Abstract
Background and Aims:
Real-time ultrasonography has shown good correlation in evaluating gastric emptying in previous studies. The present study aimed to examine gastric content and volume using ultrasound in neurosurgical patients admitted in the intensive care unit (ICU) and compare it with non-neurosurgical patients and assess correlation between gastric emptying and intracranial pressure.
Methods:
Forty adult patients of either gender admitted in the ICU on mechanical ventilation and receiving enteral nutrition via nasogastric tubes were included in the study and allocated into two groups: Group I (n = 20): Neurosurgical patients; Group II (n = 20): Non-neurosurgical patients with chest pathology. All patients were given 300 ml of water through a ryle’s tube and ultrasound-guided gastric volume was assessed at baseline (before feed, T0) and 15 minutes (T1), 1 hour (T2), 2 hours (T3), and 4 hours (T4) after the feed. Gastric volume and gastric emptying rate (GER) were calculated using appropriate formulas. Ocular ultrasound was performed to record optic nerve sheath diameter (ONSD) in all patients.
Results:
There was no significant difference between the two groups in baseline values of gastric volume as well as at T1 and T2, while there was a significant difference between the two groups at T3 and T4. The mean value of GER in group I was 33.80 ± 13.29%, and that in group II was 58.24 ± 9.80% (P < 0.001). There was significant negative correlation between ONSD and GER (Pearson’s correlation coefficient: -0.6; P value < 0.001).
Conclusion:
Mechanically ventilated patients in the ICU who had neurosurgical pathology exhibited delayed gastric emptying as compared to non-neurosurgical patients.
Keywords: Gastric emptying, intracranial pressure, ultrasonography
INTRODUCTION
Gastroparesis is defined as delayed gastric emptying in the absence of mechanical obstruction.[1,2] The incidence of gastroparesis in traumatic brain injury ranges around 45–50% and is closely related to the severity of trauma and intracranial hypertension.[3] The exact cause of delayed gastric emptying in these patients is unknown. However, altered nerve signalling to the stomach may be a causal factor.[4] Intracranial hypertension leads to a biphasic systemic autonomous stimulation. It results from hyperactivity of the parasympathetic and sympathetic systems at different times. Increased intracranial pressure (ICP) causes a massive increase in sympathetic activity, which leads to changes in gastrointestinal motility and water and electrolyte absorption.[5] Few studies in the literature have documented delayed gastric emptying in patients with head injury and raised ICP.[3,6] Potential applications for estimation of gastric emptying in head injury patients are confirming empty stomach prior to the administration of general anaesthesia and the start of enteral nutrition.
Point-of-care gastric ultrasound is an emerging diagnostic tool that allows qualification and quantification of gastric content.[7] Real-time ultrasonography has shown good correlation in previous studies in evaluating gastric emptying.[8,9]
An extensive review of literature indicates that gastric emptying in neurosurgical patients might not be similar to that in non-neurosurgical patients admitted in the intensive care unit (ICU). Furthermore, the association between raised ICP and gut motility is still not well established. There is paucity of relevant literature, and most of the studies are of small sample size or have used different non-standardised techniques. In the light of the above findings, the present study aimed to examine gastric content and volume using ultrasound in neurosurgical patients admitted in the ICU and compare it with non-neurosurgical patients. The null hypothesis was that there is no difference in gastric emptying rate (GER) in patients with or without head injury.
The primary objective was the comparison of the GER between the two groups using ultrasound. Secondary objectives included non-invasive ICP measurement using ultrasonographic measurement of optic nerve sheath diameter (ONSD) and correlation between gastric emptying and ONSD values.
METHODS
This prospective comparative study was conducted in the department of anaesthesiology and critical care in a tertiary care medical college hospital after approval from the biomedical research ethics committee (BREC/22/TH/Anesth-09) from June 2023 to January 2024. Witnessed written informed consent for participation in the study and use of the patient data for research and educational purposes was obtained from the patient’s attendant. The study was registered with http://www.clinicaltrials.gov. The study was carried out according to the principles of the Declaration of Helsinki, 2013 and Good Clinical Practice guidelines.
Adult patients (18–65 years) of either gender with neurosurgical or chest pathology admitted in the ICU on mechanical ventilation and receiving enteral nutrition via nasogastric tubes were included in the study. Patients with diabetes, deranged liver and kidney, Sequential Organ failure Assessment (SOFA) score ≥2, obesity [body mass index (BMI) >25 kg/m2], orbital fracture or tumour, hyperthyroidism/exophthalmos, abdominal trauma or surgery, cervical spine injury, and neuromuscular disorders and patients on prokinetics, inotropes, and neuromuscular relaxants were excluded from the study.
Patients were assessed thoroughly prior to the procedure, and a detailed clinical history was obtained from the attendant of the patient. The weight of the patients was taken according to the ideal body weight. Placement of ryle’s tube was confirmed through auscultation in the epigastric area, and aspiration of the gastric contents was done. The patients in both the groups were sedated with fentanyl (1.5 µg/kg/h) and midazolam (0.06 mg/kg/h) infusion.
Patients were allocated into two groups, that is, Group I (n = 20), which included neurosurgical patients who have undergone surgery for brain tumour or head injury or cerebral aneurysm and admitted in ICU, and Group II (n = 20), which included non-neurosurgical patients admitted in ICU following chest injury or any other chest pathology.
A trained person who had performed more than 25 gastric ultrasonography procedures independently performed all the measurements. A SonoSite M-Turbo (Seattle, Washington, USA) portable ultrasound machine was used to conduct the study. A curved array low-frequency (2–5 MHz) probe was used in abdominal scan mode settings. The probe was lubricated with water soluble jelly, and the epigastrium was scanned in a sagittal plane sweeping the transducer from the left to right subcostal margins. The gastric antrum was identified just below the left lobe of liver and pancreas where the aorta/superior mesenteric artery acts as an important landmark. The readings were taken in the right lateral position. Cross-sectional area (CSA) was measured using the formula: Aantrum = π/4 × D1 × D2, where D1 = anteroposterior and D2 = craniocaudal diameters of the antrum at antrum resting, from serosa to serosa.[10]
Blood sugar level was estimated using a glucometer prior to giving the feeds. The procedure was performed 6 hours after the last feed. All patients were given 300 ml of water through a ryle’s tube, in no more than 5 min, and gastric volume was assessed at baseline (before feed, T0) and 15 min (T1), 1 h (T2), 2 h (T3), and 4 h (T4) after the feed. The mean of three readings was calculated at each time point.
The gastric volume was calculated using the formula:
Volume (ml) = 27.0 + 14.6 × right-lateral CSA (cm2) – 1.28 × age (years)[11]
GER = [(Aantrum 120 min/Aantrum 15 min)-1] ×100.
Ultrasound-guided ONSD was assessed and recorded at similar time points. A trained person having performed more than 25 ocular ultrasounds performed all measurements using a 7.5 MHz linear array probe of sonosite M-turbo ultrasound machine. Patients were placed in supine position with eyes closed with transparent adhesive dressing ensuring no air bubble is present between the eye and the dressing. A thick layer of sterile coupling was applied to the closed upper lid, and the probe was placed gently on the gel on the superior and the lateral aspect of the upper lid without exerting any pressure on the eyeball. Then the probe was angled slightly caudally and medially until axis view of the orbit was obtained displaying the entry of the optic nerve into the globe. Depth and gain were adjusted accordingly. The image was frozen, and the cursor was placed on the outer contour of the dural sheath at the retrobulbar position, 3 mm behind the globe and perpendicularly to the optic nerve axis. The ONSD was calculated as horizontal distance between the two cursors.
The sample size for the study was based on a study by Kao et al.,[6] who reported the mean gastric emptying time (GET) 1/2 (min) in the two groups as follows: Group 1 (healthy volunteers) = 29.4 ± 3.7; Group 2 (head injury patients) = 57.2 ± 20.8. Assuming 99% power and 95% confidence interval, the minimum calculated sample size for each arm was 12. However, to compensate for dropouts, we enroled 20 patients in each group.
Haemodynamic parameters [heart rate (HR) and mean arterial pressure (MAP)] were monitored throughout and recorded at baseline and at 15 minutes, 1 hour, 2 hours, and 4 hours after the feed.
Data were coded and recorded in Microsoft Excel spreadsheet program. Statistical Package for the Social Sciences v23 (International Business Machines Corp., United States of America) was used for data analysis. Descriptive statistics were elaborated in the form of means/standard deviations and medians/interquartile ranges (IQRs) for continuous variables, and frequencies and percentages for categorical variables. Group comparisons for continuously distributed data were made using independent sample ‘t’ test when comparing two groups. If data were found to be non-normally distributed, appropriate non-parametric tests in the form of Wilcoxon test were used. Chi-squared test was used for group comparisons for categorical data. In case the expected frequency in the contingency tables was found to be 20% of the cells, Fisher’s exact test was used instead. Linear correlation between two continuous variables was explored using Pearson’s correlation (if the data were normally distributed) and Spearman’s correlation (for non-normally distributed data). Statistical significance was kept at P < 0.05.
RESULTS
A total of 40 adult patients completed the study [Figure 1]. Demographic parameters were statistically similar between the two groups [Table 1]. Group I comprised 20 patients, out of which 16 patients had traumatic brain injury, two patients had brain tumour, and two patients had hypertensive bleed. Group II comprised 20 patients, out of which nine patients had chest injury, three patients had acute respiratory distress syndrome (ARDS), and eight patients had chronic obstructive pulmonary disease (COPD). HR and MAP values were comparable between the two groups at all timepoints (P > 0.05). Table 2 shows mean values of gastric volume between the groups. There was no significant difference between the two groups in baseline values of gastric volume, as well as at T1 and T2, while there was a significant difference between the two groups at T3 and T4. The mean value of GER (%) in group I was 33.36 (13.20) and that in group II was 58.13 (9.89) {mean difference (MD) [95% confidence interval (CI)] 24.44 (16.97, 31.91); P < 0.001}. A GER of <45% was present in 16 patients of group I and two patients of group II, with a P value of <0.001 [Table 3]. The difference in ONSD values was statistically significant between the two groups at all timepoints [Table 4]. There was statistically significant negative correlation between ONSD and GER (Pearson’s correlation coefficient: -0.6), with a P value of <0.001 [Figure 2].
Figure 1.
Flow diagram. n: Number of patients
Table 1.
Demographic parameters
| Parameter | Group I Mean (SD) | Group II Mean (SD) | Mean difference (95% Confidence interval) | P |
|---|---|---|---|---|
| Age (years) | 32.25 (11.28) | 36.75 (8.06) | 4.50 (-1.78, 10.78) | 0.156 |
| Gender (Male/Female) | 19/1 | 19/1 | 1.000 | |
| Height (cm) | 162.05 (7.18) | 166.05 (7.24) | 4.00 (-0.62, 8.62) | 0.087 |
| Weight (kg) | 62.35 (6.30) | 63.40 (6.62) | 1.05 (-3.09, 5.19) | 0.610 |
| BMI (kg/m2) | 24.32 (1.54) | 23.97 (1.64) | -0.34 (-1.36, 0.68) | 0.184 |
BMI: Body mass index; SD: Standard deviation
Table 2.
Comparison of gastric volume (ml) over time
| Gastric volume (ml) | Group I Mean (SD) | Group II Mean (SD) | Mean difference (95% Confidence interval) | P |
|---|---|---|---|---|
| T0 | 18.57 (13.05) | 15.28 (12.21) | -3.29 (-11.38, 4.8) | 0.416 |
| T1 | 94.47 (39.09) | 92.97 (34.84) | -1.51 (-25.21, 22.19) | 0.904 |
| T2 | 67.38 (24.52) | 55.31 (24.05) | -12.07 (-27.62, 3.48) | 0.124 |
| T3 | 56.52 (20.91) | 26.83 (17.03) | -29.69 (-41.9, -17.48) | <0.001 |
| T4 | 32.30 (13.20) | 20.80 (15.36) | -11.50 (-20.67, -2.33) | 0.015 |
T0: Baseline before feed; T1: 15 min after feed; T2: 1 h after feed; T3: 2 h after feed; T4: 4 h after feed; SD: Standard deviation
Table 3.
Number of patients having delayed gastric emptying (GER <45%)
| Delayed gastric emptying (GER <45%) | Group I n (%) | Group II n (%) | P |
|---|---|---|---|
| Yes | 16 (80%) | 2 (10%) | <0.001 |
| No | 4 (20%) | 18 (90%) | <0.001 |
GER: Gastric emptying rate; n: Number of patients
Table 4.
Comparison of optic nerve sheath diameter between the two groups
| ONSD (mm) | Group I Mean (SD) | Group II Mean (SD) | Mean difference (95% Confidence interval) | P |
|---|---|---|---|---|
| T0 | 5.20 (0.25) | 4.32 (0.34) | -0.88 (-1.07, -1.69) | <0.001 |
| T1 | 5.28 (0.21) | 4.34 (0.31) | -0.95 (-1.12, -0.78) | <0.001 |
| T2 | 5.26 (0.23) | 4.32 (0.31) | -0.93 (-1.1, -0.76) | <0.001 |
| T3 | 5.2 (0.23) | 4.32 (0.31) | -0.90 (-1.07, -0.73) | <0.001 |
| T4 | 5.20 (0.23) | 4.28 (0.29) | -0.92 (-1.09, -0.75) | <0.001 |
ONSD: Optic Nerve Sheath Diameter; T0: Baseline before feed; T1: 15 min after feed; T2: 1 h after feed; T3: 2 h after feed; T4: 4 h after feed; SD: Standard deviation
Figure 2.
Correlation of gastric emptying rate with optic nerve sheath diameter
DISCUSSION
We observed that gastric emptying was significantly delayed in group I as compared to group II (P < 0.001) and ONSD was significantly higher in group I as compared to group II with a statistically significant negative correlation between ONSD and GER in the entire sample by univariate analysis (P < 0.001).
With the advent of the portable ultrasound machines, gastric emptying can easily be assessed non-invasively.[11] The GER is a measure of the speed of delivery of gastric contents into the duodenum.[12] Delayed gastric emptying is defined as GER <45%, where GER was expressed as the percentage reduction in antral cross-sectional area from 15 to 90 min in a study conducted by Darwiche et al.[10]
Ali et al.[13] conducted a study to compare GETs of fluids with different caloric and nutrient contents in 18 healthy volunteers using ultrasound after the ingestion of four beverages on different occasions. They noted the mean gastric volume at baseline was 65 ml. The gastric volumes increased after the ingestion of beverages at 1 h and then decreased over time, and total emptying was observed at 4 h. The baseline values were higher from our study, maybe because they allowed clear fluids up to 2 h before the surgery while we ensured 6 h fasting in our study. We also observed the increase in gastric volume after feed over time, but total emptying was not there in 4 h. This difference may be due to the inclusion of healthy subjects in their study as opposed to ICU patients in our study.
Kao et al.[6] conducted a study to evaluate the gastric emptying half-time (GET1/2) of liquid meals in 35 patients with moderate to severe head injury by practical radionuclide imaging techniques. The control group included 16 healthy ambulatory subjects. GET1/2 was significantly prolonged in patients with head injury (57.2 ± 20.8 min) as compared to healthy volunteers (29.4 ± 3.7 min) (P < 0.05). This is similar to that observed in our study, where gastric emptying was delayed in patients with head injury.
No previous study observed any correlation between ONSD and GER. ONSD values were significantly higher in head injury patients in our study, indicating raised ICP in these patients. The values of ONSD observed in our study correlate with those of previous studies.[14,15] It has been postulated that traumatic brain injury can result in gastric intrinsic neural dysfunction by reduction in the number of interstitial cells of Cajal leading to gastroparesis in these patients.[16,17] Gut motility is affected in patients with raised ICP due to hyperactivity of parasympathetic and sympathetic systems at different times. Also, raised ICP suppresses the gastric and duodenal contractions by more than 80% and 60%, respectively.[18]
Most of the studies were done in healthy volunteers or patients accepting oral feeds, while our study comprised ICU patients, and ryle’s tube feed was administered. Plain water was selected as feed because it can easily be detected on ultrasonography and ryle’s tube challenge is usually given in the form of water. Patients in ICU were on midazolam and fentanyl infusion, and the patients on prokinetics were excluded from our study.
Our study has a few limitations. Patients receiving different feeds might have different gastric emptying depending upon the caloric content, fat, protein concentration, viscosity, and osmolarity of the feed. ICU patients are on different medications which may affect gastric motility directly or indirectly. The sample size was not powered enough to estimate correlation between GER and various other factors.
Multi-centre serial prospective studies with larger sample sizes are warranted to unfold varied aspects of gastric emptying following various feeding regimens and effects of other variables especially in neurosurgical patients. Individualised feeding protocols need to be explored with their impact on patient outcome.
CONCLUSION
Mechanically ventilated patients in ICU who had neurosurgical pathology exhibited delayed gastric emptying as compared to those who had pulmonary pathology. The former also had increased ONSD predicting raised ICP. Furthermore, gastric emptying was significantly affected by ICP.
Thus, estimation of gastric emptying in head injury patients can guide the start of enteral nutrition and formulate feeding protocols in these patients. Also, it will help in ensuring an empty stomach prior to the administration of general anaesthesia.
Study data availability
De-identified data may be requested with reasonable justification from the authors (email to the corresponding author) and shall be shared upon request.
Disclosure of use of artificial intelligence (AI)-assistive or generative tools
The authors declare that no AI tool was used in the during the preparation of this manuscript.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient consented to his/her images and other clinical information to be reported in the journal. The patient understands that his/her name and initials will not be published and due efforts will be made to conceal his/her identity, but anonymity cannot be guaranteed
Conflicts of interest
There are no conflicts of interest.
Funding Statement
Nil.
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