Negative pressure wound therapy for managing the open abdomen in non‐trauma patients

Abstract

Background

Management of the open abdomen is a considerable burden for patients and healthcare professionals. Various temporary abdominal closure techniques have been suggested for managing the open abdomen. In recent years, negative pressure wound therapy (NPWT) has been used in some centres for the treatment of non‐trauma patients with an open abdomen; however, its effectiveness is uncertain.

Objectives

To assess the effects of negative pressure wound therapy (NPWT) on primary fascial closure for managing the open abdomen in non‐trauma patients in any care setting.

Search methods

In October 2021 we searched the Cochrane Wounds Specialised Register, CENTRAL, MEDLINE, Embase, and CINAHL EBSCO Plus. To identify additional studies, we also searched clinical trials registries for ongoing and unpublished studies, and scanned reference lists of relevant included studies as well as reviews, meta‐analyses, and health technology reports. There were no restrictions with respect to language, date of publication, or study setting.

Selection criteria

We included all randomised controlled trials (RCTs) that compared NPWT with any other type of temporary abdominal closure (e.g. Bogota bag, Wittmann patch) in non‐trauma patients with open abdomen in any care setting. We also included RCTs that compared different types of NPWT systems for managing the open abdomen in non‐trauma patients.

Data collection and analysis

Two review authors independently performed the study selection process, risk of bias assessment, data extraction, and GRADE assessment of the certainty of evidence.

Main results

We included two studies, involving 74 adults with open abdomen associated with various conditions, predominantly severe peritonitis (N = 55). The mean age of the participants was 52.8 years; the mean proportion of women was 39.2%. Both RCTs were carried out in single centres and were at high risk of bias.

Negative pressure wound therapy versus Bogota bag

We included one study (40 participants) comparing NPWT with Bogota bag. We are uncertain whether NPWT reduces time to primary fascial closure of the abdomen (NPWT: 16.9 days versus Bogota bag: 20.5 days (mean difference (MD) ‐3.60 days, 95% confidence interval (CI) ‐8.16 to 0.96); very low‐certainty evidence) or adverse events (fistulae formation, NPWT: 10% versus Bogota: 5% (risk ratio (RR) 2.00, 95% CI 0.20 to 20.33); very low‐certainty evidence) compared with the Bogota bag. We are also uncertain whether NPWT reduces all‐cause mortality (NPWT: 25% versus Bogota bag: 35% (RR 0.71, 95% CI 0.27 to 1.88); very low‐certainty evidence) or length of hospital stay compared with the Bogota bag (NPWT mean: 28.5 days versus Bogota bag mean: 27.4 days (MD 1.10 days, 95% CI ‐13.39 to 15.59); very low‐certainty evidence). The study did not report the proportion of participants with successful primary fascial closure of the abdomen, participant health‐related quality of life, reoperation rate, wound infection, or pain.

Negative pressure wound therapy versus any other type of temporary abdominal closure

There were no randomised controlled trials comparing NPWT with any other type of temporary abdominal closure.

Comparison of different negative pressure wound therapy devices

We included one study (34 participants) comparing different types of NPWT systems (Suprasorb CNP system versus ABThera system). We are uncertain whether the Suprasorb CNP system increases the proportion of participants with successful primary fascial closure of the abdomen compared with the ABThera system (Suprasorb CNP system: 88.2% versus ABThera system: 70.6% (RR 0.80, 95% CI 0.56 to 1.14); very low‐certainty evidence). We are also uncertain whether the Suprasorb CNP system reduces adverse events (fistulae formation, Suprasorb CNP system: 0% versus ABThera system: 23.5% (RR 0.11, 95% CI 0.01 to 1.92); very low‐certainty evidence), all‐cause mortality (Suprasorb CNP system: 5.9% versus ABThera system: 17.6% (RR 0.33, 95% CI 0.04 to 2.89); very low‐certainty evidence), or reoperation rate compared with the ABThera system (Suprasorb CNP system: 100% versus ABThera system: 100% (RR 1.00, 95% CI 0.90 to 1.12); very low‐certainty evidence). The study did not report the time to primary fascial closure of the abdomen, participant health‐related quality of life, length of hospital stay, wound infection, or pain.

Authors' conclusions

Based on the available trial data, we are uncertain whether NPWT has any benefit in primary fascial closure of the abdomen, adverse events (fistulae formation), all‐cause mortality, or length of hospital stay compared with the Bogota bag. We are also uncertain whether the Suprasorb CNP system has any benefit in primary fascial closure of the abdomen, adverse events, all‐cause mortality, or reoperation rate compared with the ABThera system. Further research evaluating these outcomes as well as participant health‐related quality of life, wound infection, and pain outcomes is required. We will update this review when data from the large studies that are currently ongoing are available.

Plain language summary

What are the benefits and risks of negative pressure wound therapy for managing the open abdomen in people who are not trauma patients?

Key messages

‐ We do not know if negative pressure wound therapy (NPWT, defined as pressure lower than a given reference pressure, generally causing suction) helps abdominal wounds to heal quicker or reduces potential harmful effects compared with using a Bogota bag (a sterilised fluid bag used for closing abdominal wounds).

‐ We do not know if a Suprasorb CNP system (a type of NPWT) helps abdominal wounds to heal quicker or reduces potential harmful effects compared with using an ABThera system (another type of NPWT).

‐ We do not know if NPWT increases the risk of bowel perforation. Future research should explore healing time, potential unwanted or harmful effects, all‐cause mortality, length of hospital stay, health‐related quality of life, reoperation rate, wound infection, and pain outcomes.

What is an open abdomen?

Sometimes a person's abdomen needs to be left open while it heals after surgery. However, high death rates are associated with leaving the abdomen open after surgery. Managing the open abdomen is a considerable burden for patients and doctors.

How is this managed?

NPWT uses a sealed dressing connected to a vacuum pump to drain fluid from a wound. However, the safety and effectiveness of NPWT as a treatment for open abdomen is still uncertain.

NPWT has been used in recent years to treat non‐trauma patients after abdominal surgery. Non‐trauma patients are people who need surgery for conditions that are not caused by trauma (e.g. abdominal infection, cancer, ischaemia).

What did we want to find out?

We wanted to find out whether NPWT is effective in treating the open abdomen after surgery in non‐trauma patients in any care setting. We wanted to compare NPWT with other treatment methods or other types of NPWT, and we were particularly interested in their effects on the following:

‐ wound closure (how long it took for wounds to close and how many people had wounds that fully closed);

‐ if there were any harmful or unwanted effects (e.g. bowel perforation);

‐ death rate;

‐ participant health‐related quality of life or health status;

‐ length of hospital stay;

‐ reoperation rate;

‐ wound infection; and

‐ pain.

What did we do?

We searched for studies that compared NPWT with any other type of temporary abdominal closure in non‐trauma patients with open abdomen. We also included studies that compared different types of NPWT systems for managing the open abdomen in non‐trauma patients. We had no restrictions with respect to language, date of publication, or where the study was conducted. We rated our confidence in the evidence, based on factors such as study methods and sizes.

What did we find?

We found one single‐centre study conducted in Turkey, which included 40 adults with open abdomen. Participants were randomly allocated to treatment with either NPWT or a Bogota bag. We cannot tell from the results whether when compared to Bogota bag, NPWT reduces:

‐ the time needed for wounds to completely close;

‐ harmful or unwanted effects (bowel perforation);

‐ death rate; or

‐ length of hospital stay between the groups.

The study did not report the proportion of people with wounds that were successfully closed, participant health‐related quality of life, reoperation rate, wound infection, or pain.

We found another single‐centre study, which was conducted in Austria and included 34 adults with open abdomen. Participants were randomly allocated to treatment with either a Suprasorb CNP system or an ABThera system. We cannot tell from the results whether when compared to an ABThera system, a Suprasorb CNP system reduces:

‐ the proportion of people with wounds that were successfully closed;

‐ harmful or unwanted effects (bowel perforation);

‐ death rate; or

‐ reoperation rate between the groups.

The study did not report the time needed for wounds to completely close, participant health‐related quality of life, length of hospital stay, wound infection, or pain.

What are the limitations of the evidence?

We only found two relevant studies, so we are uncertain about the benefits or harms of using NPWT compared with using a Bogota bag or different types of NPWT systems. We did not find any studies that compared NPWT with other types of temporary abdominal closure.

How up to date is this evidence?

The evidence is up to date to October 2021.

Summary of findings

Summary of findings 1. NPWT compared with the Bogota bag for managing the open abdomen in non‐trauma patients.

NPWT compared with the Bogota bag for managing the open abdomen in non‐trauma patients
Patient or population: adults with an open abdomen after surgery who have not experienced trauma Setting: hospital Intervention: NPWT Comparison: Bogota bag
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with Bogota bag	Risk with NPWT
Time to primary fascial closure of the abdomen Follow‐up: 60 days	The mean time to primary fascial closure of the abdomen was 20.5 days.	The mean time to primary fascial closure of the abdomen was 16.9 days.	MD 3.6 days lower (8.16 lower to 0.96 higher)	40 (1 study)	⊕⊝⊝⊝ Very low1	Uncertain evidence on the effect of NPWT on time to primary fascial closure of the abdomen compared with the Bogota bag
Proportion of participants with successful primary fascial closure of the abdomen Follow‐up: 60 days	Not reported
Adverse events (fistulae formation) Follow‐up: 60 days	Study population		RR 2.00 (0.20 to 20.33)	40 (1 study)	⊕⊝⊝⊝ Very low2	Uncertain evidence on the effect of NPWT on adverse events (fistulae formation) compared with the Bogota bag
	50 per 1000	100 per 1000 (10 to 1000)
All‐cause mortality Follow‐up: 60 days	Study population		RR 0.71 (0.27 to 1.88)	40 (1 study)	⊕⊝⊝⊝ Very Low3	Uncertain evidence on effect of NPWT on all‐cause mortality compared with the Bogota bag
	350 per 1000	248 per 1000 (95 to 658)
Participant health‐related quality of life Follow‐up: 60 days	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; RR: Risk ratio; MD: Mean difference; NPWT: Negative pressure wound therapy.
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.

¹We downgraded the evidence twice for very serious risk of bias in the domains of random sequence generation, allocation concealment, and blinding of outcome assessment; once for serious indirectness (33 non‐trauma patients and 7 trauma patients); and twice for very serious imprecision due to small sample size and wide confidence intervals.
²We downgraded the evidence twice for very serious risk of bias in the domains of random sequence generation, allocation concealment, and blinding of outcome assessment; once for serious indirectness (33 non‐trauma patients and 7 trauma patients); and twice for very serious imprecision because of small sample size and wide confidence intervals.
³We downgraded the evidence once for serious indirectness (33 non‐trauma patients and 7 trauma patients) and twice for very serious imprecision because of small sample size and wide confidence intervals. We did not downgrade for risk of bias because we considered this an objective outcome, which is unlikely to be affected by performance bias and detection bias.

Summary of findings 2. Suprasorb CNP system compared with the ABThera system for managing the open abdomen in non‐trauma patients.

Suprasorb CNP system compared with the ABThera system for managing the open abdomen in non‐trauma patients
Patient or population: adults with an open abdomen after surgery who have not experienced trauma Setting: hospital Intervention: Suprasorb CNP system Comparison: ABThera system
Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	Number of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with ABThera system	Risk with Suprasorb CNP system
Time to primary fascial closure of the abdomen Follow‐up: 60 days	Not reported
Proportion of participants with successful primary fascial closure of the abdomen Follow‐up: 60 days	Study population		RR 0.80 (0.56 to 1.14)	34 (1 study)	⊕⊝⊝⊝ Very low1	Uncertain evidence on effect of the Suprasorb CNP system on proportion of participants with successful primary fascial closure of the abdomen compared with the ABThera system
	882 per 1000	706 per 1000 (494 to 1000)
Adverse events (fistulae formation) Follow‐up: 60 days	Study population		RR 0.11 (0.01 to 1.92)	34 (1 study)	⊕⊝⊝⊝ Very low2	Uncertain evidence on the effect of the Suprasorb CNP system on adverse events (fistulae formation) compared with the ABThera system
	235 per 1000	26 per 1000 (2 to 452)
All‐cause mortality Follow‐up: 60 days	Study population		RR 0.33 (0.04 to 2.89)	34 (1 study)	⊕⊝⊝⊝ Very low3	Uncertain evidence on the effect of the Suprasorb CNP system on all‐cause mortality compared with the ABThera system
	176 per 1000	58 per 1000 (7 to 510)
Participant health‐related quality of life Follow‐up: 60 days	Not reported
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; RR: Risk ratio; MD: Mean difference.
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.

¹We downgraded the evidence twice for very serious risk of bias in the domains of blinding of outcome assessment and other potential sources of bias, once for serious indirectness (31 non‐trauma patients and 3 trauma patients), and twice for very serious imprecision because of small sample size and wide confidence intervals.
²We downgraded the evidence twice for very serious risk of bias in the domains of blinding of outcome assessment and other potential sources of bias, once for serious indirectness (31 non‐trauma patients and 3 trauma patients), and twice for very serious imprecision because of small sample size and wide confidence intervals.
³We downgraded the evidence once for serious risk of bias in the domain of other potential sources of bias, once for serious indirectness (31 non‐trauma patients and 3 trauma patients), and twice for very serious imprecision because of small sample size and wide confidence intervals. We did not downgrade for lack of blinding because we considered this an objective outcome, which is unlikely to be affected by performance bias and detection bias.

Background

Description of the condition

About 143 million surgical procedures are performed worldwide each year to save lives and prevent disability (Meara 2015). Although the exact number of abdominal operations performed annually worldwide is unknown, about 1,313,000 abdominal operations are performed each year in the UK, 6.1 million in the USA, 478,000 in Japan, and 1 million in France (Carney 2017; Fingerhut 1998; Miyata 2018; NHS Digital 2018). After these operations, the abdominal walls in some people may be left open because of the risk of intra‐abdominal hypertension (pressure) (Cirocchi 2013; Fitzpatrick 2017; Friese 2012).

Leaving the abdomen open allows the abdominal contents to expand in order to reduce intra‐abdominal pressure and related complications (Beckman 2016; Fitzpatrick 2017). Although the reasons for leaving the abdomen open vary in different geographical regions, the two most common indications are management of severe peritonitis (abdominal infection) and damage control surgery (a form of surgery typically performed by trauma surgeons in case of severe unstable injuries) for abdominal trauma (Atema 2015; Coccolini 2017a; Fernández 2016; Hofmann 2017; Sartelli 2015). People with an open abdomen are often critically ill and require treatment in the intensive care unit (Acosta 2017; Beckman 2016). 

Management of the open abdomen is a considerable burden for patients and healthcare professionals, and having an open abdomen is associated with high mortality (Acosta 2017; Beckman 2016; Hofmann 2017; Seternes 2017). The reported mortality rate ranges from 21% to 55% in different studies (Acosta 2017; Fortelny 2014; Hofmann 2017; Rausei 2018). The main cause of death in these patients is multiple organ dysfunction syndrome (Boele van Hensbroek 2016; Mayr 2006). Having an open abdomen may also be associated with serious complications, such as severe fluid and heat loss, bowel fistulae formation (an opening connecting the bowel to the body surface or to another hollow organ), loss of abdominal wall domain, and development of incisional hernia (the abnormal exit of tissue or an organ through the wall of the cavity caused by an incompletely healed surgical wound) (Beckman 2016; Chiara 2016; Demetriades 2014). The best way to prevent or reduce these complications is to close the abdomen as soon as possible (Chiara 2016; Cristaudo 2017a; Demetriades 2014; Hofmann 2017). If abdominal closure is not possible, one effective method is to close the abdominal wall temporarily (Chiara 2016; Cristaudo 2017a; Demetriades 2014). The ideal method of temporary abdominal closure should protect abdominal contents, prevent further contamination and intra‐abdominal hypertension, remove any infected fluid, limit infection, facilitate reoperation, preserve abdominal wall tissue, avoid fascial edge retraction, facilitate nursing care, and promote successful abdominal closure. The method should also be inexpensive and cost‐effective (Chiara 2016; Cristaudo 2017b; Demetriades 2014; Kreis 2013; Rogers 2018).

Description of the intervention

Various temporary abdominal closure techniques have been suggested for managing the open abdomen, such as the Bogota bag, which is a sterilised intravenous fluid bag sutured to the fascia (a sheet of connective tissue covering, supporting, or binding together internal organs or parts of the body) to allow the abdominal contents to expand; the Wittmann patch, which involves the use of two opposing sheets sutured to the lateral fascia (a sheet of connective tissue situated at or on the side) to facilitate reoperation; sterilised zipper; and synthetic mesh (Chiara 2016; Cuesta 1991; Demetriades 2014; Kreis 2013; Poortmans 2020; Quyn 2012; Wittmann 1993). Each technique has advantages and disadvantages, but the ultimate goal is to achieve primary fascial closure (full fascia‐to‐fascia closure and complete wound closure) (Atema 2015; Cristaudo 2017b; Demetriades 2014; Quyn 2012).

In recent years, negative pressure wound therapy (NPWT) has been introduced as an alternative for the treatment of critically ill people with an open abdomen (Bruhin 2014; Carlson 2013; Demetriades 2014; Hofmann 2017). NPWT is a device that uses a vacuum dressing and suction pump (negative pressure) to promote wound management and healing (Chiara 2016; Demetriades 2014; Dumville 2014; Dumville 2015; Kreis 2013; Liu 2018; Norman 2020; Rogers 2018). Several different commercial and non‐commercial products are available for NPWT (Bruhin 2014; Dumville 2014; Dumville 2015; Liu 2018; Norman 2020). The most commonly used NPWT systems are the Barker vacuum pack, the vacuum‐assisted closure (V.A.C., KCI, San Antonio, TX), the ABThera system (Abdomen Negative Pressure Therapy System, KCI, San Antonio, TX), and the Suprasorb CNP system (Lohmann & Rauscher, United Arab Emirates) (Auer 2021; Demetriades 2014; Fitzpatrick 2017; Montori 2017; Norman 2020). The cost of commercial NPWT systems varies but is relatively high. For example, each ABThera device costs approximately USD 350 in the USA (Frazee 2013). It is estimated that Medicare payments for NPWT systems increased from USD 24 million to USD 164 million (an increase of almost 583%) in the USA between 2001 and 2007 (HHS 2009).

How the intervention might work

NPWT use for the management of open abdomen wounds involves a porous dressing that covers the abdominal contents, with a membrane between the dressing and the abdominal contents (NICE 2013). Another perforated adhesive membrane is used to cover the entire wound and surrounding skin, and this is attached to a suction system with a drainage tube (Liu 2018; Dumville 2014; Dumville 2015; NICE 2013; Norman 2020). The suction system, using negative pressure, removes fluid and infectious materials from the open abdomen (KCI Medical 2020). NPWT may potentially facilitate wound healing and management of the open abdomen by several different mechanisms. First, the porous dressing may help to isolate the abdominal contents from the abdominal wall and external environment. Second, the negative pressure may actively remove fluid, help to reduce oedema (an excessive accumulation of fluid in the spaces within the tissue), and prevent intra‐abdominal hypertension. Third, the pressure effect is proposed to promote cellular migration and growth of new blood vessels. Finally, it may provide medial tension, which may help to minimise fascial retraction and facilitate the achievement of primary closure (NICE 2013).

Why it is important to do this review

The use of NPWT for managing the open abdomen is controversial (Atema 2015; Coccolini 2017b; Coccolini 2018; Sartelli 2015). NPWT may potentially benefit people in terms of reduced mortality and successful primary fascial closure; conversely, it may have no benefits and could even lead to adverse effects, such as increasing the risk of bowel fistulae formation (Carlson 2013; Giudicelli 2017; Hofmann 2017). The National Institute for Health and Care Excellence (NICE) in the UK published guidance about NPWT for the open abdomen in 2013 (NICE 2013). NICE concluded that evidence was adequate to support the use of NPWT for the open abdomen, but also encouraged more research on this issue (NICE 2013). One Cochrane Review has assessed the role of NPWT in open traumatic wounds (Iheozor‐Ejiofor 2018). The protocol for our review was originally published in 2016 (Boele van Hensbroek 2016); we published a new version in 2020 (Cheng 2020). The aim of our review is to inform decision makers and guide future research.

Objectives

To assess the effects of negative pressure wound therapy (NPWT) on primary fascial closure for managing the open abdomen in non‐trauma patients in any care setting.

Methods

Criteria for considering studies for this review

Types of studies

Eligible studies were randomised controlled trials (RCTs), including cluster RCTs. We intended to include studies reported as full text or published as abstract only, as well as unpublished data. We excluded cross‐over trials as they are not an appropriate design in this context. We excluded quasi‐randomised trials and non‐randomised studies.

Types of participants

Eligible trials were those involving adults managed in any care setting that used NPWT for the management of the open abdomen that was not caused by trauma. Trials involving both trauma and non‐trauma patients were eligible only if the results for non‐trauma patients were presented separately and randomisation was stratified by trauma and non‐trauma, or if 75% or more of the participants in the trial were non‐trauma patients. We would have excluded people who underwent abdominal wall correction months or years after initial management of the open abdomen because in these cases the open abdomen is not treated during the first admission. Trials recruiting participants at first and subsequent hospital admissions were eligible only if the results for the first admission were presented separately and randomisation was stratified by first and subsequent treatments, or if 75% or more of the participants in the trial were first‐admission patients.

Types of interventions

The primary intervention was NPWT delivered by any mode. We planned to assess the following comparisons for people with an open abdomen not caused by trauma:

• NPWT (both commercial and non‐commercial products) versus an alternative method of temporary abdominal closure (e.g. Bogota bag, Wittmann patch, sterilised zipper, or synthetic mesh); and

• one type of NPWT system versus a different type of NPWT system.

We only included RCTs in which the use of a specific NPWT intervention during the treatment period was the only systematic difference between treatment groups.

Types of outcome measures

We list primary and secondary outcomes below. If a study was otherwise eligible (e.g. correct study design, population, intervention, and comparator) but did not report a listed outcome, we contacted the study authors when possible to establish whether an outcome of interest was measured but not reported. If the study authors had replied and stated that none of the outcomes were measured in their study, we would have included the study and discussed the potential of selective outcome reporting.

We reported outcome measures at the latest time point available (assumed to be the length of follow‐up if not specified) and the time point specified in the study methods as being of primary interest (if this was different from the latest time point available). If data had allowed, we would have used the latest time point available for the primary analysis and used the time point specified in the methods as being of primary interest as a sensitivity analysis. For all outcomes, we classed assessment of outcome measures from:

• less than one week to eight weeks as short term;

• greater than eight weeks to 26 weeks as medium term; and

• greater than 26 weeks as long term.

Primary outcomes

• Primary fascial closure of the abdomen

• Adverse events

Primary fascial closure

We defined primary fascial closure as full fascia‐to‐fascia closure and complete wound closure after open abdominal treatment during index admission (hospital admission during which open abdominal treatment was started). We also accepted authors' definitions of primary fascial closure. For this review, we regarded the following as providing the most relevant and rigorous measures of outcome:

• time to primary fascial closure of the abdomen (we recorded whether or not censored data had been appropriately analysed and listed any adjustment factors); and

• proportion of participants with successful primary fascial closure of the abdomen (frequency of primary fascial closure) at a particular time point.

If both of the outcomes above had been reported, we would have presented all data in a summary outcome table for reference, but focused on reporting time to primary fascial closure. We accepted the authors' definitions of what constituted primary fascial closure. Time to primary fascial closure was our preferred measure; however, we did not expect it to be reported in many studies.

Adverse events

Adverse events where a clear methodology for the collection of adverse event data was provided. These included fistulae formation, hernia formation, intra‐abdominal abscess, and failure to maintain negative pressure. We reported the number of participants in each group with an event.

Secondary outcomes

• All‐cause mortality

• Participant health‐related quality of life or health status (measured using a standardised generic questionnaire such as EuroQol‐5D (EQ‐5D); 36‐item, 12‐item, or 6‐item Short Form (SF‐36, SF‐12, or SF‐6); or wound‐specific questionnaires such as the Cardiff Wound Impact Schedule (CWIS)). We did not include ad hoc measures of quality of life that were not likely to be validated and would not be common to multiple trials.

• Length of hospital stay

• Reoperation rate

• Wound infection: as defined by study authors (number of participants in each group with wound infection)

• Pain (measured using survey or questionnaire or data capture process or visual analogue scale)

Search methods for identification of studies

Electronic searches

We searched the following electronic databases to identify reports of relevant clinical trials:

• Cochrane Wounds Specialised Register (searched 4 October 2021);

• Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library searched via the Cochrane Register of Studies (searched 4 October 2021);

• MEDLINE Ovid including In‐Process & Other Non‐Indexed Citations (1946 to 4 October 2021);

• Embase Ovid (1974 to 4 October 2021); and

• CINAHL EBSCO Plus (Cumulative Index to Nursing and Allied Health Literature; 1937 to 4 October 2021).

We provide the search strategies for the Cochrane Wounds Specialised Register, CENTRAL, MEDLINE Ovid, Embase Ovid, and CINAHL EBSCO Plus in Appendix 1. In MEDLINE Ovid, we combined the subject‐specific strategy with the sensitivity‐maximising version of the Cochrane highly sensitive search strategy for identifying randomised trials (2008 revision) (Lefebvre 2021). We combined the Embase Ovid search with the Embase Ovid filter developed by Cochrane UK (Lefebvre 2021). We combined the CINAHL EBSCO Plus search with the trial filter developed by Glanville 2019. There were no restrictions with respect to language, date of publication, or study setting.

We also searched the following clinical trials registries:

• US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov (www.clinicaltrials.gov; searched 4 October 2021); and

• World Health Organization International Clinical Trials Registry Platform (www.who.int/clinical-trials-registry-platform; searched 4 October 2021).

In addition, we carried out a separate, more sensitive search designed specifically to identify trial registry records:

• Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library via the Cochrane Register of Studies (searched 4 October 2021).

We provide the search strategies for clinical trial registries in Appendix 1.

Searching other resources

Searching reference lists of included trials and relevant reviews

We identified other potentially eligible trials or ancillary publications by searching the reference lists of retrieved included trials as well as relevant systematic reviews, meta‐analyses, and health technology assessment reports.

Searching by contacting individuals or organisations

When necessary, we contacted authors of key papers and abstracts to request further information about their trials.

Adverse effects

We did not perform a separate search for adverse effects of interventions used; we only considered adverse effects described in included studies.

Data collection and analysis

Selection of studies

Two review authors (KW, JG) independently assessed the titles and abstracts of the citations retrieved by the searches for relevance. After this initial assessment, we obtained full‐text copies of all studies that we considered to be potentially relevant. Two review authors (KW, JG) independently checked the full papers for eligibility; disagreements were resolved by discussion and, where required, the input of a third review author (XW). Where required and possible, we contacted study authors where the eligibility of a study was unclear. We recorded all reasons for exclusion of studies for which we had obtained full copies in the 'Characteristics of excluded studies' tables. We completed a PRISMA flowchart to summarise this process (Liberati 2009).

If studies had been reported in multiple publications or reports, we would have obtained all publications and collated the reports so that each study, rather than each report, was the unit of interest for the review, and the study had a single identifier with multiple references. We would have extracted data from all reports to ensure that maximal relevant data were obtained.

Data extraction and management

We extracted and summarised details of the eligible studies using a data extraction sheet. Two review authors (ZL, JG) independently extracted data, resolved disagreements by discussion, and drew on a third review author (XW) where required. Where data were missing from reports, we attempted to contact the study authors to obtain this information. Where we included a study with more than two intervention arms, we only extracted data from intervention and control groups that met the eligibility criteria. If we had included a study with more than two eligible intervention arms, to avoid double‐counting of participants, we would have used either separate comparisons (with different forest plots) or combined intervention groups where we considered this appropriate.

We extracted the following data where possible by treatment group for the prespecified interventions and outcomes in this review and completed a 'Characteristics of included studies' table. We collected the following outcome data for relevant time points as described in Types of outcome measures:

• country of origin;

• type of surgery;

• trial design (e.g. parallel, cluster);

• care setting;

• number of participants randomised to each trial arm;

• eligibility criteria and key baseline participant data;

• size of the wound;

• details of treatment regimen received by each group;

• duration of treatment;

• details of any co‐interventions;

• primary and secondary outcome(s) (with definitions);

• outcome data for primary and secondary outcomes (by group);

• duration of follow‐up;

• number of withdrawals (by group);

• publication status of study; and

• source of funding for trial.

Assessment of risk of bias in included studies

Two review authors (YC, ZZ) independently assessed the included studies using Cochrane's RoB 1 tool (Higgins 2017). This tool addresses six specific domains: sequence generation, allocation concealment, blinding, incomplete data, selective outcome reporting, and other sources of bias. We assessed blinding and completeness of outcome data for each of the review outcomes separately. We noted that since primary fascial closure was a subjective outcome, it was at high risk of measurement bias when outcome assessment was not blinded. We present our assessment of risk of bias using two risk of bias summary figures: a summary of bias for each item across all studies and a summary of bias for each trial across all of the risk of bias items. If we judged a trial to be at low risk of bias in all domains, we considered it to be at low risk of bias overall. We considered trials to be at high risk of bias if we judged them to be at high risk of bias for one or more domains, or if we judged the risk of selection bias or performance and detection bias to be unclear. If we had included trials that used cluster randomisation, we would also have considered the risk of bias in terms of recruitment bias, baseline imbalance, loss of clusters, incorrect analysis, and comparability with individually randomised trials (Higgins 2021a). We would have recorded issues with unit of analysis, for example, where a cluster trial had been undertaken but analysed at the individual level in the study report (Appendix 2).

Assessment of bias in conducting the systematic review

We conducted the review according to our published protocol, Cheng 2020, and reported any deviations from it in Differences between protocol and review.

Measures of treatment effect

For dichotomous outcomes, we calculated the risk ratio (RR) with 95% confidence intervals (CIs). For continuously distributed outcome data, we used the mean difference (MD) with 95% CIs if all trials used the same scale or similar assessment scales. If trials had used different assessment scales, we would have used the standardised mean difference (SMD) with 95% CIs. We considered the mean time to primary fascial closure without survival analysis as a valid outcome because trial authors regarded time to primary fascial closure as a continuous measure (as there was no censoring). We would have reported time‐to‐event data (e.g. time to primary fascial closure) as hazard ratios (HRs) and 95% CIs where possible, in accordance with the methods described in the Cochrane Handbook for Systematic Reviews of Interventions (Deeks 2021). If studies reporting time‐to‐event data (e.g. time to primary fascial closure) did not report an HR, then where feasible, we would have estimated this using other reported outcomes, such as the numbers of events, through the application of available statistical methods (Parmar 1998).

Unit of analysis issues

We expected that the unit of analysis in most trials was one participant with one abdominal wound subjected to one intervention. For such trials, we treated the participant as the unit of analysis when the number of abdominal wounds assessed appeared equal to the number of participants (e.g. abdominal wound per participant). However, we had anticipated that there might have been trials that presented the following two types of unit of analysis issues.

Participants could have had multiple wounds that were all randomised to the same intervention (where all of their abdominal wounds received this intervention), and if the analyses focused on the wound, this would be clustered data (wounds clustered on an individual). We would have recorded where a cluster RCT had been conducted or where a trial contained evidence of clustered data. We would have noted cases of incorrect analyses. We would have recorded this as part of the risk of bias assessment. If possible, we would have approximated the correct analyses based on guidance in the Cochrane Handbook (Higgins 2021b), using the following information:

• the number of clusters (or groups) randomised to each intervention group or the mean size of each cluster;

• the outcome data ignoring the cluster design for the total number of participants (e.g. number or proportion of participants with events or means and standard deviations); and

• an estimate of the intracluster (or intraclass) correlation coefficient (ICC).

If we could not analyse the trial data correctly, we would have extracted and presented outcome data but not analysed them further.

A second alternative scenario could have been trials where individuals had multiple abdominal wounds and abdominal wounds were randomised to different interventions. If this had been the case, we would have noted that randomisation had been undertaken at the abdominal wound level and assessed whether correct paired analysis was performed. If an incorrect analysis was performed and the required data could be accessed by contacting the study authors, we would have tried to approximate a correct analysis. If this was not possible, we would have extracted and presented the relevant outcome data but not analysed or pooled them further (Lesaffre 2009).

Dealing with missing data

It is common for data to be missing from trial reports. Excluding participants postrandomisation from the analysis or ignoring those participants who are lost to follow‐up compromises the randomisation, and potentially introduces bias into the trial. Where there were missing data that we considered should be included in the analyses, we contacted the study authors to request whether these data were available.

If data had remained missing for our outcome 'proportion of participants with successful primary fascial closure of the abdomen', we would have assumed that if randomised participants had not been included in an analysis, their abdominal wound did not close (e.g. they would have been considered in the denominator, but not the numerator).

For continuous variables (e.g. length of hospital stay) and for all secondary outcomes, we presented available data from the study reports or study authors, and did not impute missing data. Where measures of variance were missing, we calculated these wherever possible. If calculation was not possible, we contacted the study authors. Where these measures of variance were not available, we would have excluded the study from any relevant meta‐analyses that we conducted.

Assessment of heterogeneity

Assessment of heterogeneity can be a complex, multi‐faceted process. First, we considered clinical and methodological heterogeneity, that is, the degree to which the included studies varied in terms of participant, intervention, outcome, and characteristics such as length of follow‐up. If appropriate, we would have supplemented this assessment of clinical and methodological heterogeneity by information regarding statistical heterogeneity assessed using the Chi² test (we would have considered a significance level of P < 0.10 to indicate statistically significant heterogeneity) in conjunction with the I² statistic (Higgins 2003). The I² statistic examines the percentage of total variation across RCTs that is due to heterogeneity rather than chance (Higgins 2003). In general, I² values of 25% or less may mean a low level of heterogeneity (Higgins 2003), and values of more than 75% indicate very high heterogeneity (Deeks 2021). If there had been evidence of high heterogeneity, we would have attempted to explore this further: see Data synthesis.

Assessment of reporting biases

Reporting biases arise when the nature and direction of the results influences the dissemination of research findings. Publication bias is one of several possible causes of 'small‐study effects', that is, a tendency for estimates of the intervention effect to be more beneficial in smaller RCTs. Funnel plots allow a visual assessment of whether small‐study effects may be present in a meta‐analysis. A funnel plot is a simple scatter plot of the intervention effect estimates from individual RCTs against some measure of each trial's size or precision (Page 2021). We planned to present funnel plots for meta‐analyses comprising 10 RCTs or more using Review Manager 5 (Review Manager 2020), but we were unable to do this as only two studies met the inclusion criteria for this review.

Data synthesis

We presented details of the included studies in a narrative review according to the type of comparator. We considered clinical and methodological heterogeneity, and we would have undertaken pooling within comparisons if studies had appeared appropriately similar in terms of open abdomen aetiology, intervention type, duration of follow‐up, and outcome type.

We were unable to prespecify the amount of clinical, methodological, and statistical heterogeneity in the included studies, but it might have been extensive. Thus, we anticipated using a random‐effects approach for meta‐analysis. Conducting meta‐analysis with a fixed‐effect model in the presence of even minor heterogeneity might provide overly narrow CIs. We would only have used a fixed‐effect approach when we assessed clinical and methodological heterogeneity to be minimal and the following assumption held: that a single underlying treatment effect was being estimated. We would have used Chi² and I² tests to quantify heterogeneity, but we would not have used these to guide the choice of model for meta‐analysis. We would have exercised caution when meta‐analysed data were at risk of small‐study effects because a random‐effects model might have been unsuitable. In this case, or where there were other reasons to question the selection of a fixed‐effect or random‐effects model, we would have assessed the impact of the approach using sensitivity analyses to compare results from alternate models. We would have reported any evidence that suggested that the use of a particular model might not have been robust. We might have meta‐analysed even when there was thought to be extensive heterogeneity. We would have attempted to explore the causes behind this using meta‐regression, if possible (Thompson 1999).

We presented data using forest plots where possible. For dichotomous outcomes, we presented the summary estimate as a RR with 95% CI. Where continuous outcomes were measured in the same way across studies, we planned to present a pooled MD with 95% CI; we planned to pool SMD estimates where studies measured the same outcome using different methods. For time‐to‐event data, we planned to plot (and, if appropriate, pool) estimates of HRs and 95% CIs as presented in the study reports using the generic inverse variance method in Review Manager 5 (Review Manager 2020). If time to primary fascial closure had been analysed as a continuous measure but it was not clear if the open abdomen had healed, we would have documented the use of the outcome in the study, but would not have summarised the data or used them in any meta‐analysis.

We obtained pooled estimates of the treatment effect using Review Manager 5 (Review Manager 2020).

Subgroup analysis and investigation of heterogeneity

We planned to carry out the following subgroup analyses if there were sufficient studies:

• different methods of temporary abdominal closure in the comparator group (e.g. Bogota bag, Wittmann patch, zipper); and

• different aetiologies (e.g. severe peritonitis, severe acute pancreatitis).

We would have used the following outcomes in subgroup analyses:

• primary fascial closure (time to primary fascial closure and proportion of participants with wound with successful primary fascial closure); and

• adverse events.

We would have explored differences between subgroups using random‐effects meta‐regression, if possible.

We would have used the formal Chi² test for subgroup differences to test for subgroup interactions. We would have compared subgroups using the analysis option 'test for subgroup differences' in Review Manager 5 (Review Manager 2020). However, none of this was possible as we included an insufficient number of studies in the review.

Sensitivity analysis

Where possible and appropriate, we planned to perform sensitivity analyses to explore the effects of the following criteria:

• changing between worst‐case scenario analysis and best‐case scenario analysis for missing data;

• excluding studies in which either the mean or standard deviation, or both, were imputed; and

• using the time point specified in the methods as being of primary interest.

We would have used the following outcomes in sensitivity analyses:

• primary fascial closure (time to primary fascial closure and proportion of participants with wound with successful primary fascial closure); and

• adverse events.

We were unable to carry out sensitivity analyses as an insufficient number of studies were included in the review.

Summary of findings and assessment of the certainty of the evidence

We present the main results of the review in summary of findings tables. These tables present key information concerning the certainty of the evidence, the magnitude of the effects of the interventions examined, and the sum of the available data for the main outcomes (Schünemann 2021a). The summary of findings tables also include an overall grading of the evidence related to each of the main outcomes using the GRADE approach. The GRADE approach defines the certainty of a body of evidence as the extent to which one can be confident that an estimate of effect or association is close to the true quantity of specific interest. The certainty of a body of evidence involves consideration of within‐trial risk of bias (methodological quality), directness of evidence, heterogeneity, precision of effect estimates, and risk of publication bias (Schünemann 2021b). We presented the following outcomes in the summary of findings tables:

• time to primary fascial closure of the abdomen;

• proportion of participants with successful primary fascial closure of the abdomen;

• adverse events;

• all‐cause mortality; and

• participant health‐related quality of life.

We considered the time points and method of outcome measurement specified in Types of outcome measures in the summary of findings tables. When evaluating the risk of bias domain, we downgraded the GRADE assessment only when we classified a study as being at high risk of bias for one or more domains or when the risk of bias assessment for selection bias (generation of the randomisation sequence domain and the allocation concealment domain) was unclear. We downgraded the GRADE assessment when the risk of bias assessment for blinding was unclear (e.g. classified as unclear for the performance bias domain and the detection bias domain) as well as at high risk of bias. We did not downgrade for unclear risk of bias assessments in other domains.

We planned to select an informal optimal information size of 300 for binary outcomes, following the GRADE default value. We also followed GRADE guidance and downgraded twice for serious imprecision when there were very few events and when CIs around effects included both appreciable benefit and appreciable harm.

We based the Methods section of this review on a standard template used by Cochrane Wounds.

Results

Description of studies

See 'Characteristics of included studies', 'Characteristics of excluded studies', and 'Characteristics of ongoing studies' tables.

Results of the search

We identified 585 records through electronic searches of databases and 110 trial registry records. We did not identify any records by scanning reference lists of the identified randomised controlled trials (RCTs). We excluded 681 clearly irrelevant records through reading the titles and abstracts. We retrieved the remaining 14 records for further assessment. We excluded 10 studies for the reasons listed in the 'Characteristics of excluded studies' tables, and we identified two ongoing studies (Kirkpatrick 2018; Rajabaleyan 2019). Only two RCTs fulfilled the inclusion criteria for this review (Auer 2021; Rencüzoğulları 2015). We present the study flow diagram in Figure 1.

1.

Study flow diagram

Included studies

We listed details of the studies in the 'Characteristics of included studies' tables.

Negative pressure wound therapy (NPWT) versus Bogota bag

One study randomised 40 participants with open abdomen (33 non‐trauma patients and 7 trauma patients) to the NPWT group (N = 20) or the Bogota bag group (N = 20). This RCT was a single‐centre study conducted in Turkey (Rencüzoğulları 2015). This RCT did not describe the sample size calculation. The mean age of the participants was 50.9 years, and the mean proportion of women was 42.5%. The size of the wound was comparable between the NPWT group and the Bogota bag group. The outcomes reported were time to primary fascial closure of the abdomen, adverse events (fistulae formation), all‐cause mortality, length of hospital stay, and intra‐abdominal pressure. This study did not report the funding source or any conflicts of interest.

NPWT versus any other type of temporary abdominal closure

We did not identify any randomised controlled trials comparing NPWT to any other type of temporary abdominal closure.

Type of NPWT

One study randomised 34 participants with open abdomen (31 non‐trauma patients and 3 trauma patients) to a type of NPWT (Suprasorb CNP system; N = 17) or another type of NPWT (ABThera system; N = 17). This RCT was a single‐centre study conducted in Austria (Auer 2021). This RCT did describe the sample size calculation. The mean age of the participants was 55.0 years, and the mean proportion of women was 35.3%. The outcomes reported were proportion of participants with successful primary fascial closure of the abdomen, adverse events (fistulae formation), all‐cause mortality, and reoperation rate. A non‐commercial grant funded this study. This study did not report any conflicts of interest.

Excluded studies

We excluded 10 studies, and the details are listed in the 'Characteristics of excluded studies' tables. We excluded four trials because they involved both trauma and non‐trauma patients, and the results for non‐trauma patients were not presented separately or the proportion of non‐trauma participants was larger than the threshold we set (of 25% of participants or less), or both (Bee 2008; Correa 2016; Kirkpatrick 2015; Long 2014). We excluded one trial because the use of NPWT during the treatment period was not the only systematic difference between treatment groups. The primary intervention in this study was retentions sutured sequential fascial closure (a method of temporary abdominal closure) rather than NPWT (Pliakos 2010). We excluded the remaining studies because they were not randomised controlled trials (Barker 2000; Fortelny 2014; Kurt 2021; Perathoner 2010; Villalobos 2020).

Ongoing studies

Kirkpatrick 2018: 550 participants with severe complicated intra‐abdominal sepsis will be randomised to NPWT management or closed abdomen management. This trial is currently recruiting participants; it is being performed in Canada and began in May 2017. The primary outcome is the rate of survival of participants. The secondary outcomes are the length of days in the intensive care unit and the concentrations of blood IL‐6 ('Characteristics of ongoing studies' tables).

Rajabaleyan 2019: 320 participants with faecal or diffuse peritonitis will be randomised to NPWT management or closed abdomen management. This trial has not yet recruited participants; it is being performed in Canada and began in April 2019. The primary outcome is peritonitis‐related complications. The secondary outcomes are quality of life, ventral hernia rate, and cost‐effective analysis ('Characteristics of ongoing studies' tables).

Risk of bias in included studies

Figure 2 and Figure 3 show the risk of bias of the included studies. Both studies were at high risk of bias (Auer 2021; Rencüzoğulları 2015).

2.

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies

3.

Risk of bias summary: review authors' judgements about each risk of bias item for each included study

Allocation

We judged random sequence generation and allocation concealment to be at low risk of bias in one study (Auer 2021). Random sequence generation and allocation concealment were at unclear risk of bias for the second study: the paper provided no specific information, and there was no response to our queries from the study authors (Rencüzoğulları 2015).

Blinding

Due to the nature of the interventions, performing surgeons could not be blinded to group allocation in either study (Auer 2021; Rencüzoğulları 2015). We therefore judged both studies to be at high risk of bias for blinding of participants and personnel. However, it should be possible to ensure blinding of outcome assessors. The study authors stated that both studies could not be defined as blinded (Auer 2021; Rencüzoğulları 2015). Thus, we judged that blinding of outcome assessment was also at high risk of bias for both studies.

Incomplete outcome data

There were no postrandomisation dropouts in either study (Auer 2021; Rencüzoğulları 2015). Thus, we considered both studies to be at low risk of attrition bias.

Selective reporting

The study protocols were not available for either study, but both studies included results for key outcomes that would be expected to have been reported for such studies (Auer 2021; Rencüzoğulları 2015). Thus, we judged that selective reporting was at low risk of bias for both studies.

Other potential sources of bias

Baseline imbalance was at high risk of bias for one study (Auer 2021). Baseline imbalance was at low risk of bias for the other study (Rencüzoğulları 2015).

Effects of interventions

See: Table 1; Table 2

NPWT versus Bogota bag (1 study: 40 participants)

Time to primary fascial closure of the abdomen

Rencüzoğulları 2015 reported time to primary fascial closure of the abdomen. It is uncertain if there is a difference between NPWT and the Bogota bag in terms of mean time to primary fascial closure of the abdomen (Analysis 1.1). We graded the available evidence to be of very low certainty; we downgraded twice for very serious risk of bias (unclear risk of random sequence generation and allocation concealment and high risk of bias for blinding of outcome assessment), once for serious indirectness (33 non‐trauma participants and 7 trauma participants), and twice for very serious imprecision (small sample size and wide confidence interval) (Table 1). The mean (standard deviation (SD)) time to primary fascial closure of the abdomen in the NPWT group was 16.9 (3.2) days, and the mean (SD) time to primary fascial closure of the abdomen in the Bogota bag group was 20.5 (9.9) days (mean difference (MD) ‐3.60 days, 95% confidence interval (CI) ‐8.16 to 0.96 days). However, this study did not report whether all of the participants reached primary fascial closure, and there was no response to our queries from the study authors, so we cannot be sure of the reliability of these data.

1.1. Analysis.

Comparison 1: NPWT versus Bogota bag, Outcome 1: Time to primary fascial closure of the abdomen

Proportion of participants with successful primary fascial closure of the abdomen

The study did not report this outcome.

Adverse events

Rencüzoğulları 2015 reported fistulae formation as an adverse event. It is uncertain if there is a difference between NPWT and the Bogota bag in terms of fistulae formation (Analysis 1.2). We assessed the evidence as being of very low certainty; we downgraded twice for very serious risk of bias (unclear risk of random sequence generation and allocation concealment and high risk of bias for blinding of outcome assessment), once for serious indirectness (33 non‐trauma patients and 7 trauma patients), and twice for very serious imprecision (small sample size and wide confidence intervals) (Table 1). The fistulae formation rate was 10% in the NPWT group (N = 2) and 5% in the Bogota bag group (N = 1) (risk ratio (RR) 2.00, 95% CI 0.20 to 20.33).

1.2. Analysis.

Comparison 1: NPWT versus Bogota bag, Outcome 2: Adverse events

All‐cause mortality

Rencüzoğulları 2015 reported all‐cause mortality. It is uncertain if there is a difference between NPWT and the Bogota bag in terms of all‐cause mortality (Analysis 1.3). We assessed the evidence as being of very low certainty; we downgraded once for serious indirectness (33 non‐trauma patients and 7 trauma patients) and twice for very serious imprecision (small sample size and wide confidence intervals). We did not downgrade the certainty of evidence for all‐cause mortality for risk of bias because it was unlikely to be affected by performance bias and detection bias (Table 1). The all‐cause mortality was 25% in the NPWT group (N = 5) and 35% in the Bogota bag group (N = 7) (RR 0.71, 95% CI 0.27 to 1.88).

1.3. Analysis.

Comparison 1: NPWT versus Bogota bag, Outcome 3: All‐cause mortality

Participant health‐related quality of life or health status

The study did not report this outcome.

Length of hospital stay

Rencüzoğulları 2015 reported length of hospital stay. It is uncertain if there is a difference between NPWT and the Bogota bag in terms of length of hospital stay (Analysis 1.4). We assessed the evidence as being of very low certainty; we downgraded twice for very serious risk of bias (unclear risk of random sequence generation and allocation concealment and high risk of bias for blinding of outcome assessment), once for serious indirectness (33 non‐trauma patients and 7 trauma patients), and twice for very serious imprecision (small sample size and wide confidence intervals). The mean (SD) length of hospital stay was 28.5 (21.3) days for the NPWT group and 27.4 (25.3) days for the Bogota bag group (MD 1.10 days, 95% CI ‐13.39 to 15.59).

1.4. Analysis.

Comparison 1: NPWT versus Bogota bag, Outcome 4: Length of hospital stay

Reoperation rate

The study did not report this outcome.

Wound infection

The study did not report this outcome.

Pain

The study did not report this outcome.

NPWT versus any other type of temporary abdominal closure

There were no randomised controlled trials comparing NPWT with any other type of temporary abdominal closure.

Comparison of different NPWT devices (1 study: 34 participants)

One study compared a type of NPWT (Suprasorb CNP system) with another type of NPWT (ABThera system) for managing the open abdomen (Auer 2021).

Time to primary fascial closure of the abdomen

The study did not report this outcome.

Proportion of participants with successful primary fascial closure of the abdomen

Auer 2021 reported proportion of participants with successful primary fascial closure of the abdomen. It is uncertain if there is a difference between the Suprasorb CNP system and the ABThera system in terms of proportion of participants with successful primary fascial closure of the abdomen (Analysis 2.1). We assessed the evidence as of very low certainty; we downgraded twice for very serious risk of bias (high risk of bias for blinding of outcome assessment and baseline imbalance), once for serious indirectness (31 non‐trauma patients and 3 trauma patients), and twice for very serious imprecision (small sample size and wide confidence intervals) (Table 2). The proportion of participants with successful primary fascial closure of the abdomen was 88.2% in the Suprasorb CNP group (N = 15) and 70.6% in the ABThera group (N = 12) (RR 0.80, 95% CI 0.56 to 1.14).

2.1. Analysis.

Comparison 2: Suprasorb CNP system versus ABThera system, Outcome 1: Proportion of participants with successful primary fascial closure of the abdomen

Adverse events

Auer 2021 reported fistulae formation as an adverse event. It is uncertain if there is a difference between the Suprasorb CNP system and the ABThera system in terms of fistulae formation (Analysis 2.2). We assessed the evidence as of very low certainty; we downgraded twice for very serious risk of bias (high risk of bias for blinding of outcome assessment and baseline imbalance), once for serious indirectness (31 non‐trauma patients and 3 trauma patients), and twice for very serious imprecision (small sample size and wide confidence intervals) (Table 2). The fistulae formation rate was 0% in the Suprasorb CNP group (N = 0) and 23.5% in the ABThera group (N = 4) (RR 0.11, 95% CI 0.01 to 1.92).

2.2. Analysis.

Comparison 2: Suprasorb CNP system versus ABThera system, Outcome 2: Adverse events

All‐cause mortality

Auer 2021 reported all‐cause mortality. It is uncertain if there is a difference between the Suprasorb CNP system and the ABThera system in terms of all‐cause mortality (Analysis 2.3). We assessed the evidence as of very low certainty; we downgraded once for serious risk of bias (baseline imbalance), once for serious indirectness (31 non‐trauma patients and 3 trauma patients), and twice for very serious imprecision (small sample size and wide confidence intervals). We did not downgrade the certainty of evidence for all‐cause mortality for lack of blinding because this is considered an objective outcome, which is unlikely to be affected by performance bias and detection bias (Table 2). The all‐cause mortality was 5.9% in the Suprasorb CNP group (N = 1) and 17.6% in the ABThera group (N = 3) (RR 0.33, 95% CI 0.04 to 2.89).

2.3. Analysis.

Comparison 2: Suprasorb CNP system versus ABThera system, Outcome 3: All‐cause mortality

Participant health‐related quality of life or health status

The study did not report this outcome.

Length of hospital stay

The study did not report this outcome.

Reoperation rate

Auer 2021 reported reoperation rate. It is uncertain if there is a difference between the Suprasorb CNP system and the ABThera system in terms of reoperation rate (Analysis 2.4). We assessed the evidence as of very low certainty; we downgraded twice for very serious risk of bias (high risk of bias for blinding of outcome assessment and baseline imbalance), once for serious indirectness (31 non‐trauma patients and 3 trauma patients), and once for serious imprecision (small sample size). The reoperation rate was 100% in the Suprasorb CNP group (N = 17) and 100% in the ABThera group (N = 17) (RR 1.00, 95% CI 0.90 to 1.12).

2.4. Analysis.

Comparison 2: Suprasorb CNP system versus ABThera system, Outcome 4: Reoperation rate

Wound infection

The study did not report this outcome.

Pain

The study did not report this outcome.

Subgroup analysis

We did not perform any of the planned subgroup analyses because this review included only two studies.

Sensitivity analysis

We did not perform any of the planned sensitivity analyses because this review included only two studies.

Discussion

Summary of main results

Evidence from two studies, with a total of 74 participants with open abdomen, contributed data to the outcomes of interest for this review.

One study (40 participants) compared negative pressure wound therapy (NPWT) with a Bogota bag for managing the open abdomen in 33 non‐trauma patients and 7 trauma patients. We are uncertain whether there were differences between NPWT and the Bogota bag in terms of primary fascial closure of the abdomen, adverse events, all‐cause mortality, or length of hospital stay. The study did not report the proportion of participants with successful primary fascial closure of the abdomen, participant health‐related quality of life, reoperation rate, wound infection, or pain. Another study (34 participants) compared different types of NPWT systems (Suprasorb CNP system versus ABThera system) for managing the open abdomen in 31 non‐trauma patients and 3 trauma patients. We are uncertain whether there were differences between these systems in terms of primary fascial closure of the abdomen, adverse events, all‐cause mortality, or reoperation rate. The study did not report the time to primary fascial closure of the abdomen, participant health‐related quality of life, length of hospital stay, wound infection, or pain. These results were based on very low‐certainty evidence, which we downgraded for risk of bias, indirectness, and imprecision.

We did not identify any randomised controlled trials comparing NPWT with any other type of temporary abdominal closure.

Overall completeness and applicability of evidence

The study included 74 adults with open abdomen for various diseases, including severe peritonitis (N = 55), malignancy (N = 9), and trauma (N = 10). The majority of the participants were non‐trauma patients (N = 64; 86.5%). Therefore, the results of this review are applicable to adults with open abdomen for various abdominal diseases, especially for non‐trauma patients.

Quality of the evidence

Both studies were at high risk of bias due to the risk of performance bias and detection bias. There were too few studies included for each comparison to assess inconsistency and publication bias. There was indirectness of evidence because the studies included 10 trauma patients. The sample size was small and the confidence intervals of the majority of outcomes were wide, indicating that the estimates of effect obtained were imprecise. Overall, we considered the certainty of the evidence to be very low (Table 1; Table 2).

Potential biases in the review process

There were some unavoidable potential biases of note in the review process. First, when we contacted some of the investigators to request further information, we did not obtain a thorough reply. Thus, the missing data may introduce bias to this review. Additionally, we were unable to explore publication bias because we did not have access to the protocols for either included study (Auer 2021; Rencüzoğulları 2015).

Agreements and disagreements with other studies or reviews

We found one systematic review that evaluated various temporary abdominal closure techniques (e.g. NPWT, mesh, Bogota bag, zipper) for managing the open abdomen in non‐trauma patients (Atema 2015). The review included 74 studies describing 78 case series; however, only one of the included studies was a randomised controlled trial (Robledo 2007). Atema 2015 found that NPWT with continuous fascial traction was associated with better outcomes in terms of primary fascial closure of the abdomen, although it had a higher risk of fistulae formation. Atema 2015 did not make any recommendations because the overall certainty of the available evidence was very low. We did not include Robledo 2007 because the study compared open versus closed management of the open abdomen in people with severe peritonitis.

We found another systematic review that compared NPWT and non‐NPWT techniques for managing the open abdomen (Cirocchi 2016). The review included two randomised controlled trials (Bee 2008; Rencüzoğulları 2015); however, we excluded one of the two studies from our review (Bee 2008), as the majority of participants in the randomised controlled trial (90%) were trauma patients, and the results for non‐trauma patients were not presented separately. We included the other study in our review (Rencüzoğulları 2015). The Cirocchi 2016 review concluded that NPWT was associated with better outcomes than non‐NPWT techniques for managing the open abdomen. However, Cirocchi 2016 did not conduct a GRADE assessment. Our review includes GRADE assessments, and the findings do not agree with those of the Cirocchi 2016 review. Our review found that it is uncertain whether NPWT is better than non‐NPWT techniques (e.g. Bogota bag).

Finally, National Institute for Health and Care Excellence (NICE) guidelines reviewed the data regarding the use of NPWT for managing the open abdomen (NICE 2013). These guidelines included two randomised controlled trials (Bee 2008; Pliakos 2010); however, we excluded both studies from our review. We excluded Bee 2008 for the reasons given above. We excluded Pliakos 2010 because the primary intervention in this study was not NPWT (NPWT + retentions sutured sequential fascial closure versus NPWT). NICE guidelines concluded that the evidence on the safety and efficacy of NPWT for the open abdomen was adequate to support the use of this procedure, but they also encouraged more research on this issue. The findings from our review agreed with the NICE guidelines that further robust randomised controlled trial research would help to reduce uncertainty regarding the effectiveness and safety of NPWT for managing the open abdomen after surgery in people who have not experienced trauma.

Authors' conclusions

Implications for practice.

Based on the available trial data, we are uncertain whether negative pressure wound therapy (NPWT) has any benefit in terms of primary fascial closure of the abdomen, adverse events (fistulae formation), all‐cause mortality, or length of hospital stay compared with a Bogota bag. We are also uncertain whether the Suprasorb CNP system has any benefit in primary fascial closure of the abdomen, adverse events, all‐cause mortality, or reoperation rate compared with the ABThera system. Given the uncertainty of evidence in this review, clinicians, patients, and other stakeholders may need to take into account other considerations when making treatment decisions.

Implications for research.

Although two studies are ongoing and their results will hopefully add to the evidence regarding open abdomen (Kirkpatrick 2018; Rajabaleyan 2019), there is an urgent need for more high‐quality trials on this topic. We will update this review when data from the large ongoing studies are available.

The design of future randomised controlled trials should consider carefully ongoing trials and stakeholder priorities in this field in terms of participant populations, priority comparisons, and outcomes. Future research should report clinically important outcomes, such as primary fascial closure of the abdomen. Other outcomes to consider in conjunction with stakeholders in trial design include participant health‐related quality of life, reoperation rate, wound infection, and pain outcomes. Current practices and national or international epidemiological data that indicate the size and need of different groups may inform the choice of study population.

Trial design should be robust with use of blinded outcome assessment where possible, especially for more subjective outcomes such as primary fascial closure of the abdomen. Study sample sizes need to reflect the clinically important differences of the selected primary outcomes.

History

Protocol first published: Issue 8, 2020

Appendices

Appendix 1. Search strategies

Cochrane Wounds Specialised Register

1 MESH DESCRIPTOR Negative‐Pressure Wound Therapy EXPLODE ALL AND INREGISTER

2 MESH DESCRIPTOR Suction EXPLODE ALL AND INREGISTER

3 MESH DESCRIPTOR Vacuum EXPLODE ALL AND INREGISTER

4 ("negative pressure" or negative‐pressure or TNP or NWPT or NPWT) AND INREGISTER

5 (sub‐atmospheric or subatmospheric) AND INREGISTER

6 ((seal* next surface*) or (seal* next aspirat*)) AND INREGISTER

7 (wound near2 suction*) AND INREGISTER

8 (wound near5 drainage) AND INREGISTER

9 ((foam next suction) or (suction next dressing*)) AND INREGISTER

10 ((vacuum next therapy) or (vacuum next dressing*) or (vacuum next seal*) or (vacuum next assist*) or (vacuum near closure) or (vacuum next compression) or (vacuum next pack*) or (vacuum next drainage) or (suction near drainage) or VAC) AND INREGISTER

11 #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10 AND INREGISTER

12 MESH DESCRIPTOR Abdomen EXPLODE ALL WITH QUALIFIER SU AND INREGISTER

13 MESH DESCRIPTOR Laparotomy EXPLODE ALL AND INREGISTER

14 MESH DESCRIPTOR Abdominal Injuries EXPLODE ALL AND INREGISTER

15 MESH DESCRIPTOR Abdominal Cavity EXPLODE ALL AND INREGISTER

16 MESH DESCRIPTOR Abdominal Wall EXPLODE ALL AND INREGISTER

17 ("open abdomen" or "open abdominal" or "abdominal closure") AND INREGISTER

18 #12 OR #13 OR #14 OR #15 OR #16 OR #17 AND INREGISTER

19 #11 AND #18 AND INREGISTER

The Cochrane Central Register of Controlled Clinical Trials (CENTRAL) searched via Cochrane Register of Studies

1 MESH DESCRIPTOR Negative‐Pressure Wound Therapy EXPLODE ALL AND CENTRAL:TARGET

2 MESH DESCRIPTOR Suction EXPLODE ALL AND CENTRAL:TARGET

3 MESH DESCRIPTOR Vacuum EXPLODE ALL AND CENTRAL:TARGET

4 ("negative pressure" or negative‐pressure or TNP or NWPT or NPWT) AND CENTRAL:TARGET

5 (sub‐atmospheric or subatmospheric) AND CENTRAL:TARGET

6 ((seal* next surface*) or (seal* next aspirat*)) AND CENTRAL:TARGET

7 (wound near2 suction*) AND CENTRAL:TARGET

8 (wound near5 drainage) AND CENTRAL:TARGET

9 ((foam next suction) or (suction next dressing*)) AND CENTRAL:TARGET

10 ((vacuum next therapy) or (vacuum next dressing*) or (vacuum next seal*) or (vacuum next assist*) or (vacuum near closure) or (vacuum next compression) or (vacuum next pack*) or (vacuum next drainage) or (suction near drainage) or VAC) AND CENTRAL:TARGET

11 #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 OR #9 OR #10 AND CENTRAL:TARGET

12 MESH DESCRIPTOR Abdomen EXPLODE ALL WITH QUALIFIER SU AND CENTRAL:TARGET

13 MESH DESCRIPTOR Laparotomy EXPLODE ALL AND CENTRAL:TARGET

14 MESH DESCRIPTOR Abdominal Injuries EXPLODE ALL AND CENTRAL:TARGET

15 MESH DESCRIPTOR Abdominal Cavity EXPLODE ALL AND CENTRAL:TARGET

16 MESH DESCRIPTOR Abdominal Wall EXPLODE ALL AND CENTRAL:TARGET

17 ("open abdomen" or "open abdominal" or "abdominal closure") AND CENTRAL:TARGET

18 #12 OR #13 OR #14 OR #15 OR #16 OR #17 AND CENTRAL:TARGET

19 #11 AND #18 AND CENTRAL:TARGET

Trial registry specific search of the Cochrane Central Register of Controlled Clinical Trials (CENTRAL) searched via Cochrane Register of Studies (appended to CENTRAL search above)

20           (NCT0* or ACTRN* or ChiCTR* or DRKS* or EUCTR* or eudract* or IRCT* or ISRCTN* or JapicCTI* or JPRN* or NTR0* or NTR1* or NTR2* or NTR3* or NTR4* or NTR5* or NTR6* or NTR7* or NTR8* or NTR9* or SRCTN* or UMIN0*):AU AND CENTRAL:TARGET

21           http*:SO AND CENTRAL:TARGET

22           #20 OR #21

23           #19 AND #22

MEDLINE Ovid

1 exp Negative‐Pressure Wound Therapy/

2 exp Suction/

3 exp Vacuum/

4 (negative pressure or negative‐pressure or TNP or NPWT or NWPT).tw.

5 (sub‐atmospheric or subatmospheric).tw.

6 ((seal* adj surface*) or (seal* adj aspirat*)).tw.

7 (wound adj2 suction*).tw.

8 (wound adj5 drainage).tw.

9 ((foam adj suction) or (suction adj dressing*)).tw.

10 ((vacuum adj therapy) or (vacuum adj dressing*) or (vacuum adj seal*) or (vacuum adj closure) or (vacuum adj assist*) or (vacuum adj compression) or (vacuum adj pack*) or (vacuum adj drainage) or (suction* adj drainage) or VAC).tw.

11 or/1‐10

12 exp Abdomen/su [Surgery]

13 exp Laparotomy/

14 exp Abdominal Injuries/

15 exp Abdominal Cavity/

16 exp Abdominal Wall/

17 (open abdomen or open abdominal or abdominal closure).tw.

18 or/12‐17

19 11 and 18

20 randomized controlled trial.pt.

21 controlled clinical trial.pt.

22 randomized.ab.

23 placebo.ab.

24 drug therapy.fs.

25 randomly.ab.

26 trial.ab.

27 groups.ab.

28 or/20‐27

29 exp animals/ not humans.sh.

30 28 not 29

31 19 and 30

Embase Ovid

1 exp vacuum assisted closure/

2 exp Suction/

3 exp Vacuum/

4 (negative pressure or negative‐pressure or TNP or NWPT or NPWT).tw.

5 (sub‐atmospheric or subatmospheric).tw.

6 ((seal* adj surface*) or (seal* adj aspirat*)).tw.

7 (wound adj2 suction*).tw.

8 (wound adj5 drainage).tw.

9 ((foam adj suction) or (suction adj dressing*)).tw.

10 ((vacuum adj therapy) or (vacuum adj dressing*) or (vacuum adj seal*) or (vacuum adj closure) or (vacuum adj assist*) or (vacuum adj compression) or (vacuum adj pack*) or (vacuum adj drainage) or (suction* adj drainage) or VAC).tw.

11 or/1‐10

12 exp Abdomen/su [Surgery]

13 exp Laparotomy/

14 exp abdominal injury/

15 exp Abdominal Cavity/

16 exp abdominal wall/

17 (open abdomen or open abdominal or abdominal closure).tw.

18 or/12‐17

19 11 and 18

20 Randomized controlled trial/

21 Controlled clinical study/

22 Random$.ti,ab.

23 randomization/

24 intermethod comparison/

25 placebo.ti,ab.

26 (compare or compared or comparison).ti.

27 ((evaluated or evaluate or evaluating or assessed or assess) and (compare or compared or comparing or comparison)).ab.

28 (open adj label).ti,ab.

29 ((double or single or doubly or singly) adj (blind or blinded or blindly)).ti,ab.

30 double blind procedure/

31 parallel group$1.ti,ab.

32 (crossover or cross over).ti,ab.

33 ((assign$ or match or matched or allocation) adj5 (alternate or group$1 orintervention$1 or patient$1 or subject$1 or participant$1)).ti,ab.

34 (assigned or allocated).ti,ab.

35 (controlled adj7 (study or design or trial)).ti,ab.

36 (volunteer or volunteers).ti,ab.

37 trial.ti.

38 or/20‐37

39 (exp animal/ or animal.hw. or nonhuman/) not (exp human/ or human cell/ or (human or humans).ti.)

40 38 not 39

41 19 and 40

CINAHL EBSCO Plus

S42 S18 AND S41

S41 S40 NOT S39

S40 S19 OR S20 OR S21 OR S22 OR S23 OR S24 OR S25 OR S26 OR S27 OR S28 OR S29 OR S30 OR S31 OR S32 OR S33

S39 S37 NOT S38

S38 MH (human)

S37 S34 OR S35 OR S36

S36 TI (animal model*)

S35 MH (animal studies)

S34 MH animals+

S33 AB (cluster W3 RCT)

S32 MH (crossover design) OR MH (comparative studies)

S31 AB (control W5 group)

S30 PT (randomized controlled trial)

S29 MH (placebos)

S28 MH (sample size) AND AB (assigned OR allocated OR control)

S27 TI (trial)

S26 AB (random*)

S25 TI (randomised OR randomized)

S24 MH cluster sample

S23 MH pretest‐posttest design

S22 MH random assignment

S21 MH single‐blind studies

S20 MH double‐blind studies

S19 MH randomized controlled trials

S18 S11 AND S17

S17 S12 OR S13 OR S14 OR S15 OR S16

S16 TI ( open abdomen or open abdominal or abdominal closure ) or AB ( open abdomen or open abdominal or abdominal closure )

S15 (MH "Abdominal Muscles+")

S14 (MH "Abdominal Injuries+")

S13 (MH "Laparotomy")

S12 (MH "Abdomen+/SU")

S11 S1 OR S2 OR S3 OR S4 OR S5 OR S6 OR S7 OR S8 OR S9 OR S10

S10 TI ( vacuum therapy or vacuum dressing* or vacuum seal* or vacuum closure or vacuum compression or vacuum pack or vacuum drainage or vacuum assisted or suction drainage or VAC ) OR AB ( vacuum therapy or vacuum dressing* or vacuum seal* or vacuum closure or vacuum compression or vacuum pack or vacuum drainage or vacuum assisted or suction drainage or VAC )

S9 TI ( foam suction or suction dressing*) OR AB ( foam suction or suction dressing*)

S8 TI (wound N5 drainage) OR AB (wound N5 drainage)

S7 TI (wound N2 suction*) OR AB (wound N2 suction*)

S6 TI ( (seal* N1 surface* or seal* N1 aspirat*) ) OR AB ( (seal* N1 surface* or seal* N1 aspirat*)

S5 TI ( sub‐atmospheric or subatmospheric ) OR AB ( sub‐atmospheric or subatmospheric )

S4 TI ( negative pressure or negative‐pressure or TNP or NPWT or NWPT ) OR AB ( negative pressure or negative‐pressure or TNP or NPWT or NWPT )

S3 (MH "Vacuum")

S2 (MH "Suction+")

S1 (MH "Negative Pressure Wound Therapy")

US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov

negative pressure OR vacuum OR NPWT OR TNP OR VAC | abdomen

negative pressure OR vacuum OR NPWT OR TNP OR VAC | Laparotomy

World Health Organization International Clinical Trials Registry Platform

(negative pressure OR vacuum OR NPWT OR TNP OR VAC) AND abdomen

(negative pressure OR vacuum OR NPWT OR TNP OR VAC) AND Laparotomy

Appendix 2. Risk of bias assessment (individually randomised controlled trials)

1. Was the allocation sequence randomly generated?

Low risk of bias

The investigators describe a random component in the sequence generation process, such as referring to a random number table; using a computer random number generator; coin tossing; shuffling cards or envelopes; throwing dice; drawing of lots.

High risk of bias

The investigators describe a non‐random component in the sequence generation process. Usually, the description would involve some systematic, non‐random approach, for example, sequence generated by odd or even date of birth; sequence generated by some rule based on date (or day) of admission; sequence generated by some rule based on hospital or clinic record number.

Unclear risk of bias

Insufficient information about the sequence generation process provided to permit a judgement of low or high risk of bias.

2. Was the treatment allocation adequately concealed?

Low risk of bias

Participants and investigators enrolling participants could not foresee assignment because one of the following, or an equivalent method, was used to conceal allocation: central allocation (including telephone, web‐based, and pharmacy‐controlled randomisation); sequentially numbered drug containers of identical appearance; sequentially‐numbered, opaque, sealed envelopes.

High risk of bias

Participants or investigators enrolling participants could possibly foresee assignments and thus introduce selection bias, such as allocation based on use of an open random allocation schedule (e.g. a list of random numbers); assignment envelopes without appropriate safeguards (e.g. envelopes were unsealed, non‐opaque, or not sequentially numbered); alternation or rotation; date of birth; case record number; any other explicitly unconcealed procedure.

Unclear risk of bias

Insufficient information provided to permit a judgement of low or high risk of bias. This is usually the case if the method of concealment is not described, or not described in sufficient detail to allow a definite judgement, for example, if the use of assignment envelopes is described, but it remains unclear whether envelopes were sequentially numbered, opaque and sealed.

3. Blinding – was knowledge of the allocated interventions adequately prevented during the study?

Low risk of bias

Any one of the following.

• No blinding, but the review authors judge that the outcome and the outcome measurement are not likely to be influenced by lack of blinding.

• Blinding of participants and key study personnel ensured, and unlikely that the blinding could have been broken.

• Either participants or some key study personnel were not blinded, but outcome assessment was blinded and the non‐blinding of others unlikely to introduce bias.

High risk of bias

Any one of the following.

• No blinding or incomplete blinding, and the outcome or outcome measurement is likely to be influenced by lack of blinding.

• Blinding of key study participants and personnel attempted, but likely that the blinding could have been broken.

• Either participants or some key study personnel were not blinded, and the non‐blinding of others likely to introduce bias.

Unclear risk of bias

Either of the following.

• Insufficient information to permit judgement of low or high risk of bias.

• The study did not address this outcome.

4. Were incomplete outcome data adequately addressed?

Low risk of bias

Any one of the following.

• No missing outcome data.

• Reasons for missing outcome data are unlikely to be related to true outcome (for survival data, censoring unlikely to be introducing bias).

• Missing outcome data are balanced in numbers across intervention groups, with similar reasons for missing data across groups.

• For dichotomous outcome data, the proportion of missing outcomes compared with the observed event risk is not enough to have a clinically relevant impact on the intervention effect estimate.

• For continuous outcome data, a plausible effect size (difference in means or standardised difference in means) among missing outcomes is not enough to have a clinically relevant impact on the observed effect size.

• Missing data have been imputed using appropriate methods.

High risk of bias

Any one of the following.

• Reason for missing outcome data are likely to be related to the true outcome, with either an imbalance in numbers or reasons for missing data across intervention groups.

• For dichotomous outcome data, the proportion of missing outcomes compared with the observed event risk is enough to induce clinically relevant bias in the intervention effect estimate.

• For continuous outcome data, a plausible effect size (difference in means or standardised difference in means) among missing outcomes is enough to induce a clinically relevant bias in the observed effect size.

• 'As‐treated' analysis done with a substantial departure of the intervention received from that assigned at randomisation.

• Potentially inappropriate application of simple imputation.

Unclear risk of bias

Either of the following.

• Insufficient reporting of attrition/exclusions to permit a judgement of low or high risk of bias (e.g. number randomised not stated, no reasons for missing data provided).

• The study did not address this outcome.

5. Are reports of the study free of suggestion of selective outcome reporting?

Low risk of bias

Either of the following.

• The study protocol is available and all of the study's prespecified (primary and secondary) outcomes that are of interest in the review have been reported in the prespecified way.

• The study protocol is not available, but it is clear that the published reports include all expected outcomes, including those that were prespecified (convincing text of this nature may be uncommon).

High risk of bias

Any one of the following.

• Not all of the study's prespecified primary outcomes have been reported.

• One or more primary outcomes is/are reported using measurements, analysis methods, or subsets of the data (e.g. subscales) that were not prespecified.

• One or more reported primary outcomes was/were not prespecified (unless clear justification for their reporting is provided, such as an unexpected adverse effect).

• One or more outcomes of interest in the review is/are reported incompletely so that they cannot be entered in a meta‐analysis.

• The study report fails to include results for a key outcome that would be expected to have been reported for such a study.

Unclear risk of bias

Insufficient information provided to permit a judgement of low or high risk of bias. It is likely that the majority of studies will fall into this category.

6. Other sources of potential bias

Low risk of bias

The study appears free of other sources of bias.

High risk of bias

There is at least one important risk of bias. For example, the study:

• had a potential source of bias related to the specific study design used; or

• has been claimed to have been fraudulent; or

• had some other problem.

Unclear risk of bias

There may be a risk of bias, but there is either:

• insufficient information to assess whether an important risk of bias exists; or

• insufficient rationale or evidence that an identified problem will introduce bias.

Data and analyses

Comparison 1. NPWT versus Bogota bag.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Time to primary fascial closure of the abdomen	1	40	Mean Difference (IV, Fixed, 95% CI)	‐3.60 [‐8.16, 0.96]
1.2 Adverse events	1	40	Risk Ratio (M‐H, Fixed, 95% CI)	2.00 [0.20, 20.33]
1.3 All‐cause mortality	1	40	Risk Ratio (M‐H, Fixed, 95% CI)	0.71 [0.27, 1.88]
1.4 Length of hospital stay	1	40	Mean Difference (IV, Fixed, 95% CI)	1.10 [‐13.39, 15.59]

Comparison 2. Suprasorb CNP system versus ABThera system.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
2.1 Proportion of participants with successful primary fascial closure of the abdomen	1	34	Risk Ratio (M‐H, Fixed, 95% CI)	0.80 [0.56, 1.14]
2.2 Adverse events	1	34	Risk Ratio (M‐H, Fixed, 95% CI)	0.11 [0.01, 1.92]
2.3 All‐cause mortality	1	34	Risk Ratio (M‐H, Fixed, 95% CI)	0.33 [0.04, 2.89]
2.4 Reoperation rate	1	34	Risk Ratio (M‐H, Fixed, 95% CI)	1.00 [0.90, 1.12]

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Auer 2021.

Study characteristics
Methods	Randomised controlled trial
Participants	Country: Austria, single centre Study dates: August 2010 to September 2012 Number randomised: 34 Postrandomisation dropout: 0 (0%) Description of sample size calculation: yes Age range: 23.0 to 79.0 Mean age: 55.0 years Females: 12 (35.3%) Severe peritonitis: 31 (91.2%) Abdominal trauma: 3 (8.8%) Other etiologies: 0 (0%) Inclusion criteria People with secondary peritonitis in at least 2 abdominal quadrants People who had exhibited peritonitis for more than 24 hours and in whom a second look was planned or for whom the abdomen could not be closed for other reasons People presenting with abdominal compartment syndrome for whom the indication for open abdominal treatment after failure of conservative treatment was made People after abdominal trauma combined with abdominal compartment syndrome or contaminated abdomen due to enteral perforation, or both Exclusion criteria People with pancreatitis as the source of peritonitis People with active abdominal bleeding Pregnancy People under 18 years of age
Interventions	Participants were randomly assigned to 2 groups: Group 1: Suprasorb CNP System (N = 17) Group 2: ABThera system (N = 17)
Outcomes	The outcomes reported were: proportion of participants with successful primary fascial closure of the abdomen; adverse events (fistulae formation); all‐cause mortality; and reoperation rate.
Notes	Funding source: medical university scientific budget Declarations of interest: none declared
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Patients were randomly assigned to experimental groups using the web‐based randomizer." Comment: computer‐generated numbers
Allocation concealment (selection bias)	Low risk	Quote: "The inclusion was carried out without any influence from the treating surgeon by calling up the selection decision on the web based randomizer." Comment: central allocation
Blinding of participants and personnel (performance bias) All outcomes	High risk	Comment: the surgeons could not be blinded to group allocation.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Quote: "Even if the assessment was carried out by 2 surgeons on the basis of photos presented, the study could not be blinded."
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: there were no postrandomisation dropouts.
Selective reporting (reporting bias)	Low risk	Comment: the study protocol was not available; the study included results for expected key outcomes.
Other bias	High risk	Quote: "The values of BMI are displayed in Table 1E. The difference between the groups was significant." Comment: baseline imbalance

Rencüzoğulları 2015.

Study characteristics
Methods	Randomised controlled trial
Participants	Country: Turkey, single centre Study dates: not reported Number randomised: 40 Postrandomisation dropout: 0 (0%) Description of sample size calculation: no Age range: 24.0 to 81.0 Mean age: 50.9 years Females: 17 (42.5%) Severe peritonitis: 24 (60%) Abdominal trauma: 7 (17.5%) Other etiologies: 9 (22.5%) Inclusion criteria People undergoing decompressive laparotomy as part of the treatment for abdominal compartment syndrome People who were under follow‐up in the surgical intensive care unit People who developed abdominal compartment syndrome as a result of progressively increasing intra‐abdominal pressure Exclusion criteria People with American Society of Anesthesologists score 5
Interventions	Participants were randomly assigned to 2 groups: Group 1: vacuum‐assisted closure (N = 20) Group 2: Bogota bag (N = 20)
Outcomes	The outcomes reported were: primary fascial closure of the abdomen; adverse events (fistulae formation); all‐cause mortality; length of hospital stay; and intra‐abdominal pressure.
Notes	Vacuum‐assisted closure system (V.A.C., KCI, San Antonio, TX) was applied to temporary abdominal closure. Funding source: not reported Declarations of interest: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Comment: the paper did not provide any information about sequence generation.
Allocation concealment (selection bias)	Unclear risk	Comment: the paper did not provide any information about allocation concealment.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Author reply: "We cannot define as blinded, as [the] surgical and postoperative care team were aware of randomization."
Blinding of outcome assessment (detection bias) All outcomes	High risk	Author reply: "We cannot define as blinded, as [the] surgical and postoperative care team were aware of randomization."
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: there were no postrandomisation dropouts.
Selective reporting (reporting bias)	Low risk	Comment: the study protocol was not available; the study included results for expected key outcomes.
Other bias	Low risk	Comment: the study appeared to be free of other sources of bias.

Characteristics of excluded studies [ordered by study ID]

Study	Reason for exclusion
Barker 2000	This was a non‐randomised study.
Bee 2008	The majority of participants in this randomised controlled trial (90%) were trauma patients, and the results for non‐trauma patients were not presented separately.
Correa 2016	A total of 52% of the participants in this randomised controlled trial were trauma patients, and the results for non‐trauma patients were not presented separately.
Fortelny 2014	This was a non‐randomised study.
Kirkpatrick 2015	A total of 46% of the participants in this randomised controlled trial were trauma patients, and the results for non‐trauma patients were not presented separately.
Kurt 2021	This was a non‐randomised study.
Long 2014	A total of 35% of the participants in this randomised controlled trial were trauma patients, and the results for non‐trauma patients were not presented separately.
Perathoner 2010	This was a non‐randomised study.
Pliakos 2010	This was a randomised controlled trial comparing negative pressure wound therapy (NPWT) + retentions sutured sequential fascial closure versus NPWT. Thus, the primary intervention was retentions sutured sequential fascial closure rather than NPWT.
Villalobos 2020	This was a non‐randomised study.

Characteristics of ongoing studies [ordered by study ID]

Kirkpatrick 2018.

Study name	Closed or open after source control laparotomy for severe complicated intra‐abdominal sepsis (the COOL trial): study protocol for a randomised controlled trial
Methods	Randomised controlled trial
Participants	Country: Canada Number at enrolment: 550 Inclusion criteria Presence of purulent, feculent, or enteric spillage over at least 2 intraperitoneal quadrants intraoperatively Septic shock Predisposition, Infection, Response and Organ Dysfunction score > 3 World Society of Emergency Surgery Sepsis Severity score > 8 Exclusion criteria Pregnant Confirmed or strongly suspected severe intra‐abdominal hypertension (intra‐abdominal pressure > 20 mmHg) No intention of providing ongoing care Pancreatitis as the source of peritonitis Uncontrolled bleeding
Interventions	Participants were randomly assigned to 2 groups: Group 1: negative pressure wound therapy management Group 2: closed abdomen management
Outcomes	The primary outcome is the rate of survival of participants. The secondary outcomes are the length of days in intensive care unit and the concentrations of blood interleukin‐6.
Starting date	May 2017
Contact information	Principal investigator: Andrew W Kirkpatrick, University of Calgary, Canada Email: Andrew.kirkpatrick@albertahealthservices.ca
Notes

Rajabaleyan 2019.

Study name	Vacuum assisted closure versus on‐demand re‐laparotomy in patients with faecal or diffuse peritonitis: a multicenter randomised controlled trial (VACOR)
Methods	Randomised controlled trial
Participants	Country: Denmark Number at enrolment: 320 Inclusion criteria Age over 18 Suspected faecal peritonitis originating from the small intestine, colon, or rectum Exclusion criteria Primary peritonitis Abdominal trauma Lack of consent
Interventions	Participants were randomly assigned to 2 groups: Group 1: negative pressure wound therapy management Group 2: closed abdomen management
Outcomes	The primary outcome is peritonitis‐related complications. The secondary outcomes are quality of life, ventral hernia rate, and cost‐effective analysis.
Starting date	April 2019
Contact information	Principal investigator: Pooya Rajabaleyan, Odense University Hospital, Denmark Email: Pooya.Rajabaleyan@rsyd.dk
Notes

Differences between protocol and review

• We updated our search terms by adding intervention terms that retrieved additional relevant results.

• We did not perform any subgroup analyses because there was an insufficient number of studies included in the review.

• We did not perform funnel plots to assess reporting biases because there were fewer than 10 included studies.

• We added size of the wound to Data extraction and management.

Contributions of authors

Yao Cheng: designed the review; undertook quality assessment; produced the first draft of the review; performed previous work that was the foundation of the current review; approved final review prior to submission; is guarantor of the review.

Ke Wang: co‐ordinated the review; selected which trials to include; produced the first draft of the review; approved final review prior to submission.

Junhua Gong: selected which trials to include; extracted data; analysed or interpreted data; performed statistical analysis; contributed to writing or editing the review; approved final review prior to submission.

Zuojin Liu: conceived the review; extracted data; contributed to writing or editing the review; advised on the review; approved final review prior to submission.

Jianping Gong: analysed or interpreted data; performed statistical analysis; contributed to writing or editing the review; advised on the review; approved final review prior to submission.

Zhong Zeng: undertook quality assessment; contributed to writing or editing the review; secured funding; approved final review prior to submission.

Xiaomei Wang: checked quality of data extraction; checked quality assessment; checked quality of statistical analysis; contributed to writing or editing the review; wrote to study authors, experts, and companies; approved final review prior to submission.

Contributions of editorial base

Gill Norman (Editor): edited the protocol; advised on methodology, interpretation, and content; approved the final protocol prior to publication.

Jo Dumville (Joint Co‐ordinating Editor): advised on methodology, interpretation, and content; approved the final review prior to publication.

Gill Rizzello (Managing Editor): co‐ordinated the editorial process; advised on interpretation and content; edited the review.

Sophie Bishop (Information Specialist): designed the search strategy; ran the search; and edited the search methods section.

Tom Patterson (Editorial Assistant): wrote the plain language summary and checked the reference sections.

Sources of support

Internal sources

• Chongqing Medical University, Other

  This review was supported by the National Natural Science Foundation of China (Grant Nos. 81701950, 82172135), Medical Research Projects of Chongqing (Grant Nos. 2018MSXM132, 2020FYYZ248), and the Kuanren Talents Program of the second affiliated hospital of Chongqing Medical University (Grant No. KY2019Y002).

External sources

• The National Institute for Health Research (NIHR), UK

  This project was supported by the National Institute for Health Research, via Cochrane Infrastructure funding to Cochrane Wounds. The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care.

Declarations of interest

Yao Cheng: has declared that they have no conflict of interest.
Ke Wang: has declared that they have no conflict of interest.
Junhua Gong: has declared that they have no conflict of interest.
Zuojin Liu: has declared that they have no conflict of interest.
Jianping Gong: works as a healthcare professional.
Zhong Zeng: works as a healthcare professional.
Xiaomei Wang: works as a healthcare professional.

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