees

2. (ultrason* or ultrasound* or echotomograph* or echo tomograph* or echograph* or sonograph* or ultra sound or acoustic):ti,ab,kw (Word variations have been searched)

3. #1 or #2

4. MeSH descriptor: (Intubation, Gastrointestinal] explode all trees

5. ((stomach or gastric or gastro* or intragastric or nasogastr* or nasojejun* or nasoenter* or feeding or fed or feed or fine bore or Ryles) near/5 (tube* or intubat* or tubal)):ti,ab,kw (Word variations have been searched)

6. (g‐tube* or ng‐tube* or nj‐tube* or gj‐tube*):ti,ab,kw (Word variations have been searched)

7. #4 or #5 o #6

8. #3 and #7

Appendix 2. MEDLINE (via Ovid) search strategy

1. exp Ultrasonography/

2. (ultrason* or ultrasound* or echotomograph* or echo tomograph* or echograph* or sonograph* or ultra sound or acoustic).tw,kf.

3. 1 or 2

4. exp Intubation, Gastrointestinal/

5. ((stomach or gastric or gastro* or intragastric or nasogastr* or nasojejun* or nasoenter* or feeding or fed or feed or fine bore or Ryles) adj5 (tube* or intubat* or tubal)).tw,kf.

6. (g‐tube* or ng‐tube* or nj‐tube* or gj‐tube*).tw,kf.

7. or/4‐6

8. 3 and 7

Appendix 3. Embase (via Ovid) search strategy

1. exp Ultrasound/

2. (ultrason* or ultrasound* or echotomograph* or echo tomograph* or echograph* or sonograph* or ultra sound or acoustic).tw,kf.

3. 1 or 2

4. exp nasogastric tube/

5. ((stomach or gastric or gastro* or intragastric or nasogastr* or nasojejun* or nasoenter* or feeding or fed or feed or fine bore or Ryles) adj5 (tube* or intubat* or tubal)).tw,kf.

6. (g‐tube* or ng‐tube* or nj‐tube* or gj‐tube*).tw,kf.

7. or/4‐6

8. 3 and 7

Appendix 4. ClinicalTrials.gov search strategy

Conditions

tube OR tubes OR intubation OR intubations

Interventions

ultrasonography OR ultrasound OR echotomography OR tomography OR echography OR sonography

Appendix 5. International Traditional Medicine Clinical Trial Registry (ISRCTN) search strategy

Conditions

tube OR tubes OR intubation OR intubations

Interventions

ultrasonography OR ultrasound OR echotomography OR tomography OR echography OR sonography

Appendix 6. World Health Organization International Clinical Trials Registry Platform (WHO ICTRP) search strategy

Conditions

tube OR tubes OR intubation OR intubations

Interventions

ultrasonography OR ultrasound OR echotomography OR tomography OR echography OR sonography

Recruitment status

All

Appendix 7. Study quality assessment details

Domain 1: participant selection

Risk of bias: could the selection of participants have introduced bias?

Signalling question 1: was a consecutive or random sample of participants enrolled?

Signalling question 2: was a case‐control design avoided?

Signalling question 3: did the study avoid reinsertion of the tube when participants coughed too much?

Signalling question 4: did the study avoid reinsertion of the tube when participants did not make a bubbling sound?

Signalling question 5 and 6: did the study avoid inappropriate exclusions?

Coughing or the absence of bubbling sounds indicates misplacement of tubes into the airway. If participants experience these tests and receive reinsertion based on the results, referral bias is suspected. In addition, anatomical variation of the neck structure (e.g. larynx, pharynx) may make insertion of gastric tubes more difficult (Der Kureghian 2011; Holland 2013). This point may also affect the difficulty of visualizing the tubes by ultrasound. We classified as 'yes' those studies that excluded people who had difficulties with nasogastric tube insertion or visualization, 'no' for those studies where people did not experience such difficulties, and 'unclear' where this information was not clear.

Applicability: were there concerns that the included participants and the setting did not match the review question?

The inclusion criteria for this review specified studies in which the participants were considered to require gastric tube insertion (not including transpyloric tube) for any reason. Therefore, we anticipated that all the studies in the review were judged as 'low' concern.

Domain 2: index test

Risk of bias: could the conduct or interpretation of the index test have introduced bias?

Signalling question 1: were the index test results interpreted without knowledge of the results of the reference standard?

We classified the study as 'yes' if ultrasound test results were interpreted without knowledge of the reference standard or if ultrasound test results were interpreted before the X‐ray test, 'no' if the ultrasound tests were interpreted with knowledge of the reference standard results, and 'unclear' if this information was not clear.

Applicability: were there concerns that the index test, its conduct or interpretation differed from the review question?

Confirmation of gastric tube placement by ultrasound was an inclusion criterion for this review. In this update, we rated the applicability as 'unclear' if the details of echo machine were not reported. If the echo machine used a cathode‐ray tube display, the resolution would be considered low, so we rated it as 'high' applicability concern.

Domain 3: reference standard

Risk of bias: could the reference standard, its conduct or its interpretation have introduced bias?

Signalling question 1: is the reference standard likely to correctly classify the target condition?

Signalling question 2: were the reference standard results interpreted without knowledge of the results of the index test?

Signalling question 3: were the criteria of reference standard for target condition prespecified?

We classified the studies as 'yes' if the criteria for appropriate gastric tube placement were checked by X‐ray visualization, 'no' if the criteria for verification of placement were by any other methods, and 'unclear' if this information was not clear. We classified the study as 'yes' if X‐ray visualization results were interpreted without knowledge of the index test, 'no' if the X‐ray visualization was interpreted with knowledge of the index test results, and 'unclear' if this information was not clear. We classified the study as 'yes' if the criteria of reference standard for target condition were prespecified, 'no' if the criteria of reference standard for target condition were not prespecified, and 'unclear' if this information was not clear.

Applicability: were there concerns that the target condition as defined by the reference standard did not match the review question?

The target condition is the appropriate placement of a gastric tube in the stomach via the nose or mouth, which may be improved by using prespecified diagnostic criteria for chest X‐ray interpretation (Lamont 2011). We evaluated those studies that used clear diagnostic criteria for X‐ray visualization interpretation as 'low' concern, those that did not use any criteria or where the interpretation was based on an individual clinician's interpretation as 'high' concern, and 'unclear' concern if this information was not clear.

Domain 4: flow and timing

Risk of bias: could the participant flow have introduced bias?

Signalling question 1: did all participants receive the same reference standard?

Signalling question 2: was there an appropriate interval between the index test and reference standard?

Signalling question 3: were all participants included in the analysis?

We classified the study as 'yes' if all participants had the same reference standard, 'no' if the reference standard was different from chest or abdominal X‐ray, and 'unclear' if this information was not clear. If a gastric tube was correctly inserted and initial gastric tube placement was confirmed, continual assessment is still required because some routine activities (e.g. vomiting, coughing, retching) may cause tube displacement (Simons 2012). Therefore, any delay in testing may influence results. However, we set an arbitrary time delay between tests in line with the AACCN 2009, which recommends tube location to be checked at four‐hourly intervals (Simons 2012). We classified the study as 'yes' if the delay was less than four hours, 'no' if the delay was four hours or more, and 'unclear' if the information was not clear.

Uninterpretable results may be present (e.g. unclear chest X‐ray or ultrasound). Additionally, withdrawals from the study may be present. We classified the study as 'yes' if uninterpretable results were reported and the study had no withdrawals or the withdrawals were unlikely to affect the results, 'no' if uninterpretable results were not reported or there were withdrawals that were likely to affect the results, or both, and 'unclear' if this information was not clear.

Data

Presented below are all the data for all of the tests entered into the review.

Tests. Data tables by test.

Test	No. of studies	No. of participants
1 Ultrasound	22	1944

1. Test.

Ultrasound

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Abily 2019.

Study characteristics
Patient Sampling	No detailed information available
Patient characteristics and setting	Country: France Setting: Medical and Cardiosurgical ICU in Rouen University Hospital Study period: from July 2016 to August 2018 Number of participants: 219 Male: not reported Age: not reported BMI: not reported Number of intubated participants: not reported Prehospital examination: no Inclusion criteria: people with new placement of GT, except people in the postoperative period of visceral surgery Exclusion criteria: people in the postoperative period of visceral surgery
Index tests	Description: "gastric US" [ultrasound] Performers of ultrasound: not reported Echo model: not reported Tube diameter: not reported Number of OGTs: not reported Echo window: abdomen Saline flash: not reported Air flash: not reported Real‐time guiding: not reported
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: chest X‐rays Details of interpretation of X‐ray: not reported Misclassification by X‐ray: not reported
Flow and timing	Interval between the index test and reference standard: 50 minutes (mean) Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: not reported
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Unclear
Could the conduct or interpretation of the index test have introduced bias?		Unclear risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Unclear
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Yes
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Unclear
Could the patient flow have introduced bias?		Unclear risk

Atalay 2016.

Study characteristics
Patient Sampling	No detailed information available
Patient characteristics and setting	Country: Turkey Setting: 200 bed university children's hospital and approved by the Clinical Research Ethical Committee of Ondokuz Mayis University Study period: not reported Number of participants: 21 Male: 13 Age: mean 50.95 (SD 60.49) months BMI: not reported Number of intubated participants: 19 Inclusion criteria: aged 1 month to 18 years, monitored and sedated in the critical care unit, and had received an NGT. Exclusion criteria: with severe mid‐face trauma, recent nasal surgery or fracture, coagulation abnormality, recent alkaline ingestion, oesophageal varices or strictures, tracheotomy, chest deformity, or soft tissue infection that would prohibit ultrasound examination were excluded from the study
Index tests	Description: "Sonography was performed with an Acuson X300 ultrasound machine (Siemens, Erlangen, Germany) with an 8.0‐MHz linear array and 5‐MHz convex transducers. Ultrasound examinations included transverse and longitudinal scans performed from the right or left side of the participant's neck. While the GT was observed as a hyperechogenic ring with posterior acoustic shadowing under transverse scanning, 2 parallel hyperechogenic lines in the esophagus lumen during longitudinal scanning verified the location of the GT in the esophagus. At the esophagogastric junction, the GT was directly visualized with longitudinal and angled scans of the epigastrium. Visualizations of the NGT in separate scans of the gastric fundus and antrum were also attempted. We used a linear probe for the study of the neck and a convex probe for the stomach. If the tip of the GT was not visualized, 5 mL of normal saline mixed with 5 mL of air was injected into the GT. A gastric placement of the GT was confirmed by visualizing a hyperechogenic fog in the stomach." Performers of ultrasound: radiologist Echo model: Acuson X30 Tube diameter: not reported Number of OGT: 0 Echo window: both neck and abdomen Saline flash: yes Air flash: yes Real‐time guiding: no
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: a chest X‐ray that included the upper abdomen Details of interpretation of X‐ray: the critical care physician evaluated the position of the NGT tip as a tracheal or gastric placement. Misclassification by X‐ray: no
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: 0 Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Basile 2015.

Study characteristics
Patient Sampling	No detailed information available
Patient characteristics and setting	Country: Italy Setting: not reported Study period: September 2013 to January 2014 Number of participants: 46 Male: not reported Age: not reported BMI: not reported Number of intubated participants: not reported Prehospital examination: no Inclusion criteria: inpatients requiring an NGT Exclusion criteria: not reported
Index tests	Description: "tested with US [ultrasound] (with and without 60 mL of air injected) by trained nurses" Performers of ultrasound: trained nurses Echo model: not reported Tube diameter: not reported Number of OGTs: 0 Echo window: unclear Saline flash: no Air flash: yes Real‐time guiding: no
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: X‐ray Details of interpretation of X‐ray: not reported Misclassification by X‐ray: no
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: not reported
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	No
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Unclear
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Unclear
Could the conduct or interpretation of the index test have introduced bias?		Unclear risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Unclear
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Unclear
Could the patient flow have introduced bias?		Unclear risk

Brun 2012.

Study characteristics
Patient Sampling	No detailed information available
Patient characteristics and setting	Country: France Setting: prehospital Study period: March 2010 to April 2011 Number of participants: 96 Male: 56 Age: mean 52 years; median 53.5 years; SD 23 years BMI: not reported Number of intubated participants: 96 Prehospital examination: yes Inclusion criteria: people intubated by prehospital services that required an NGT Exclusion criteria: aged < 18 years, taken in charge during interhospital transport, suspected fracture of the bones of the base of the skull, and those who had ingested detergents, hydrocarbons, or foaming products.
Index tests	Description: "Titan ultrasound machine in all ambulances. Physicians on board, who were extended Focused Assessment with Sonography for Trauma (eFAST) trained, received 1‐day training for ultrasound verification of GT placement. The standardized method included a leG subcostal view with the ultrasound probe while GT was inserted by EMS staff. If not initially seen on ultrasound, 50 mL of air injected through GT." Performers of ultrasound: prehospital services doctors trained in eFAST examination Echo model: Titan ultrasound machine Tube diameter: 14 or 16 Fr Number of OGTs: 0 Echo window: abdomen Saline flash: no Air flash: yes Real‐time guiding: no
Target condition and reference standard(s)	Target condition: GT replacement: NGT placement Description of reference standard: X‐ray Details of interpretation of X‐ray: chest X‐ray on arrival at the hospital Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	No
Was a case‐control design avoided?	Unclear
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Yes
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Unclear
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			High
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Yes
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Low risk

Brun 2014.

Study characteristics
Patient Sampling	No detailed information available.
Patient characteristics and setting	Country: France Setting: the mobile emergency and resuscitation service of the Marseille Batallion of Mariner Firefighters Study period: November 2012 to May 2013 Number of participants: 32 Male: 18 Age: mean 57 (SD 19) years BMI: not reported Number of intubated participants: 32 Prehospital examination: yes Inclusion criteria: aged ≥ 18 years receiving prehospital care and requiring GT insertion. Exclusion criteria: aged < 18 years, pregnant women, contraindication at GT insertion, interhospital transfers, and absence of X‐ray control.
Index tests	Description: "In the prehospital setting, the emergency physicians checked GT placement using ultrasonography during the GT insertion by the nurse or just after the epigastric auscultation and aspirate method was realized." Performers of ultrasound: emergency physicians Echo model: a portable ultrasound system (Titan, Sonosite, Bothell, Washington) with a micro convex probe (2–4 MHz) Tube diameter: 14–16 Fr Number of OGTs: 0 Echo window: both neck and abdomen Saline flash: no Air flash: yes Real‐time guiding: yes
Target condition and reference standard(s)	Target condition: GT replacement: GT placement Description of reference standard: in‐hospital X‐ray Details of interpretation of X‐ray: final confirmation of GT placement was done by radiography on arrival at a hospital Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		High risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			High
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Chenaitia 2012.

Study characteristics
Patient Sampling	Consecutive sampling
Patient characteristics and setting	Country: France Setting: prehospital Study period: May 2010 to May 2011 Number of participants: 130 Male: 77 Age: mean 55.7 (SD 19.8) years BMI: not reported Number of intubated participants: 130 Prehospital examination: yes Inclusion criteria: aged ≥ 18 years in prehospital settings and requiring GT insertion Exclusion criteria: aged < 18 years, pregnant, interhospital transfers, and absence of X‐ray control
Index tests	Description: "After insertion and securing of GT, the emergency physician verified the correct placement of GT by ultrasound. Technique standardized; probe placed in the subxiphoid area then oriented towards leG upper abdominal quadrant to visualize stomach, with transverse viewing, antrum imaged in a transversal plane in the epigastric area using leG lobe of the liver as an internal landmark, gastric body imaged by angling transducer towards leG subcostal area. Ultrasound examination was considered positive when GT appeared as a hyperechogenic line in the stomach. Video recorded showing GT tip; 2 radiologists reviewed each video to confirm results." Performers of ultrasound: emergency physician following a 1‐day training course Echo model: Titan, Sonosite, portable ultrasound with a convex probe (5–2 MHz); V‐Scan, General Electric Healthcare, ultraportable ultrasound with a phased array probe (1.7–3.8 MHz) Tube diameter: 14–18 Fr Number of OGTs: 0 Echo window: abdomen Saline flash: no Air flash: no Real‐time guiding: no
Target condition and reference standard(s)	Target condition: GT replacement: NGT placement Description of reference standard: X‐ray Details of interpretation of X‐ray: chest X‐ray on arrival at the hospital Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		High risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Low risk

Claiborne 2020.

Study characteristics
Patient Sampling	No detailed information available.
Patient characteristics and setting	Country: USA Setting: free‐standing tertiary paediatric emergency department in a tertiary care free‐standing children's hospital Study period: December 2018 to March 2019 Number of participants: 26 Male: 14 Age: mean 2.6 (SD 3.9) years BMI: not reported Number of intubated participants: not reported Inclusion criteria: all participants enrolled required an abdominal X‐ray for placement confirmation of an NGT or OGT per hospital policy. Patients were prospectively identified based on the treating provider's ordering of a standard‐of‐care X‐ray for NGT or OGT placement. Exclusion criteria: parental or patient refusal
Index tests	Description: "The curvilinear transducer with a frequency of 5‐1 MHz (C5‐1) was placed over the abdomen while the patient was in the supine position and used the iScan feature to optimize the view. The transducer was set to an initial depth of 9 cm and was adjusted if necessary. The transducer was placed transversely over the xiphisternum and was fanned downward and aimed toward the left upper quadrant to visualize the gastric body through the left lobe of the liver. Then, sagittal and transverse sweeps were performed over the epigastric area. If the GT was not identified, the transducer was placed over the left flank in the sagittal position using the spleen as a window. The study was terminated after 10 minutes if GT was not visualized. If a patient was younger than 2 years and the GT was unable to be identified, then the study physician changed to the phased array transducer with a frequency of 4‐2 MHz and smaller footprint (S4‐2) and the same method of sweeping over the epigastric area in the transverse and sagittal planes was repeated for a maximum time of 5 additional minutes. The study was considered positive when the GT could be visualized in the stomach as 2 parallel hyperechoic lines." Performers of ultrasound: paediatric emergency medicine physicians who received 2 hours of training Echo model: Philips Sparq ultrasound machine (Philips Healthcare, Andover, Massachusetts) Tube diameter: median 6 Fr (range: 5–16 Fr) Number of OGTs: not reported Echo window: abdomen Saline flash: no Air flash: no Real‐time guiding: no
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: abdominal X‐ray Details of interpretation of X‐ray: interpreted by a paediatric radiologist Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 2
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		High risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Dias 2019.

Study characteristics
Patient Sampling	No detailed information available.
Patient characteristics and setting	Country: Brazil Setting: tertiary‐level neonatal ICU of a public teaching hospital Study period: October 2016 to July 2017 Number of participants: 159 Male: 89 Age: mean 10.94 (SD 16.82) days BMI: not reported Number of intubated participants: not reported Prehospital examination: no Inclusion criteria: needing GT for feeding; spontaneously breathing without the use of oxygen; no congenital malformations or syndromes; no surgical procedure in the gastrointestinal system. Exclusion criteria: infants with unplanned tube removal, or who needed repositioning of the tube before the ultrasonography examination
Index tests	Description: "The abdominal ultrasonography was performed using 2 approaches for all infants. In the first, the subject was in a dorsal decubitus position, and the transducer was positioned in the middle of the epigastric region, allowing for visualization of the tube passing through the cardia and entering the gastric area. The second approach was conducted with the transducer in the upper right quadrant toward the duodenum, to verify whether the tube was positioned entering the pylorus. A SonoSite M‐Turbo portable device was used (SonoSite, Inc, Bothell, Washington) equipped with a 4‐ to 8‐MHz transducer for this examination. All tests were analyzed in real time by a single neonatologist, with experience in performing ultrasound in newborns. For the purpose of this study, the neonatologist received training by a physician specialist in ultrasound to verify the positioning of the tube in the stomach." Performers of ultrasound: neonatologist received training from a physician specialist in ultrasound Echo model: SonoSite M‐Turbo portable (SonoSite, Inc, Bothell, Washington) equipped with a 4‐ to 8‐MHz transducer Tube diameter: 6.5 Fr Number of OGTs: 0 Echo window: abdomen Saline flash: no Air flash: no Real‐time guiding: no
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: a chest and abdomen X‐ray Details of interpretation of X‐ray: radiological examinations analyzed by a single radiologist with experience in neonatal radiology, and the placement was considered correct when the tube end was observed inside the gastric bladder, which could be located at the bottom, body, or antrum. The placement was considered incorrect when the tube end was visualized above the gastro‐oesophageal junction, in the cardia, pylorus, or duodenal portion. Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: 2 attempts were required in 12 cases (7.55%), and 3 attempts were required in 5 cases (3.14%). There were no complications related to the GT insertion. Number of participants who were enrolled in the study but excluded from the analysis: 3
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		High risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
Were the criteria of reference standard for target condition prespecified?	Yes
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Gok 2015.

Study characteristics
Patient Sampling	No detailed information available.
Patient characteristics and setting	Country: Turkey Setting: ICU at Necmettin Erbakan University Study period: February to July 2014 Number of participants: 56 Male: 32 Age: mean 48.4 (SD 28.9) years BMI: mean 27.1 (SD 6.4) kg/m2 Number of intubated participants: 56 Prehospital examination: no Inclusion criteria: 56 mechanically ventilated patients monitored in the ICU between February and July 2014 who received ultrasound‐guided NGT placement. Exclusion criteria: history of neck surgery (e.g. tracheotomy), anatomic deformity, nasal fracture, severe coagulopathy
Index tests	Description: "The esophagus extends from the level of the cricoid cartilage at the cervical region (at the level of sixth cervical and second thoracic vertebrae) down to the incisura jugularis. At this level, it is localized 0.5–0.75 cm to the left of the midline. The trachea and esophagus can be viewed ultrasonographically below the level of the cricoid cartilage. The patients were placed in the supine and sniffing position before the procedure. Sonographic examination was performed by the same individual, who is experienced in ultrasonography. After stabilization of the trachea, a high‐frequency linear US [ultrasound] probe (10–18 MHz, Esaote, Florence, Italy) was transversely placed over the suprasternal notch. Images were obtained of the isthmus and the 2 lobes of the thyroid gland. By shifting the probe to the left, the concentric layers of the esophagus under the thyroid lobe left to the trachea were attempted to be viewed (Figure 1a). This view reflects the anatomic structure of the esophagus; the inner muscular layer of the esophagus is arranged in a circular and spiral fashion, while the external muscular layer has a longitudinal structure." Performers of ultrasound: staff experienced in ultrasonography Echo model: not reported Tube diameter: 10–14 Fr Number of OGTs: 0 Echo window: neck Saline flash: no Air flash: no Real‐time guiding: yes
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: abdominal X‐ray Details of interpretation of X‐ray: gastric placement of the NGT tip was confirmed with an abdominal X‐ray Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Yes
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Unclear
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			High
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Güllüpınar 2022.

Study characteristics
Patient Sampling	Consecutive sampling
Patient characteristics and setting	Country: Turkey Setting: second‐level ICU managed by emergency physicians Study period: between August 2021 and October 2021 Number of participants: 84 Male: 52 Age: mean 69.77 (SD 14.31) years BMI: mean 27.69 (SD 3.55) kg/m2 Number of intubated participants: 54 Prehospital examinations: no Inclusion criteria: aged ≥ 18 years with an indication for enteral nutrition. Exclusion criteria: aged < 18 years, pregnant, those having undergone neck surgery/gastric bypass surgery, with any anatomical deformity, with a history of midface injury or skull base fracture (or both), oesophageal stenosis or alkaline injury, severe coagulopathy, having an open wound in the area where ultrasound had to be applied, and those who did not consent were excluded from the study.
Index tests	Description: NGT was placed blindly by nurses responsible for the participant's care. The same type and brand of 16‐Fr NGT (Levin polyurethane, radiopaque) used in all participants. After the NGT was placed, the nurse in charge of the study was informed. Ultrasound probe was placed on the subxiphoid region and then directed towards the left upper abdominal quadrant to visualize the stomach area. To confirm the location of the NGT, 20 mL of air was injected with a 50 mL pine‐tipped syringe, and an image of the dynamic hyperechogenic air shadow in the stomach was seen by ultrasound. Performers of ultrasound: 6 emergency nurses working in Bozyaka Training and Research Hospital's 2nd level ICU, with ≥ 5 years of experience Echo model: Mindray M5 (Mindray Medical Corporation, Shenzhen, China) ultrasound machine equipped with a 5‐MHz curved array probe Tube diameter: 16 Fr Number of OGTs: 0 Echo window: both neck and abdomen Saline flash: no Air flash: yes Real‐time guiding: no
Target condition and reference standard(s)	Target condition: NGT placement Description of reference standard: chest X‐ray Details of interpretation of X‐ray: radiographs were interpreted blindly by 2 emergency medicine specialists with ≥ 10 years of emergency department experience. Misclassification by X‐ray: no
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: 0 Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		Low risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Kim 2012.

Study characteristics
Patient Sampling	No detailed information available.
Patient characteristics and setting	Country: South Korea Setting: local emergency centre visited by 55,000 patients annually Study period: May to September 2011 Number of participants: 47 Male: 28 Age: mean 57.6 (SD 17.2) BMI: not reported Number of intubated participants: not reported Prehospital examination: no Inclusion criteria: people with low consciousness in whom correct placement of the NGT was ultimately verified by chest X‐ray; aged > 18 years; underwent NGT insertions for reasons including drug overdose, suspicion of gastric bleeding, endotracheal intubation, and others. Exclusion criteria: normal levels of consciousness, did not undergo a radiological examination after tube insertion
Index tests	Description: "US [ultrasound] examinations included a transversal scan that was performed prior to tube insertion from either the right or left side of the patient's neck. This scan was performed to verify that the esophagus was located behind the respiratory tract. If attenuated ultrasound waves in the far field and the posterior wall of the esophagus were not observed after tube insertion, the GT was considered to be positioned within the cervical esophagus. In the esophagogastric junction, the GT was directly visualized with longitudinal and angled scans of the epigastrium. Visualization of the GT in separate scans of the fundus and the antrum of stomach was attempted. We used linear probe for the study of the neck and convex probe for stomach. If visualization was not possible, 40 cc of normal saline and 10 cc of air were injected through the NGT and if ultrasonography showed dynamic fogging in the stomach, gastric placement of the tube was verified." Performers of ultrasound: emergency medicine specialists Echo model: GE LOGIQ 400, USA Tube diameter: 16 Fr Number of OGTs: 0 Echo window: both neck and abdomen Saline flash: yes Air flash: yes Real‐time guiding: yes
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: chest X‐ray Details of interpretation of X‐ray: chest X rays were interpreted by an emergency medicine specialist who did not perform the ultrasound examinations Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Unclear
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			High
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Lock 2003.

Study characteristics
Patient Sampling	No detailed information available.
Patient characteristics and setting	Country: Germany Setting: internal ICU of a university hospital Study period: not reported Number of participants: 55 (60 attempts) Male: not reported Age: mean 59.2 (SD 16.2) years BMI: not reported Number of intubated participants: 50 Prehospital examination: no Inclusion criteria: people in internal ICU of a university hospital who required a GT to be inserted. Exclusion criteria: not reported
Index tests	Description: "The position of the probe in the stomach was to be documented by visualization of a 50 ml air jet applied via the probe. Sonography was performed by a total of 10 sonographically experienced investigators. The position of the probe was considered correct if a clear air jet could be visualized in the stomach after air insufflation." Performers of ultrasound: experienced examiners/practitioners Echo model: Picker LS 9200; 3.5 MHz or 5 MHz transducer Tube diameter: 14.6 Charrière Number of OGTs: not reported Echo window: abdomen Saline flash: no Air flash: yes Real‐time guiding: unclear
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: X‐ray (lower thorax/upper abdomen) Details of interpretation of X‐ray: a position of the probe in the oesophagus or the lung was considered a false position. The X‐ray examination (which was not part of the diagnostic standard for checking the position of the GT in the ICU) was usually performed as part of the routine examination the following morning or for other medical reasons. Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: 24 hours Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	No
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			High
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	No
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		High risk

McMullen 2021.

Study characteristics
Patient Sampling	No detailed information available.
Patient characteristics and setting	Country: Australia Setting: 12‐bed, mixed medical and surgical intensive care unit Study period: 2016 to September 2019 Number of participants: 25 Male: 15 Age: mean 61.8 (SD 13.8) years BMI: mean 28.1 (SD 6.4) kg/m2 Number of intubated participants: 25 Prehospital examination: not reported Inclusion criteria: admitted to ICU, required endotracheal intubation, and required an NGT for treatment or monitoring of their admitting illness. Exclusion criteria: declined or withdrew consent, aged < 18 years, underwent recent nasal surgery or laparotomy, had a head injury/base of skull fracture, severe facial fracture, BMI > 35 kg/m2, coagulopathy, a cervical spine collar, history of gastrectomy or surgery of the gastro‐oesophageal junction, underwent abdominal trauma, intestinal perforation, oesophageal varices, strictures, trauma, tumour, or pregnancy.
Index tests	Description: ultrasound examinations included the transverse and longitudinal planes on either side of the neck via the oblique plane above the suprasternal notch. Assessors aimed to visualize 2 parallel hyperechogenic lines in the oesophagus lumen in the longitudinal plane and a singular circular hyperechogenic shape in the transverse plane. Abdominal ultrasound examinations aimed to visualize 2 parallel hyperechogenic lines via sweeps in either the sagittal, angled, or transverse planes. Performers of ultrasound: medical officers received a 4‐week period of ultrasound practice training Echo model: American General Electric Company, GE Healthcare Venue 40 Point of Care ultrasound system (General Electric Company, Sydney, Australia) Tube diameter: 12–14 Fr Number of OGTs: 0 Echo window: both neck and abdomen Saline flash: no Air flash: no Real‐time guiding: no
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: chest X‐ray Details of interpretation of X‐ray: all enteral feeding tube positions were verified via chest X‐ray before commencement of use. Misclassification by X‐ray: not reported
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 3
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Mumoli 2021.

Study characteristics
Patient Sampling	Consecutive sampling
Patient characteristics and setting	Country: Italy Setting: medical wards at 8 centres Study period: March 2014 to February 2017 Number of participants: 486 Male: 307 Age: mean 77.4 (SD 11.9) years BMI: mean 27.5 (SD 5.1) kg/m2 Number of intubated participants: not reported Prehospital examination: no Inclusion criteria: aged ≥ 18 years, accepted written informed consent, NGT placement in a patient hospitalized, during a hospital stay Exclusion criteria: aged < 18 years, refusal of written informed consent, pregnancy, life expectancy < 48 hours, tracheostomy, anatomic evident deformity of nose or airways, caustic substance ingestion, neck surgery (also not recent), any cranial fracture, already enrolled in the study, prior positioned NGT during hospitalization
Index tests	Description: "As the first criterion, the GT was directly identified as a single or double hyperechoic line; it was searched for first in the antrum and then the fundus of the stomach. The antrum is located posteriorly to the left hepatic lobe and anteriorly to the pancreas. In a fasting patient the antrum appears in a transverse section like a finger glove, with hypoechoic walls and homogeneous (air‐liquid) content. In a mid‐sagittal epigastric section, the antrum has an ovoid aspect, often described as a “bull's‐eye” pattern. When the volume increases (gastric secretions, water) the antrum appears round with thin walls. The gastric fundus is located in the left superior abdominal quadrant, under the diaphragm, anteriorly to the left kidney and medially to the spleen. The fundus can be difficult to visualize because of its deep position and the acoustic windows of the ribs. We facilitated the visualization of the fundus by two approaches: a left lateral intercostal transsplenic section or a longitudinal section over the midaxillary line. As the second criterion, in patients in whom direct visualization of the GT was not possible, 40 mL of air was injected through the GT. In these cases, gastric placement of the tube was confirmed if ultrasonography showed dynamic fogging in the stomach." Performers of ultrasound: physicians or clinical nurses, experts in ultrasound with a specific 10‐hour training course Echo model: GE, GE Logiq S8 Ultrasound System; GE, GE Vivid T8 Portable Ultrasound System; Philips, Philips Hd5 Color Doppler Ultrasound; Sonosite, Sonosite M‐Turbo Ultrasound Machine; Esaote, Esaote Falco 100 OB / GYN Ultrasound; Esaote, Esaote MyLab 30 Tube diameter: Freka tube 10 Fr; Levin tube 12–16 Fr Number of OGTs: 0 Echo window: abdomen Saline flash: no Air flash: yes Real‐time guiding: yes
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: chest X‐ray Details of interpretation of X‐ray: according to the study protocol, a chest X‐ray was obtained from all of the included participants (posteroanterior views were obtained when possible, but most were anteroposterior views obtained during examinations performed at the bedside). Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 61
Comparative
Notes	The authors reported that 48/548 participants had inconclusive ultrasonography diagnosis. We used the analysis excluding participants with inconclusive findings in our analysis in the present review. The authors performed a sensitivity analysis and found that assuming inconclusive as positive or negative resulted in lower diagnostic accuracy of ultrasonography.
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	No
Could the selection of patients have introduced bias?		High risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	No
Could the patient flow have introduced bias?		High risk

Nedel 2017.

Study characteristics
Patient Sampling	No detailed information available.
Patient characteristics and setting	Country: Brazil Setting: ICU Study period: not reported Number of participants: 41 Male: 22 Age: median 62 (IQR 48.5–68) years BMI: median 22 (IQR 19.2–28) kg/m2 Number of intubated participants: 41 Prehospital examination: not reported Inclusion criteria: people receiving invasive mechanical ventilation with enteral feeding tube insertion in ICU. Exclusion criteria: not reported
Index tests	Description: "The patient is scanned with a 3‐MHz curvilinear probe, performing abdominal examination with sagittal and transverse sweeps through the middle epigastric area, and if GT was not visualized, the probe was oriented towards the left upper abdominal quadrant to visualize the gastric area, identifying both the digestive tract and the tube with the guidewire inside the digestive tract." Performers of ultrasound: an ICU physician with a minimum of 20 examinations' experience in ultrasound GT position technique. Echo model: M Turbo by Sonosite Fuji Film, Bothell, USA Tube diameter: not reported Number of OGTs: not reported Echo window: abdomen Saline flash: no Air flash: no Real‐time guiding: no
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: abdominal X‐rays Details of interpretation of X‐ray: the ICU team prospectively analysed all abdominal X‐rays retrospectively at the end of the study using a blinded method. Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: median 46 minutes (range 20–163 minutes) Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: not reported
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Unclear
Could the conduct or interpretation of the index test have introduced bias?		Unclear risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Yes
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Unclear
Could the patient flow have introduced bias?		Unclear risk

Nikandros 2006.

Study characteristics
Patient Sampling	No detailed information available.
Patient characteristics and setting	Country: Greece Setting: 5‐bed ICU Study period: May to September 2005 Number of participants: 16 Male: 9 Age: mean 66.3 (SD 7.1) BMI: not reported Number of intubated participants: 16 Prehospital examination: no Inclusion criteria: not reported Exclusion criteria: not reported
Index tests	Description: "Confirmation of the nasogastric tube position was made by sonographically identifying the air bubble that comes out of the Levin after injecting a 10 cm3 mixture of 5% dextrose and air as well as by standard radiography. All GTs were inserted by the same individual." Performers of ultrasound: unclear Echo model: ATL, ultramark9 Tube diameter: not reported Number of OGT: not reported Echo window: abdomen Saline flash: yes (5% dextrose) Air flash: yes Real‐time guiding: yes
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: standard X‐ray Details of interpretation of X‐ray: not reported Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	No
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Unclear
Could the conduct or interpretation of the index test have introduced bias?		Unclear risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			High
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Unclear
Could the patient flow have introduced bias?		Unclear risk

Radulescu 2015.

Study characteristics
Patient Sampling	No detailed information available.
Patient characteristics and setting	Country: USA Setting: Stony Brook University Hospital Study period: not reported Number of participants: 32 Male: not reported Age: not reported BMI: not reported Number of intubated participants: not reported Prehospital examination: not reported Inclusion criteria: not reported Exclusion criteria: not reported
Index tests	Description: "First, the anterlateral neck was scanned in high frequency to visualize the gastric tube's characteristic echogenic surface with posterior anechoic shadow in the esophagus. Then, the right diaphragm location was identified by low frequency imaging. Comparisons of ultrasound findings made to chest X‐ray findings. Data collected by a single internal medicine resident." Performers of ultrasound: unclear Echo model: not reported Tube diameter: not reported Number of OGTs: not reported Echo window: both neck and abdomen Saline flash: no Air flash: no Real‐time guiding: not reported
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: chest X‐ray Details of interpretation of X‐ray: unclear Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Unclear
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Unclear
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	No
Could the conduct or interpretation of the index test have introduced bias?		High risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Unclear
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	No
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		High risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Tai 2016.

Study characteristics
Patient Sampling	Consecutive sampling
Patient characteristics and setting	Country: Hong Kong Setting: emergency departments of 3 local hospitals Study period: not reported Number of participants: 72 Male: 27 Age: mean 84.76 (SD 8.46) years BMI: not reported Number of intubated participants: not reported Prehospital examination: no Inclusion criteria: aged > 18 years and required chest or abdominal X‐ray, attended the accident and emergency department with an NGT already inserted or required NGT reinsertion. Exclusion criteria: unstable haemodynamic status or medical history of aortic aneurysm, nasopharyngeal carcinoma, and basal skull fracture; with tracheostomy, surgical problems of the pharynx, larynx, trachea, oesophagus, and stomach, and pregnancy.
Index tests	Description: "The ultrasound scan consisted of three parts: neck scan, epigastric scan, and air injection test. Linear probe (10 MHz) and convex probe (5 MHz) were used for neck and epigastric scan respectively. Transverse and longitudinal neck scan were performed over the neck region. The GT was considered to be positioned within the cervical esophagus if hyperechoic lines were observed in the oesophageal region. For the epigastric scan, the GT was visualised with the appearance of acoustic shadow through transversal and longitudinal scans of the fundus and the antrum of stomach." Performers of ultrasound: nurses received a 1‐day workshop with lecture and practical sections Echo model: not reported Tube diameter: not reported Number of OGTs: 0 Echo window: both neck and abdomen Saline flash: no Air flash: yes Real‐time guiding: no
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: chest or abdominal X‐ray Details of interpretation of X‐ray: radiological confirmation was regarded as the gold standard for confirming the NGT position. Besides, it was the only comparator of this study. Either chest or abdominal X‐ray was interpreted by a physician who was not involved in the consultation process. Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Unclear
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Unclear
Could the conduct or interpretation of the index test have introduced bias?		Unclear risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Unclear
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Vigneau 2005.

Study characteristics
Patient Sampling	Consecutive sampling
Patient characteristics and setting	Country: France Setting: 14‐bed medical ICU in 780‐bed teaching hospital Study period: 2 months Number of participants: 33 (35 tubes) Male: 18 Age: mean 62.2 (SD 19.8) years BMI: mean 24.8 (SD 5.8) kg/m2 Number of intubated participants: 26 Prehospital examination: no Inclusion criteria: all consecutive patients during a 2‐month period who received a weighted tip NGT (12 Charrière, Cair, France) for enteral feeding between 8:30 am and 8:00 pm. Exclusion criteria: weighted‐tip NGT inserted during other periods, when only 1 physician was on duty.
Index tests	Description: "Ultrasound examination was conducted as follows: first the duodenum was examined in the middle epigastric area; if the duodenum and/or GT tip was not visualized, the probe was oriented towards the left upper abdominal quadrant to visualize the gastric area. If the WNGT tip [weighted‐tip NGT] was still not visible, 5 ml normal saline mixed with 5 ml air was injected into the tube to visualize the hyperechogenic "fog" exiting the tip." Performers of ultrasound: intensive care physicians following a 2‐hour training course Echo model: 180 plus Sonosite, Sonosite, Lyon, France Tube diameter: 12 Charrière Number of OGTs: 0 Echo window: abdomen Saline flash: yes Air flash: yes Real‐time guiding: yes
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: X‐ray Details of interpretation of X‐ray: the blinded design of the study required weighted‐tip NGT tip verification by 2 physicians, 1 to interpret the X‐rays and another to perform the ultrasound examination. Each physician was unaware of the other's findings. Misclassification by X‐ray: unclear
Flow and timing	Interval between the index test and reference standard: 24–180 minutes Number of participants who were difficult to place GT: 0 Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		Low risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			High
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
Were the criteria of reference standard for target condition prespecified?	Yes
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Yes
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Low risk

Wong 2017.

Study characteristics
Patient Sampling	Consecutive sampling
Patient characteristics and setting	Country: Hong Kong Setting: Accident and Emergency Department of Pamela Youde Nethersole Eastern Hospital Study period: April 2013 to June 2016 Number of participants: 100 Male: 59 Age: not reported BMI: not reported Number of intubated participants: 0 Prehospital examination: no Inclusion criteria: aged > 18 years and underwent NGT insertions, either in emergency department or by community nurses before emergency department attendance. Exclusion criteria: failure to replace NGT; fine bore NGT that required endoscopic assistance; NGT inserted for gastric deflation in people who were intubated; and failure to obtain consent.
Index tests	Description: "2D US [ultrasound] was first conducted with the patient in supine position. The probe was placed in the subxiphoid area, and was then oriented towards the left upper abdominal quadrant to visualize the stomach. With transverse viewing, the gastric antrum was imaged in a transversal plane in the epigastric area using the left lobe of the liver as an internal landmark; the gastric body was imaged by angling the transducer towards the left subcostal area. A positive finding was defined as the visualization of two parallel hyper‐echogenic lines within the stomach, which signifies the presence of GT. If the probe failed to detect the GT signal, the maneuver was repeated. If no GT could be detected after two scans, the scan result was defined as negative. Then, color Doppler US was performed by injecting 20 ml of air into the GT with a 50 ml syringe. If GT was in‐situ, a simultaneous color Doppler flow signal should be detected by the probe placed over the epigastrium pointing towards the left shoulder. This signal was defined as a positive result in color flow Doppler US." Performers of ultrasound: senior emergency physicians with ≥ 6 years of experience in performing ultrasound who attended a 1‐hour training session, which included a real‐time demonstration of the standard technique, before an independent scan. Echo model: Biosound Esaote Mylab 30CV. The CA 421 curvilinear probe was used with the following settings: frequency 3.5 MHz, dynamic range 5, colour flow Doppler Gain 58%, and a penetration depth of 15 cm Tube diameter: 14 Fr in 66 participants and 16 Fr in 34 participants Number of OGTs: 0 Echo window: abdomen Saline flash: no Air flash: yes Real‐time guiding: no
Target condition and reference standard(s)	Target condition: GT replacement Description of reference standard: chest X‐rays Details of interpretation of X‐ray: interpreted by another emergency physician who was blinded to the ultrasound findings Misclassification by X‐ray: no
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	No
Could the selection of patients have introduced bias?		High risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Yildirim 2018.

Study characteristics
Patient Sampling	Consecutive sampling
Patient characteristics and setting	Country: Turkey Setting: urban hospital's emergency medicine department with 150,000 patient visits a year Study period: 1 February 2016 to 10 June 2016 Number of participants: 49 Male: 27 Age: mean 58.3 (SD 22.7) years BMI: not reported Number of intubated participants: 0 Prehospital examination: no Inclusion criteria: aged > 18 years; indication of NGT placement between the dates mentioned and admitted to adult emergency department (indications included stomach decompression, reducing risk of vomiting and its incidence, observing and evaluating upper gastrointestinal bleeding risk, prolonged ileus, to give medication or oral contrast to non‐swallowing patients, detection of transdiaphragmatic herniation, stomach lavage); voluntarily accepting participation in the trial Exclusion criteria: midfacial injuries and head‐base fractures; coagulopathy; stomach cuff or gastric by‐pass; oesophageal strictures or alkaline injury; did not wish to participate in the study; had open wound in the area to prevent ultrasonography and may have been at risk of infection
Index tests	Description: "US [ultrasound] evaluation was performed. All patients were evaluated by the same physician who was certified in 'bedside ultrasonographic evaluation in emergency care'. Mindray (M5, Hamburg, Germany) US machine was used. A 7.5 MHz linear probe was used for neck visualization at the level of cricoid membrane. A 3.5 MHz convex probe was used to visualize subxiphoid and gastroesophageal region. If the GT could not be verified at the subxiphoid region, 10 cc air and 40 cc liquid mix was given with a pine‐tipped syringe. Ten, US evaluation was repeated. US performer should look for dynamic fogging in the stomach at the tip of the GT." Performers of ultrasound: a physician who has certified in bedside ultrasonographic evaluation in emergency care Echo model: Mindray (M5, Hamburg, Germany) ultrasound machine Tube diameter: 16 Fr Number of OGTs: 0 Echo window: both neck and abdomen Saline flash: yes Air flash: yes Real‐time guiding: no
Target condition and reference standard(s)	Target condition: NGT placement Description of reference standard: chest X‐ray Details of interpretation of X‐ray: not reported Misclassification by X‐ray: no
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		Low risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Unclear
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

Zatelli 2017.

Study characteristics
Patient Sampling	Consecutive sampling
Patient characteristics and setting	Country: Italy Setting: ICU Study period: 8‐month period Number of participants: 114 Male: 80 Age: mean 52 (range 14–89) years BMI: not reported Number of intubated participants: 100 Prehospital examination: no Inclusion criteria: all patients admitted to ICU received a feeding tube upon admission or during their stay. GTs were routinely positioned in all the patients with an incapacity for spontaneous enteral feeding was expected for ≥ 48 hours. Exclusion criteria: not reported
Index tests	Description: "All the gastric tubes were positioned by the nursing staff by measuring the distance from the tip of the patient's nose to the earlobe and from the earlobe to the xiphoid process. The intensivist performed the sonography in real‐time. The intensivist involved had sonographic experience in the positioning of catheters and the visualization of the trachea during percutaneous dilational tracheostomy, in addition to a specific 40‐hour training course with a radiologist. A real‐time portable ultrasound unit (Philips Sparq) equipped with a convex probe with low frequency (2–5 MHz) and a linear probe with high frequency (5–7.5 MHz) was used for this study. The intensivist performed the exam in real time using four steps: sonography from either the right or left side of the participant's neck to visualize the esophagus, sonography of the epigastrium to confirm passage through the esophagogastric junction, the positioning in the antrum, and the sonography of the fundus. Ultrasound examinations included a transversal scan of the neck, before tube insertion to verify that the esophagus was located behind the respiratory tract. The proximal esophagus is visible in the neck through the trachea and the left lobe of the thyroid. The cervical esophagus appears as an oval structure on transverse scans and as a long tubular structure on longitudinal scans. If attenuated ultrasound waves in the far field and the posterior wall of the esophagus were not observed after tube insertion, the gastric tube was considered to be positioned within the cervical esophagus. In the esophagogastric junction, the gastric tube was directly visualized with longitudinal and angled scans of the epigastrium. Visualization of the gastric tube in separate scans of the fundus and the antrum of the stomach was attempted. If visualization of the antrum was not possible, 50 ccs of normal saline was injected through the gastric tube, and if ultrasonography showed dynamic fogging in the stomach, gastric placement of the tube was verified Visualization of the gastric tube in the neck, but not in the esophagogastric junction, in the antrum or in the fundus, was not sufficient to confirm the positioning of the tube because the tube could also be coiled within the cervical esophagus and not proceed distally. The antrum is a landmark located posterior to the left hepatic lobe and anterior to the pancreas (the antrum is delimited anterior to the pancreas in a transversal epigastric section). In a fasting participant, the antrum appears like a finger glove in a transversal section, with hypoechogenic walls and homogeneous (air–liquid) content. In a medium sagittal epigastric section, the antrum has an ovoid aspect, often described as a "bulls‐eye pattern". When the volume increases (gastric secretions, water), the antrum appears round with thin walls. It's more difficult to visualize the antrum with sonography without previous preparation. The gastric fundus is located in the left superior abdominal quadrant, under the diaphragm, anterior to the left kidney, and posterior to the spleen. The fundus can be difficult to visualize because of its deep position and the acoustic windows of the ribs. We facilitated the visualization of the fundus through two approaches: a left lateral intercostal trans‐splenic section or a longitudinal section over the medium‐axillary line." Note: the absence of gastrointestinal markers at specific lengths is used to determine if there had been a misplacement of the tube into the respiratory tract. Performers of ultrasound: an intensivist who had completed a 40‐hour training course Echo model: Philips Sparq Tube diameter: not reported Number of OGTs: 0 Echo window: both neck and abdomen Saline flash: yes Air flash: no Real‐time guiding: yes
Target condition and reference standard(s)	Target condition: NGT placement Description of reference standard: X‐ray Details of interpretation of X‐ray: not reported Misclassification by X‐ray: no
Flow and timing	Interval between the index test and reference standard: not reported Number of participants who were difficult to place GT: not reported Number of participants who were enrolled in the study but excluded from the analysis: 0
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	Yes
How were participants' coughs managed? Did the study avoid reinsertion of the tube when participants coughed too much?	Unclear
How were auscultation findings (e.g. bubbling sounds) dealt with? Did the study avoid reinsertion of the tube when auscultation was not found?	No
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom the GT was difficult to place?	Yes
Did the study avoid inappropriate exclusions? Did the study avoid excluding participants for whom tubes were difficult to visualize?	Yes
Could the selection of patients have introduced bias?		Low risk
Are there concerns that the included patients and setting do not match the review question?			Low concern
DOMAIN 2: Index test (Ultrasound)
Were the index test results interpreted without knowledge of the results of the reference standard?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Low risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference standard
Is the reference standard likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
Were the criteria of reference standard for target condition prespecified?	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?		Unclear risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			Low concern
DOMAIN 4: Flow and timing
Did all patients receive the same reference standard?	Yes
Was there an appropriate interval between the index test and reference standard? We set an arbitrary 4 hours for this review	Unclear
Were all participants included in the analysis? Consider withdrawals and withdrawals who were likely to impact on study results. Also consider the exclusion of 'difficult' participants	Yes
Could the patient flow have introduced bias?		Unclear risk

BMI: body mass index; EMS: emergency medical service; Fr: French; GT: gastric tube; ICU: intensive care unit; IQR: interquartile range; NGT: nasogastric tube; OGT: orogastric tube; SD: standard deviation.

Characteristics of excluded studies [ordered by study ID]

Study	Reason for exclusion
Acosta Pedemonte 2020	Insufficient information on 2 × 2 table
Atalay 2019	Insufficient information on 2 × 2 table
Barberio 2018	Insufficient information on 2 × 2 table
Blaivas 2012	Editorial
Brotfain 2019	Case series
Carmona 2018	Insufficient information on 2 × 2 table
Choi 2021	Case series
CTRI//09/027678	X‐ray was not performed
Dagli 2015	Nasoenteric tubes inserted into the postpyloric area
De Robertis 2019	Index test was not gastric tube
Edroso 2020	Case series
Ferraboli 2022	Insufficient information on 2 × 2 table
Greenberg 1993	Transpyloric tube
Hernandez‐Socorro 1996	Not a diagnostic test accuracy study. Compared method for placing feeding tubes
JPRN‐UMIN000027806	Target condition was not correct gastric tube placement
Kerforne 2013	Case report
Liu 2015	Nasal‐jejunal tube
Lock 1997	Letter
Nasreen 2017	Target condition was not correct gastric tube placement
NCT03430908	X‐ray was not performed
Pellet 2018	Case series
Piton 2017	Case series
Qian 2020	Case series
Scarpellini 2019	Insufficient information on 2 × 2 table
Tamhne 2006	pH‐specific paper used as a reference standard
Tsolaki 2022	Insufficient information on 2 × 2 table
Wagai 1981	Case series
Xiao 2020	Case series
Yadav 2020	Index test was not gastric tube
Yaseen 2022	Insufficient information on 2 × 2 table

Characteristics of ongoing studies [ordered by study ID]

CTRI//05/019427.

Study name	Randomized control trial to compare ultrasound guided naso/orogastric tube placement as compared to standard naso/orogastric tube placement in neonates
Target condition and reference standard(s)	Naso/orogastric tube placement
Index and comparator tests	Index test: ultrasound‐guided naso/orogastric tube placement Comparator test 1: standard naso/orogastric tube placement Comparator test 2: X‐ray
Starting date	28 June 2019
Contact information	Somashekhar Nimbalkar Department of Pediatrics, Pramukhswami Medical College, Karamsad, Anand, Gujarat, India
Notes

NCT02866123.

Study name	Verification of correct positioning of a gastric tube by ultrasonography (SNG echo)
Target condition and reference standard(s)	Nasogastric tube placement
Index and comparator tests	Index test: ultrasonography Comparator test: pulmonary radiography
Starting date	January 2015
Contact information	Centre Hospitalier Universitaire Dijon, Dijon, France, 21079
Notes

NCT04104295.

Study name	The use of ultrasound in nasogastric tube placement in children admitted to the pediatric ICU
Target condition and reference standard(s)	Nasogastric tube placement
Index and comparator tests	Index test: an ultrasound scan of the abdomen within 2 hours of the routine X‐ray Comparator test: X‐ray results
Starting date	24 March 2020
Contact information	Eitan Neeman Yale University – MEDPED Critical Care
Notes

NCT04795895.

Study name	Ultrasound for confirmation of gastric tube placement in critically ill patients under invasive mechanical ventilation
Target condition and reference standard(s)	Gastric tube placement
Index and comparator tests	Index test: ultrasonography Comparator test: chest radiography
Starting date	1 March 2021
Contact information	Ying‐Chun Chien National Taiwan University Hospital Taipei
Notes

Rigobello 2020.

Study name	Accuracy of the combined method (auscultation and pH measurement) and ultrasonography for confirmation of gastric tube placement: a study protocol for a prospective study
Target condition and reference standard(s)	Gastric tube placement
Index and comparator tests	Index test: the combined method (auscultation and pH measurement) and ultrasonography Comparator test: X‐ray
Starting date	Not available
Contact information	Fernanda Raphael Escobar Gimenes Departamento de Enfermagem Geral e Especializada, Universidade de São Paulo Escola de Enfermagem de Ribeirão Preto, Ribeirao Preto, São Paulo, Brazil
Notes

Differences between protocol and review

Our original plan was to search the Aggressive Research Intelligence Facility Databases (ARIF) as part of our research. However, when we attempted to access the database (on 3 June 2022), it was unavailable. Due to the lack of access, we removed any reference to ARIF from the search strategy section of our review.

We planned to present the sensitivity, specificity, positive and negative likelihood ratios, and diagnostic odds ratio for the detection of appropriate gastric tube placement (Glas 2003); however, we did not calculate likelihood ratios and the diagnostic odds ratio because of sparse data. We did not jointly synthesize sensitivity and specificity using a bivariate model because of sparse specificity data. We performed meta‐analysis of only sensitivity using a univariate random‐effects logistic regression model for studies with the same method and echo window. We tailored the QUADAS‐2 tool before application to all included studies in our published protocol for the review because the agreement had been poor and we considered a further refinement of the tool was needed (e.g. omitted unimportant signalling questions) (Whiting 2011).

If any misinterpretation of the X‐ray was reported, we planned to construct another 2 × 2 contingency table that took the misinterpretation into account. For the table, if the misplacement of the tubes was interpreted as correct placement by X‐ray, we planned to ignore the X‐ray result and treat the outcome as misplacement. If the appropriate placement of the tubes was interpreted as misplacement by X‐ray, we planned to ignore the X‐ray result and treat the outcome as an appropriate placement. In addition, we planned to perform sensitivity analyses for this imputation. However, no study reported any misinterpretation of the X‐ray.

If sufficient studies were available, we planned to investigate the following potential sources of heterogeneity by adding variables to the meta‐regression model and using the command xtmelogit in Stata (Harbord 2009; Takwoingi 2013): effects of obesity (BMI over 30 kg/m² or not), effects of tube diameter (up to 14 Fr or 16 Fr and above) and echo window (the neck, abdomen, or both). However, we could not perform these analyses due to limited data. We changed the analysis to plot the sensitivity and specificity as per the subgroup of the echo window.

We also planned to perform sensitivity analyses stratified by methodological quality as per the QUADAS‐2 tool domain and planned to carry out the following sensitivity analyses to explore the robustness of the results:

• excluding studies of non‐sedated people;

• excluding studies of intubated people;

• excluding studies of orogastric tubes;

• excluding studies including reported X‐ray misinterpretation.

The reason for excluding non‐sedated people was because the gag reflex of non‐sedated people may suggest tracheal insertion of the gastric tube, which may affect the diagnostic accuracy of the ultrasound. For intubated people, the tube may be difficult to visualize in the oesophagus behind the trachea, or the tracheal tube itself may block the gastric tube from entering the trachea. We anticipated that there were no differences between the diagnostic accuracy of the nasogastric and orogastric tubes and confirmed the assumption using sensitivity analysis.

However, due to the limited data, we could not perform these analyses.

Contributions of authors

Previous version of the review

HT drafted the protocol and review with contributions from YK and Emma Barber (from the National Center for Child Health and Development).

HT and YK devised the study selection criteria.

HT, YK, YT, MA, and Yuhong (Cathy) Yuan (Trials Search Co‐ordinator) undertook the search strategy.

HT, YK, and YT developed the study design and research question.

HT, YK, and YN developed the statistical analysis/synthesis of the data plan.

HT and Yuhong (Cathy) Yuan ran the search strategy.

HT, YK, and MA screened the search results.

HT and YK extracted the data and assessed the methodological quality.

All review authors contributed to revising the manuscript, reviewed all drafts, and agreed on the final version.

Current update

YT: reviewed the methods and approved minor changes, performed the updated literature search and selection of the search results, re‐extracted data, and conducted risk of bias assessments. Drafted the first version of the manuscript, edited the review, and gave final approval.

YK: performed the updated literature search and selection of the search results, re‐extracted data, and conducted risk of bias assessments. Drafted the first version of the manuscript, provided critical feedback, and gave final approval.

MB: performed the selection of the search results, re‐extracted data, and conducted risk of bias assessments. Drafted the first version of the manuscript, provided critical feedback, and gave final approval.

KA: performed the selection of the search results, re‐extracted data, and conducted risk of bias assessments. Drafted the first version of the manuscript, provided critical feedback, and gave final approval.

AS: performed the selection of the search results, re‐extracted data, and conducted risk of bias assessments. Drafted the first version of the manuscript, provided critical feedback, and gave final approval.

SJ: performed the selection of the search results, re‐extracted data, and conducted risk of bias assessments. Drafted the first version of the manuscript, provided critical feedback, and gave final approval.

Sources of support

Internal sources

• Kyoto University, Japan

External sources

• No sources of support provided

Declarations of interest

YT: is a board member of Cochrane Japan, and received grants from JSPS Kakenhi Grant Number 22K10423, Pfizer Health Research Foundation, and Kyoto University School of Public Health for work other than this review. YT is a Cochrane Editor but was not involved in the editorial process.

YK: received grants from JSPS Kakenhi Grant Number 22K15664, SRWS‐PSG, and Yasuda Memorial Medical Foundation Grant Program for Cancer Research for work other than this review.

MB: none.

KA: received grants from SRWS‐PSG, Fujiwara Memorial Foundation, Research Institute of Healthcare Data Science for work other than this review, and JSPS Kakenhi Grant Number 24K19108.

AS: none.

SJ: none.

New search for studies and content updated (no change to conclusions)