Intracavity lavage and wound irrigation for prevention of surgical site infection

Gill Norman; Ross A Atkinson; Tanya A Smith; Ceri Rowlands; Amber D Rithalia; Emma J Crosbie; Jo C Dumville

doi:10.1002/14651858.CD012234.pub2

. 2017 Oct 30;2017(10):CD012234. doi: 10.1002/14651858.CD012234.pub2

Intracavity lavage and wound irrigation for prevention of surgical site infection

Gill Norman ^1,^✉, Ross A Atkinson ¹, Tanya A Smith ², Ceri Rowlands ³, Amber D Rithalia ⁴, Emma J Crosbie ⁵, Jo C Dumville ¹

Editor: Cochrane Wounds Group

PMCID: PMC5686649 PMID: 29083473

Abstract

Background

Surgical site infections (SSIs) are wound infections that occur after an operative procedure. A preventable complication, they are costly and associated with poorer patient outcomes, increased mortality, morbidity and reoperation rates. Surgical wound irrigation is an intraoperative technique, which may reduce the rate of SSIs through removal of dead or damaged tissue, metabolic waste, and wound exudate. Irrigation can be undertaken prior to wound closure or postoperatively. Intracavity lavage is a similar technique used in operations that expose a bodily cavity; such as procedures on the abdominal cavity and during joint replacement surgery.

Objectives

To assess the effects of wound irrigation and intracavity lavage on the prevention of surgical site infection (SSI).

Search methods

In February 2017 we searched the Cochrane Wounds Specialised Register; the Cochrane Central Register of Controlled Trials (CENTRAL); Ovid MEDLINE; Ovid Embase and EBSCO CINAHL Plus. We also searched three clinical trials registries and references of included studies and relevant systematic reviews. There were no restrictions on language, date of publication or study setting.

Selection criteria

We included all randomised controlled trials (RCTs) of participants undergoing surgical procedures in which the use of a particular type of intraoperative washout (irrigation or lavage) was the only systematic difference between groups, and in which wounds underwent primary closure. The primary outcomes were SSI and wound dehiscence. Secondary outcomes were mortality, use of systemic antibiotics, antibiotic resistance, adverse events, re‐intervention, length of hospital stay, and readmissions.

Data collection and analysis

Two review authors independently assessed studies for inclusion at each stage. Two review authors also undertook data extraction, assessment of risk of bias and GRADE assessment. We calculated risk ratios or differences in means with 95% confidence intervals where possible.

Main results

We included 59 RCTs with 14,738 participants. Studies assessed comparisons between irrigation and no irrigation, between antibacterial and non‐antibacterial irrigation, between different antibiotics, different antiseptics or different non‐antibacterial agents, or between different methods of irrigation delivery. No studies compared antiseptic with antibiotic irrigation.

Surgical site infection

Irrigation compared with no irrigation (20 studies; 7192 participants): there is no clear difference in risk of SSI between irrigation and no irrigation (RR 0.87, 95% CI 0.68 to 1.11; I² = 28%; 14 studies, 6106 participants). This would represent an absolute difference of 13 fewer SSIs per 1000 people treated with irrigation compared with no irrigation; the 95% CI spanned from 31 fewer to 10 more SSIs. This was low‐certainty evidence downgraded for risk of bias and imprecision.

Antibacterial irrigation compared with non‐antibacterial irrigation (36 studies, 6163 participants): there may be a lower incidence of SSI in participants treated with antibacterial irrigation compared with non‐antibacterial irrigation (RR 0.57, 95% CI 0.44 to 0.75; I² = 53%; 30 studies, 5141 participants). This would represent an absolute difference of 60 fewer SSIs per 1000 people treated with antibacterial irrigation than with non‐antibacterial (95% CI 35 fewer to 78 fewer). This was low‐certainty evidence downgraded for risk of bias and suspected publication bias.

Comparison of irrigation of two agents of the same class (10 studies; 2118 participants): there may be a higher incidence of SSI in participants treated with povidone iodine compared with superoxidised water (Dermacyn) (RR 2.80, 95% CI 1.05 to 7.47; low‐certainty evidence from one study, 190 participants). This would represent an absolute difference of 95 more SSIs per 1000 people treated with povidone iodine than with superoxidised water (95% CI 3 more to 341 more). All other comparisons found low‐ or very low‐certainty evidence of no clear difference between groups.

Comparison of two irrigation techniques: two studies compared standard (non‐pulsed) methods with pulsatile methods. There may, on average, be fewer SSIs in participants treated with pulsatile methods compared with standard methods (RR 0.34, 95% CI 0.19 to 0.62; I² = 0%; two studies, 484 participants). This would represent an absolute difference of 109 fewer SSIs occurring per 1000 with pulsatile irrigation compared with standard (95% CI 62 fewer to 134 fewer). This was low‐certainty evidence downgraded twice for risks of bias across multiple domains.

Wound dehiscence

Few studies reported wound dehiscence. No comparison had evidence for a difference between intervention groups. This included comparisons between irrigation and no irrigation (one study, low‐certainty evidence); antibacterial and non‐antibacterial irrigation (three studies, very low‐certainty evidence) and pulsatile and standard irrigation (one study, low‐certainty evidence).

Secondary outcomes

Few studies reported outcomes such as use of systemic antibiotics and antibiotic resistance and they were poorly and incompletely reported. There was limited reporting of mortality; this may have been partially due to failure to specify zero events in participants at low risk of death. Adverse event reporting was variable and often limited to individual event types. The evidence for the impact of interventions on length of hospital stay was low or moderate certainty; where differences were seen they were too small to be clinically important.

Authors' conclusions

The evidence base for intracavity lavage and wound irrigation is generally of low certainty. Therefore where we identified a possible difference in the incidence of SSI (in comparisons of antibacterial and non‐antibacterial interventions, and pulsatile versus standard methods) these should be considered in the context of uncertainty, particularly given the possibility of publication bias for the comparison of antibacterial and non‐antibacterial interventions. Clinicians should also consider whether the evidence is relevant to the surgical populations under consideration, the varying reporting of other prophylactic antibiotics, and concerns about antibiotic resistance.

We did not identify any trials that compared an antibiotic with an antiseptic. This gap in the direct evidence base may merit further investigation, potentially using network meta‐analysis; to inform the direction of new primary research. Any new trial should be adequately powered to detect a difference in SSIs in eligible participants, should use robust research methodology to reduce the risks of bias and internationally recognised criteria for diagnosis of SSI, and should have adequate duration and follow‐up.

Plain language summary

'Washout' during surgery for prevention of surgical site infection

What is the aim of this review?

The aim of this review was to find out whether intracavity lavage and wound irrigation (washing out a wound during surgery) can help to prevent surgical site infection (SSI). Researchers from Cochrane collected and analysed all relevant studies (randomised controlled trials) to answer this question and found 59 relevant studies.

Key messages

The certainty of all the evidence we gathered on the effect of washing out wounds on SSIs was low or very low. This was due to problems with how results were reported, some small sample sizes and concern that not all relevant evidence was published. This means that the true effects of treatments may be substantially different from our results. Washing out surgical wounds may make no clear difference to SSI rates compared with not washing out. Using antibacterial solutions to wash out wounds may reduce infection rates compared with non‐antibacterial products. Pumping the washing solution into the wound may reduce infections compared with other methods of washing out. Side effects were not well reported.

What was studied in the review?

Infections can often develop in wounds following surgery. This can prevent the wound from healing and can lead to infection spreading through the body. People with SSIs spend longer in hospital and are more likely to need a repeat operation. Techniques used to reduce the risk of infection include intracavity lavage or wound irrigation (washing out the wound during surgery using water or medicated solutions). We wanted to find out if this reduced SSI rates, and improved wound healing. We also wanted to find out about serious consequences such as severe infections that cannot be treated with antibiotics, abscesses, and lengthy hospital stays.

What are the main results of the review?

We found 59 studies involving 14,738 participants (both adults and children). Some studies enrolled only women because of the type of surgery (e.g. caesarean sections). The studies compared washing out wounds with no treatment, antibacterial and non‐antibacterial washing solutions, and different methods of washing. Follow‐up times ranged from a few days to several months but most were between two and eight weeks. Most studies did not state how they were funded, but when funding was reported it was mostly non‐commercial.

Twenty studies involving 7192 participants compared washing out with no washing. The results showed no clear difference in SSI rates (low‐certainty evidence). Antibacterial washing solutions may reduce infection rates compared with non‐antibacterial solutions (low‐certainty evidence from 36 trials involving 6163 participants). Two studies involving 484 participants compared standard washing methods (pouring using a jug or a syringe) with pumping or pulsing the washing solution. There may be fewer SSIs when the solution is pumped into the wound (low‐certainty evidence). There may be fewer SSIs when a solution of povidone iodine is used compared with an alternative antiseptic (superoxidised water, Dermacyn) (low‐certainty evidence from 1 trial with 190 participants). The results for all other comparisons showed no clear differences or were very uncertain. Wound reopening (dehiscence), infections, which are hard to treat with antibiotics, and deaths were not widely reported. Washing out wounds may not affect the length of time people stay in hospital (low‐ or moderate‐certainty evidence).

How up to date is this review?

We searched for studies that had been published up to February 2017.

Summary of findings

Background

Description of the condition

Surgical site infections (SSIs) encompass a range of superficial to deep wound infections that can occur after an operative procedure. SSIs are a preventable complication, responsible for substantial financial burden to health services that can result in poorer patient outcomes, increased mortality, morbidity and reoperation rates. A 2006 prevalence survey in the UK National Health Service (NHS) indicated that approximately 8% of all patients (5743/75,694 patients over a four‐month period) admitted to hospital suffer healthcare‐associated infections, with 15% of these infections being SSIs (Smyth 2008). A US study found that in over 750,000 episodes of surgical hospitalisation, 1% resulted in a SSI, and similar estimates have been found in France (Astagneau 2009; De Lissovoy 2009). However, such values are known to underestimate the levels of SSI by not considering those that develop outside hospitals (Bruce 2001; Gibbons 2011), as most SSIs present within the first 30 days following a procedure, although commonly between the fifth and tenth postoperative day (NICE 2008). Patients who develop SSIs have longer hospital stays and incur higher treatment costs than other patients; in some types of surgery they also have higher mortality rates (Coello 2005; Jenks 2014). Diagnosis with a SSI after hospital discharge is associated with a greater number of healthcare visits, higher resource use, and more readmissions (Perencevich 2003). While more data are available for Western healthcare settings, SSI was the leading cause of hospital‐acquired infection in a systematic review of studies in low‐ and middle‐income countries (Allegranzi 2010). Surgical site infection can also contribute to wound dehiscence, which is also a primary outcome of this review; such wounds may then convert to healing by secondary intention with a resultant increased healing time and impact on the individual and on costs to the health service.

While the cause of SSIs is multifactorial, recognised risk factors include: length of hospital stay, obesity, patient co morbidities, duration and complexity of surgery, and degree of wound contamination (Anderson 2008; Chemaly 2010; Edwards 2008; Korol 2013; Omran 2007). Using the classification system adopted by the Centers for Disease Control and Prevention (CDC; HICPAC 1999), wounds can be classified by their level of contamination as follows.

Clean (Class 1): noninfective operative wounds in which no inflammation is encountered, with no involvement of respiratory, gastrointestinal, genitourinary tract, and oropharyngeal cavity.

Clean‐contaminated (Class 2): operative wounds in which either the respiratory, gastrointestinal, or genitourinary tract is entered under controlled conditions and with only minor contamination. This category specifically includes wounds as a result of operations involving the biliary tract, appendix, and oropharynx, provided no evidence of infection or a major break in sterile technique is encountered.

Contaminated (Class 3): fresh, accidental wounds, resulting from operations with major breaks in sterile technique or gross spillage from the gastrointestinal tract, and incisions in which acute, nonpurulent (free from pus) inflammation is encountered. This category includes traumatic lacerations.

Dirty (Class 4): old traumatic wounds with retained devitalised tissue and those that involve existing clinical infection or perforated viscera. Organisms causing postoperative infection are likely to be present in the operative field before the operation.

The risk of developing a SSI is related to the level of contamination of the wound. Higher classifications of contamination are associated with higher risks of a SSI, as demonstrated in recent surveillance of surgical infections in NHS hospitals in England, which showed that gastrointestinal procedures, especially large bowel surgery, carry the highest risk of bacterial contamination (10.2%) (Public Health England 2014). Conversely, hip and knee prosthesis surgeries were shown to carry the lowest risk of infection, with an occurrence rate of 0.7% and 0.6%, respectively (Public Health England 2014).

Standard definitions of SSIs exist, as described by the CDC, the Surgical Site Infection Surveillance Service, the Southampton wound scoring system, and the ASEPSIS score (Bailey 1992; Horan 1992; Ridgeway 2005; Wilson 1986). The most commonly applied definition by the CDC describes three levels of SSI (Horan 1992). The lowest level of SSI can be defined as 'superficial incisional' infections. These are limited to the skin and subcutaneous tissue. Such infections are identified by localised clinical (Celsian) signs such as redness, pain, heat, swelling, or the drainage of pus. 'Deep incisional' infections affect the fascial and muscular layers and are identified by the presence of pus, abscess, fever, localised tenderness, or the separation of incision edges. Finally, 'cavity space' infection is considered the most severe level of SSI. Such infections can be identified by the drainage of pus, formation of an abscess or histological, radiological, or visual signs during reoperation. These involve anatomical parts of the body that have been manipulated during a surgical procedure, for example, a joint cavity or the peritoneum. Visceral infection is not included within the scope of the CDC guidelines.

SSIs are not restricted to these definitions and are often accompanied by microbiological evidence from microscopy and culture of infection tissue and fluid. However, it is important to note that normal flora may colonise superficial skin sites, and therefore positive microbiological growth in the absence of clinical signs is rarely indicative of SSIs.

Description of the intervention

Surgical wound irrigation is an intraoperative surgical technique, which may reduce the rate of SSIs by the removal of debris (dead or damaged tissue), metabolic waste, and wound exudate. It aims to create the optimal environment for wound healing, and is used with variable uptake among surgical practitioners (Barnes 2014). The theoretical advantage of surgical wound irrigation is to reduce the bacterial load in a surgical or traumatic wound by a combination of water pressure, dilution, or the application of antimicrobial agents. Usually, irrigation is undertaken at the end of an operative procedure, prior to wound closure, however postoperative wound irrigation may also be applied.

Intracavity lavage is another intraoperative surgical technique, which utilises similar principles to surgical wound irrigation with the aim of reducing SSI risk. It can be adopted during any operation that exposes a bodily cavity, but is most commonly used for procedures on the abdominal (peritoneal) cavity and during joint replacement surgery. Both wound irrigation and intracavity lavage can be altered by three basic variables: volume of irrigation fluid; mechanism/timing of delivery; or solution composition. We use the terms 'irrigation' and 'lavage' separately in this review, however they do not necessarily describe distinctly separate surgical techniques, and may often refer to similar methods of washout for a cavity or a wound.

How the intervention might work

The aim of wound irrigation and lavage is to reduce the bacterial load in a surgical or traumatic wound by a combination of water pressure, dilution, or the application of antimicrobial agents. Usually, this is undertaken at the end of an operative procedure, prior to wound closure, to reduce the likelihood of the introduction of bacteria.

Both wound irrigation and intracavity lavage can be achieved using various solutions. Normal saline is commonly used along with antimicrobial agents for intracavity lavage. However, there is concern that antimicrobial agents may damage tissue and prevent normal healing. It is thought that the introduction of large volumes of fluid into a cavity or wound could wash away inflammatory cells vital to the host defence (Schultz 2011).

Why it is important to do this review

National Institute for Care and Health Excellence (NICE) guidelines reviewed evidence from 20 randomised controlled trials (RCTs) and concluded that the use of surgical wound irrigation or intracavity lavage could not be recommended to reduce the risk of SSIs (NICE 2008). The search used to inform this guideline is now almost 10 years old, making it likely that a number of additional trials will be available. In some areas of surgical practice this is likely to lead to changes in conclusions; we are aware of a recent systematic review which found a benefit to intraoperative irrigation over no irrigation in abdominal surgery (Mueller 2015); this included both RCTs and studies that we consider to be quasi‐RCTs. A recent review restricted to prophylactic wound irrigation (excluding surgeries with high levels of contamination) has just been published (De Jonge 2017), which informed recent WHO guidance (WHO 2016) A recent expert consensus paper also identified the need for more evidence on several of the questions in this review (Barnes 2014). This review aims to update this evidence base.

Objectives

To assess the effects of wound irrigation and intracavity lavage on the prevention of surgical site infection (SSI).

Methods

Criteria for considering studies for this review

Types of studies

We included published and unpublished randomised controlled trials (RCTs), including cluster‐RCTs, irrespective of language of report. We excluded studies using quasi‐randomisation (i.e. a method of allocating participants to different forms of care that is not truly random, for example, allocation by date of birth, day of the week, medical record number, month of the year, or the order in which participants are included in the study (alternation)).

Types of participants

All patients undergoing elective or emergency surgery, where surgery was defined as a procedure involving: (1) an incision being made into the skin forming an open wound; or (2) an operative procedure to treat an existing traumatic wound/injury. We included studies including either, or both, adults and children. Only studies focusing on wounds intended to heal by primary intention (i.e. where wound edges are held together after surgery) were included in this review. This included interventions for open fractures or operated traumatic wounds if the aim of the procedure was to heal the wound by primary intention. We excluded surgery intended to create wounds with planned healing by secondary intention (i.e. left open to heal through the formation of new tissues) or wounds healing by delayed primary/tertiary intention (wounds which are intentionally initially left open for a period of time, but then have the edges brought together for the rest of the healing process).

Types of interventions

We included studies where the type or schedule of intraoperative washout (either wound irrigation or intracavity lavage) was the only systematic difference between study arms.

Surgical wound irrigation may occur as a singular event during wound closure, or involve the irrigation of a wound continuously/repeatedly during surgery, or in the postoperative period. Types of surgical wound irrigation may vary by volume of irrigation fluid, mechanism of delivery, or solution composition. We did not include studies where the irrigation was confined solely to the interior of internal organs (e.g.) the uterus, bowel or bladder, but did include studies in which (e.g.) the peritoneum was irrigated in addition to such procedures. We did not include studies of surgery in the oral or aural cavities or in the eyes.

Intracavity lavage may also occur as a singular event during surgery, which exposes a body cavity, or involve the irrigation of a cavity continuously/repeatedly during surgery, or in the postoperative period. Types of intracavity lavage again may vary by volume of irrigation fluid, mechanism of delivery, or solution composition.

In practice we found that the terms 'irrigation' and 'lavage' are often used interchangeably. We included all studies in which a washout procedure was conducted and we have used the term 'irrigation' throughout the review. Where the term 'lavage' was used in the included studies, this is reflected in the Characteristics of included studies tables; this section also details all available information on the point(s) at which irrigation occurred during surgery. We did not pre‐specify any subgrouping based on the use of irrigation or lavage or the level at which it was conducted; we have not conducted any post‐hoc analysis based on this but have followed the protocol and grouped all forms of intraoperative washout. The only exception was where one study used procedures which were so different from the other studies in the comparison that we treated this separately.

We anticipated that likely comparisons in this review may include:

comparison of wound irrigation/intracavity lavage with no washout;
comparison of different solutions used for wound irrigation or intracavity lavage;
comparison of different volumes of fluid used for wound irrigation or intracavity lavage;
comparison of different mechanisms of delivery used for wound irrigation or intracavity lavage; and
comparison of different schedules/timings of wound irrigation or intracavity lavage.

Types of outcome measures

We list primary and secondary outcome measures below. If a trial was otherwise eligible (correct study design, population, and intervention/comparator) but did not report a listed outcome, then we attempted to contact the study authors, in order to establish whether a relevant outcome was measured but not reported. However, we did not plan to exclude otherwise eligible studies solely on the basis of reported outcomes. In several instances author contact was not immediately successful and we recorded these studies as Studies awaiting classification.

Where possible, we anticipated grouping outcomes by the following time points; the review authors used their judgement as to whether statistical pooling within these time categories was appropriate:

short‐term: 30 days
medium‐term: more than 30 days to 12 months
long‐term: more than 12 months.

In practice we found that the overwhelming majority of the data reported were for time points of between two and eight weeks postoperatively, with the majority being at either four or six weeks, sometimes with interim but unreported follow‐up points. We therefore decided that we would group all the data together for the outcomes reported; we did not consider dividing data reported at points that narrowly spanned 30 days to be informative.

Primary outcomes

Surgical site infection measured as: occurrence of postoperative surgical site infection (SSI) as defined by the CDC criteria (Horan 2008), or the study authors' definition of SSI. We did not differentiate between superficial and deep incisional infection. We planned to document septicaemia or septic shock under this outcome.
Wound dehiscence within 30 days of operation. This included both superficial dehiscence (involving skin and subcutaneous tissues) or deep dehiscence (burst abdomen or dehiscence of fascia). Postoperative wound dehiscence refers to wound disruption resulting from poor wound healing. This may be caused by various factors, including infection, as well as the type of incision and patient characteristics, such as diabetes or smoking (Sandy‐Hodgetts 2015).

Secondary outcomes

30‐day mortality/in‐hospital mortality
Proportion of participants with postoperative SSI using systemic antibiotics within 30 days of surgery
Occurrence of infections that show antibiotic resistance
Adverse events including postoperative abscess formation; we planned to include these, where reported, as total number of individuals with an adverse event in each intervention group
Surgical re‐intervention rates (including the placement of radiologically‐guided drains and joint revision surgery)
Mean length of hospital stay
Number of hospital readmissions.

Search methods for identification of studies

Electronic searches

We searched the following electronic databases for randomised controlled trials:

the Cochrane Wounds Specialised Register (searched 1 February 2017);
the Cochrane Central Register of Controlled Trials (CENTRAL; 2017, issue 1) in the Cochrane Library (searched 1 February 2017);
Ovid MEDLINE (1946 to 1 February 2017);
Ovid MEDLINE (In‐Process & Other Non‐Indexed Citations) (searched 1 February 2017);
Ovid Embase (1974 to 1 February 2017);
EBSCO CINAHL Plus (1937 to 1 February 2017).

The search strategies for the Cochrane Wounds Specialised Register, CENTRAL, Ovid MEDLINE, Ovid Embase and EBSCO CINAHL Plus are available in Appendix 1. We combined the Ovid MEDLINE search with the Cochrane Highly Sensitive Search Strategy for identifying randomised trials in MEDLINE: sensitivity‐ and precision‐maximising version (2008 revision) (Lefebvre 2011). We combined the Embase search with the Ovid Embase randomised trials filter terms developed by the UK Cochrane Centre (Lefebvre 2011). We combined the CINAHL Plus searches with the randomised trials filter terms developed by the Scottish Intercollegiate Guidelines Network (SIGN 2017). We did not impose any restrictions with respect to language, date of publication, or study setting.

We also searched the following clinical trials registries for ongoing studies in March 2017:

ClinicalTrials.gov (searched 7 March 2017);
World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (searched 7 March 2017);
EU Clinical Trials Register (searched 7 March 2017).

Search strategies for the clinical trials registries are available in Appendix 1.

Searching other resources

We sought to identify 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.

Data collection and analysis

Selection of studies

Two review authors (CR and either TS or GN) 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 considered to be potentially relevant. Two review authors (GN and either CR or TS) independently checked the full papers for eligibility; disagreements were resolved by discussion and, where required, the input of a third review author (CR, TS, JD or RA as appropriate). 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, where it was not immediately obvious that the study was ineligible after being ordered due to a very sparse citation record. We completed a PRISMA flowchart to summarise this process (Liberati 2009); Figure 1.

Where studies were reported in multiple publications/reports, we obtained all publications. Whilst we included the study only once in the review, we extracted data from all reports to ensure maximal relevant data were obtained. Where it was unclear whether publications referred to the same study we attempted to contact the authors for clarification.

Data extraction and management

We extracted and summarised details of the eligible studies using a data extraction sheet. Two review authors (two of CR,TS, GN, RA and AR) extracted data independently and resolved disagreements by discussion, drawing on a third review author (JD) where required. Where key data were missing from reports, we attempted to contact the study authors to obtain this information. Where a study with more than two intervention arms was included, we only extracted data from intervention and control groups that met the eligibility criteria.

We extracted the following data, where possible, by treatment group for the prespecified interventions and outcomes in this review. We planned to collect outcome data for relevant time points, as described in Types of outcome measures; in practice most studies reported only one time point.

Country of origin
Type of wound and surgery
Unit of randomisation (e.g. participant or wound)
Unit of analysis (e.g. participant or wound)
Trial design (e.g. parallel; cluster)
Number of participants/wounds randomised to each trial arm
Eligibility criteria and key baseline participant data
Details of treatment regimen received by each group
Duration of treatment
Details of any co‐interventions
Primary and secondary outcome(s) (with definitions and time points)
Outcome data for primary and secondary outcomes (by group)
Duration of follow‐up.
Number of withdrawals (by group)
Publication status of study
Source of funding for trial.

Assessment of risk of bias in included studies

Two review authors (two of CR, TS, GN, RA or AR) independently assessed included studies using the Cochrane approach for assessing risk of bias as detailed in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011a). We resolved disagreements through discussion or by consulting a third review author (typically JD). The tool addresses specific domains: sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessors, incomplete data, selective outcome reporting, and other issues – in this review we planned to record 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). We recorded issues with adjustment for paired data in split‐body designs and with early stopping in this domain. We assessed blinding and completeness of outcome data for each of the review outcomes separately. In this review we anticipated that blinding of participants and personnel may not be possible. For this reason the assessment of the risk of detection bias focused on whether blinded outcome assessment was reported (because assessment of wound outcomes, such as breakdown and healing, can be subjective and at high risk of detection bias when outcome assessment is not blinded). We used blinding of outcome assessment to determine risk of bias from blinding in these instances. Although we recorded risk of bias from blinding of personnel and participants, we did not downgrade the certainty of the evidence for this alone, where the nature of the comparison made it highly likely. We presented our assessment of risk of bias using two 'Risk of bias' summary figures; one that is a summary of bias for each item across all studies, and a second that shows a cross‐tabulation of each trial by all of the risk of bias items (Figure 2; Figure 3).

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

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

For trials using cluster‐randomisation, we also planned to consider the risk of bias considering: recruitment bias, baseline imbalance, loss of clusters, incorrect analysis, and comparability with individually randomised trials (Higgins 2011b; Appendix 3).

Measures of treatment effect

For dichotomous outcomes, we calculated the risk ratio (RR) with 95% confidence intervals (CIs). For continuous outcomes we used the difference in means with 95% CIs, if all trials used the same or similar assessment scale. If trials had used different assessment scales, we planned to use the standardised difference in means with 95% CIs.

Unit of analysis issues

If included studies had randomised at the participant level and measured outcomes at the wound level, we planned to treat the participant as the unit of analysis when the number of wounds assessed appeared equal to the number of participants (e.g. one wound per person).

Particular unit of analysis issues in wound care trials can occur when: (1) studies randomise at the participant level, use the allocated treatment on multiple wounds per participant, and then analyse outcomes per wound; or (2) studies undertake multiple assessments of an outcome over time per participant. These approaches should be treated as cluster trials, alongside more standard cluster designs – such as delivery of interventions at an organisational level.

Where a cluster trial had been conducted and correctly analysed we planned to meta‐analyse effect estimates and their standard errors using the generic inverse‐variance method in Review Manager 5 (RevMan 2014).

We planned to record where a cluster‐randomised trial had been conducted, but incorrectly analysed as part of the 'Risk of bias' assessment. If possible, we planned to approximate the correct analyses based on guidance from the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011b), using information on:

the number of clusters (or groups) randomised to each intervention group; or the average (mean) size of each cluster;
the outcome data ignoring the cluster design for the total number of individuals (for example, number or proportion of individuals with events, or means and standard deviations); and
an estimate of the intra cluster (or intra class) correlation coefficient (ICC).

If we had been unable to analyse the study data correctly, we planned to extract and present outcome data but not analyse it further.

We did not identify any cluster randomised studies, but did identify a split‐body design in which two incisions on each participant were randomised to different treatment groups. This represented paired data and it was unclear that this had been adjusted for. Unadjusted paired data will generate confidence intervals wider than the true ones for the effect estimate. We presented the results of the single study with this design in narrative form, but did not include data from the study in any meta‐analysis.

Dealing with missing data

It is common to have data missing from trial reports. Excluding participants post‐randomisation 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 thought should be included in the analyses, or where data were unclear, we attempted to contact relevant study authors to request or clarify these data.

Where data remained missing for the proportion of participants with dehisced wounds or participants with SSI, we assumed that if randomised participants were not included in the results section of the paper, their wound did not show dehiscence or they did not have a SSI (i.e. in the analysis, missing participants were considered in the denominator but not the numerator). When appropriate, we planned to conduct a completed case analysis as a sensitivity analysis and also planned to explore alternative scenarios using different assumptions about missing cases. In the event only one trial had very substantive numbers of participants who were absent from the reported results and, because of clinical considerations we considered an ITT analysis non‐conservative. We therefore conducted a completed case analysis and conducted a sensitivity analysis to explore the impact of excluding this trial from the meta‐analysis.

For continuous variables, for example, length of hospital stay, and for all secondary outcomes, we presented available data from the study reports/study authors, but we did not impute missing data. Where measures of variance were missing, we planned to calculate these if this were possible. When calculation was not possible, we attempted to contact study authors. Where these measures of variation were not available, we excluded the study from any relevant meta‐analyses that we conducted.

Assessment of heterogeneity

Assessment of heterogeneity can be a complex, multifaceted process. Firstly, 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 duration of follow‐up. We supplemented this assessment of clinical and methodological heterogeneity with information regarding statistical heterogeneity ‐ assessed using the Chi² test (we 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, can be interpreted as a low level of heterogeneity (Higgins 2003), and values of 75%, or more, indicate very high heterogeneity (Deeks 2011). However, these figures are only a guide, and it has been recognised that statistical tests and metrics may miss important heterogeneity ‐ thus, whilst these were assessed, the overall assessment of heterogeneity used these measures in combination with the methodological and clinical assessment of heterogeneity: see Data synthesis for further information about how we dealt with potential heterogeneity in the data analyses.

Assessment of reporting biases

Reporting biases arise when the dissemination of research findings is influenced by the nature and direction of results. Publication bias is one of a number of 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 (Sterne 2011). We presented funnel plots for meta‐analyses comprising 10 RCTs or more using Review Manager 5 (RevMan 2014). We also conducted Egger's test as a post‐hoc measure on the advice of peer reviewers.

Data synthesis

We combined details of included studies in narrative review according to type of comparator and contamination level of wound. We planned to group outcomes by time period but in practice found that this was not helpful (see Differences between protocol and review). We considered clinical and methodological heterogeneity, and undertook pooling when studies appeared appropriately similar in terms of wound type, intervention type, duration of follow‐up, and outcome type.

In terms of meta‐analytical approach, our default approach was to use the random‐effects model. We planned to only use a fixed‐effect approach if clinical heterogeneity was thought to be minimal and statistical heterogeneity was not statistically significant for the Chi‐² value and 0% for the I² assessment (Kontopantelis 2013). We adopted this approach as it is recognised that statistical assessments can miss potentially important between‐study heterogeneity in small samples, hence the preference for the more conservative random‐effects model (Kontopantelis 2012). Since either clinical or statistical heterogeneity indicated that a random‐effects analysis was appropriate in all cases, we did not use any fixed‐effect analyses. Where clinical heterogeneity was thought to be acceptable, or of interest, we planned that we would meta‐analyse even when statistical heterogeneity was high, but would have attempted to interpret the causes behind this heterogeneity. We planned to consider using meta‐regression for that purpose, if possible (Thompson 1999). In the event, heterogeneity was not sufficiently high to require this approach but we used some exploratory subgroup analyses to confirm that lower levels of heterogeneity were not a consequence of particular differences between interventions.

We presented data using forest plots, where possible. For dichotomous outcomes, we presented the summary estimate as a RR with 95% CI. If continuous outcomes were measured in the same way across studies, we presented a pooled difference in means with 95% CI; we had planned to pool standardised difference in means estimates where studies measured the same outcome, but use different methods. However the studies that reported continuous data all used the same unit of measurement. For time to event data, we planned to plot (and, if appropriate, pool) estimates of hazard ratios and 95% CIs, as presented in the study reports, using the generic inverse variance method in Review Manager 5 (RevMan 2014), however no time‐to event data were reported in included studies.

We obtained pooled estimates of treatment effect using Cochrane Review Manager 5 software (RevMan 2014).

'Summary of findings' tables

We presented the main results of the review in 'Summary of findings' tables. These tables present key information concerning the quality of the evidence, the magnitude of the effects of the interventions examined, and the sum of the available data for the main outcomes (Schünemann 2011a). The 'Summary of findings' tables also include an overall grading of the evidence related to each of the main outcomes using the GRADE (Grades of Recommendation, Assessment, Development and Evaluation) approach. The GRADE approach defines the quality 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 quality 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 2011b). GRADE was undertaken for all outcomes where it was possible to calculate an estimate of effect. We planned to present the following primary outcomes in the 'Summary of findings' tables:

surgical site infection (SSI);
wound dehiscence within 30 days of operation.

In addition we also included adverse events in the 'Summary of findings' tables; this was at the suggestion of peer reviewers as noted in Differences between protocol and review.

We did not produce a 'Summary of findings' table for comparisons where the data were limited. Instead we summarised the specified outcomes together with their GRADE assessment in an additional table, Table 4. This was done in order to make the 'Summary of findings' tables manageable and improve the readability of the review.

1. Summary of GRADE assessments for comparisons with limited data.

Comparison	Surgery	Participants (studies)	SSI RR (95% CI)	GRADE judgement: certainty of the evidence	Reason for downgrading
Icodextrin vs Ringer's solution	Clean‐contaminated (uterine)	426 (1 RCT) Trew 2011	2.89 (0.30 to 27.56)	Low	Downgraded twice for very serious imprecision
Povidone iodine vs Dermacyn	Clean (cardiac)	190 (1 RCT) Mohd 2010	2.80 (1.05 to 7.47)	Low	Downgraded once for high risk of bias and once for imprecision
Povidone iodine vs chlorhexidine	Dirty (peritonitis)	53 (1 RCT)¹ Vallance 1985	1.13 (0.78 to 1.63)	Very low	Downgraded twice for high risk of bias in multiple domains and once for imprecision
Cepharin vs cefoxitin	Clean‐contaminated (caesarean section)	132 (1 RCT)¹ Levin 1983	Not estimable (no events in either group)	No assessment possible	‐
Epicillin vs lincomycin	Contaminated (appendicitis)	162 (1 RCT)¹ Marti 1979	Not estimable (data not reported for groups)	No assessment possible	‐
Gentamicin vs clindamycin	Clean (breast)	51 (1 RCT)¹ Oller 2015	Not estimable (no events in either group)	No assessment possible	‐
Cephapirin versus moxalactam	Clean‐contaminated (caesarean section)	149 (total 360) (1 RCT)² Dashow 1986	1.69 (0.29 to 9.84)	Low	Downgraded twice for very serious imprecision
Cephapirin versus cefamandole	Clean‐contaminated (caesarean section)	134 (total 360) (1 RCT)² Dashow 1986	1.37 (0.24 to 7.95)	Low	Downgraded twice for very serious imprecision
Cephapirin versus ampicillin	Clean‐contaminated (caesarean section)	140 (total 360) (1 RCT)² Dashow 1986	7.00 (0.37 to 133.06)	Low	Downgraded twice for very serious imprecision
Cefamandole versus moxalactam	Clean‐contaminated (caesarean section)	143 (total 360) (1 RCT)² Dashow 1986	1.23 (0.18 to 8.52)	Low	Downgraded twice for very serious imprecision
Cefamandole versus ampicillin	Clean‐contaminated (caesarean section)	134 (total 360) (1 RCT)² Dashow 1986	5.46 (0.27 to 111.65)	Low	Downgraded twice for very serious imprecision
Moxalactam versus ampicillin	Clean‐contaminated (caesarean section)	149 (total 360) (1 RCT)² Dashow 1986	4.44 (0.22 to 90.88)	Low	Downgraded twice for very serious imprecision
Cefazolin versus cefamandole	Clean‐contaminated (caesarean section)	207 (1 RCT) Peterson 1990	4.58 (0.22 to 93.38)	Low	Downgraded twice for very serious imprecision

All irrigation compared with no irrigation for prevention of surgical site infection
Patient or population: participants undergoing clean, clean‐contaminated, contaminated or dirty surgical procedures Setting: hospitals  Intervention: irrigation of any type  Comparison: no irrigation
Outcomes	*Anticipated absolute effects^ (95% CI)**		Relative effect  (95% CI)	№ of participants  (studies)	Certainty of the evidence  (GRADE)	Comments
	Risk with no irrigation	Risk with irrigation
SSI	Study population: participants undergoing clean‐contaminated, contaminated or dirty surgical procedures		RR 0.87  (0.68 to 1.11)	6106  (14 RCTs)	⊕⊕⊝⊝  Low¹	On the basis of the included studies there is no clear difference between the intervention and comparison groups in the incidence of SSI.
	98 per 1000	85 per 1000  (67 to 108)
	Risk difference: 13 fewer SSI occur per 1000 with irrigation than with no irrigation (31 fewer to 10 more)
Wound dehiscence	Study population: participants undergoing clean procedures (split‐body design)		RR 1.17  (0.44 to 3.06)	30  (1 RCT)	⊕⊕⊝⊝  Low²	There is no clear difference between surgical sites treated with irrigation and those in the control condition. This is based on a single split‐body design with small numbers of participants.
	200 per 1000	234 per 1000  (88 to 612)
	Risk difference: 34 more wound dehiscences occur per 1000 with irrigation than with no irrigation (112 fewer to 412 more)
Adverse events	Study population: participants undergoing clean‐contaminated or dirty surgical procedures		RR 1.05 (0.76 to 1.44)	403 (3 RCTs)	⊕⊕⊝⊝  Low³	There is no clear difference in the number of adverse events between participants treated with irrigation and those in the control condition.
	247 per 1000	259 per 1000 (187 to 355)
	Risk difference: 12 more per 1000 (from 59 fewer to 108 more)
Adverse events: abscess formation	Study population: participants undergoing dirty or contaminated surgical procedures		RR 0.91 (0.54 to 1.54)	331 (3 RCTs)	⊕⊕⊕⊝ Moderate⁴	There is no clear difference in the number of adverse events between participants treated with irrigation and those in the control condition.
	149 per 1000	136 per 1000
	Risk difference: 13 fewer per 1000 (from 69 fewer to 80 more)
*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; SSI: surgical site infection
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

Irrigation with antibacterial compared with non‐antibacterial solution for prevention of surgical site infection
Patient or population: participants undergoing clean, clean‐contaminated, contaminated or dirty surgical procedures  Setting: hospitals  Intervention: irrigation with antibacterial solution (antiseptic or antibiotic)  Comparison: irrigation with solution without antibacterial properties
Outcomes	*Anticipated absolute effects^ (95% CI)**		Relative effect  (95% CI)	№ of participants  (studies)	Certainty of the evidence  (GRADE)	Comments
	Risk with non‐antibacterial	Risk with antibacterial
SSI	Study population: participants undergoing clean‐contaminated, contaminated or dirty surgical procedures		RR 0.57  (0.44 to 0.75)	5141  (30 RCTs)	⊕⊕⊝⊝  Low¹	The included studies found that there may be fewer SSIs in participants treated with antibacterial irrigation compared with those treated with non‐antibacterial irrigation.
	140 per 1000	80 per 1000  (62 to 105)
	Risk difference: 60 fewer SSI occur per 1000 with antibacterial irrigation than with non‐antibacterial (78 to 35 fewer)
Wound dehiscence	Study population: participants undergoing clean or clean‐contaminated surgical procedures		RR 1.26  (0.65 to 2.45)	660  (3 RCTs)	⊕⊝⊝⊝  Very low²	The effect of antibacterial compared with non‐antibacterial irrigation on wound dehiscence is very uncertain.
	45 per 1000	56 per 1000  (29 to 109)
	Risk difference: 11 more wound dehiscences occur per 1000 with antibacterial irrigation than with non‐antibacterial (16 fewer to 64 more)
Adverse events	Study population: participants undergoing clean, clean‐contaminated or dirty surgical procedures		RR 0.55 (0.22 to 1.34)	178 (3 RCTs)	⊕⊕⊝⊝  Low³	It is unclear whether there is a difference in the incidence of all adverse events between participants treated with antibacterial irrigation compared with those treated with non‐antibacterial irrigation.
	67 per 1000	37 per 1000 (15 to 90)
	Risk difference: 30 fewer adverse events occur per 1000 with antibacterial irrigation than with non‐antibacterial (53 fewer to 23 more)
Adverse events: abscess formation	Study population: participants undergoing clean‐contaminated, contaminated or dirty surgical procedures		RR 0.82 (0.42 to 1.62)	1309 (9 RCTs)	⊕⊝⊝⊝  Very low⁴	The effect of antibacterial compared with non‐antibacterial irrigation on abscess formation is very uncertain
	31 per 1000	25 per 1000 (13 to 50)
	Risk difference: 6 fewer abscesses form per 1000 with antibacterial irrigation than with non‐antibacterial (18 fewer to 19 more)
*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; SSI: surgical site infection
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 quality: 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 quality: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect  Very low quality: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect

Standard irrigation compared with pulsatile irrigation for prevention of surgical site infection
Patient or population: participants undergoing clean, clean‐contaminated, contaminated or dirty surgical procedures  Setting: hospital  Intervention: standard irrigation with saline  Comparison: pulsatile irrigation with saline
Outcomes	*Anticipated absolute effects^ (95% CI)**		Relative effect  (95% CI)	№ of participants  (studies)	Certainty of the evidence  (GRADE)	Comments
	Risk with standard irrigation	Risk with pulsatile irrigation
SSI	Study population: participants undergoing clean or clean‐contaminated surgical procedures		RR 0.34  (0.19 to 0.62)	484  (2 RCTs)	⊕⊕⊝⊝  Low¹	Included studies show that there may be fewer SSIs in participants treated with pulsatile saline irrigation compared with standard techniques; the evidence is low certainty due to high risk of biases in the study contributing the majority of participants and weight to the analysis.
	165 per 1000	56 per 1000  (31 to 103)
	Risk difference: 109 fewer SSI occur per 1000 with pulsatile irrigation than with standard (134 fewer to 62 fewer)
Wound dehiscence	Study population: participants undergoing clean‐contaminated surgical procedures		RR 0.31  (0.01 to 7.55)	128  (1 RCT)	⊕⊕⊝⊝  Low²	There is no clear difference in the incidence of wound dehiscence between groups treated with standard or pulsatile techniques of saline irrigation. Confidence intervals include both benefit and harm and are wide and fragile.
	16 per 1000	5 per 1000  (0 to 122)
	Risk difference: 11 fewer wound dehiscences occur per 1000 with pulsatile irrigation than with standard (16 fewer to 106 more)
Adverse events	Study population: participants undergoing clean‐contaminated surgical procedures		RR 1.31 (0.87 to 1.97)	128 (1 RCT)	⊕⊕⊝⊝  Low²	There is no clear difference in the incidence of adverse events between groups treated with standard or pulsatile techniques of saline irrigation. Confidence intervals include both benefit and harm and are wide and fragile.
	486 per 1000	371 per 1000
	Risk difference: 115 fewer adverse events occur per 1000 with pulsatile irrigation (360 fewer to 48 more)
Adverse events: abscess formation	There were no reported data on abscess formation
*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; SSI: surgical site infection
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

Study	Surgical category/type	Participants	Interventions	Definition of SSI	Follow‐up	SSI events	Risk ratio (95% CI)	Wound dehiscence risk ratio (95% CI)
Comparison of irrigation compared with no irrigation
Bourgeois 1985	Clean‐contaminated Caeasarean section	223	Antibiotic irrigation/saline irrigation No irrigation	NR
Buanes 1991	Dirty Perforated appendicitis	35	Saline postoperative irrigation No postoperative irrigation	Temperature > 38.5C for > 24 h plus localised, drainage‐confirmed accumulation of fluid	6 weeks	9/39 2/44	5.08 (1.17 to 22.09) Not included in pooled analysis ‐ intervention too different	NR
Cervantes‐Sanchez 2000	Contaminated Appendicitis	283	Saline irrigation No irrigation	Collection of pus or positive bacteriologic culture from wound discharge	4 weeks	11/127 39/156	0.25 (0.19 to 0.65)	NR
Cho 2004	Clean‐contaminated Gastrectomy	34	Saline irrigation No irrigation	Centers for Disease Control and Prevention criteria	2 weeks	1/17 3/17	0.33 (0.04 to 2.89)	NR
De Jong 1982	Mixed Abdominal/inguinal hernia	592	Antiseptic irrigation No irrigation	Purulent discharge seen within 4 weeks or culturing of fluid from the wound was positive	4 weeks	36/279 39/279	0.92 (0.61 to 1.41)	NR
Elliott 1986¹	Clean‐contaminated Caeasarean section	158	Antibiotic irrigation No irrigation	NR	6 weeks	0/80 1/78	0.33 (0.01 to 7.86)	NR
Gungorduk 2010	Clean‐contaminated Caeasarean section	520	Saline irrigation No irrigation	Wound drained purulent material/serosanguineous fluid plus induration, warmth and tenderness	6 weeks	17/260 19/260	0.89 (0.48 to 1.68)	NR
Harrigill 2003	Clean‐contaminated Caeasarean section	196	Saline irrigation No irrigation	Undue tenderness, erythema, discharge, or separation of the incision accompanying fever	NR	1/97 2/99	0.51 (0.05 to 5.54)	NR
Mahomed 2016	Clean‐contaminated Caeasarean section	3270	Antiseptic irrigation No irrigation	Abscess or wound draining pus or sero‐sanguinous fluid, or redness, induration, warmth and tenderness or general practitioner prescribed antibiotics	4 weeks	144/1520 147/1507	0.97 (0.78 to 1.21)	NR
Oleson 1980	Dirty Perforated appendicitis	33	Antibiotic irrigation/saline irrigation No irrigation	NR	Mean 8 d (5‐16)	5/20 4/10	0.63 (0.21 to 1.83)	NR
Ozlem 2015	Dirty Perforated appendicitis	14	Saline irrigation No irrigation	NR	NR	2/7 0/7	5.00 (0.28 to 88.53)	NR
Platt 2003	Clean Breast	30	Saline irrigation No irrigation	Wound discharge, invasive infection	8 weeks	0/30 0/30	Not estimable Not included in pooled analysis ‐ split‐body design	1.15 (0.44 to 3.06)
Schein 1990	Dirty Abdominal infection	87	Saline irrigation/ Antibiotic irrigation No irrigation	Discharge of pus	2 weeks	10/58 6/29	0.83 (0.34 to 2.07)	NR
Snow 2016	Mixed Appendix	83	Saline irrigation No irrigation	NR	6 weeks	0/40 0/41	Not estimable	NR
St Peter 2012	Dirty Appendix	220	Saline irrigation No irrigation	NR				NR
Tanaka 2015	Clean‐contaminated Liver resection	193	Saline irrigation No irrigation	Incisional or organ/space infection Incisional infection: clinically apparent cellulitis, induration, or purulent discharge. Organ/space infection: radiologic evidence of fluid collection necessitating drainage or antibiotic therapy	4 weeks	21/96 13/97	1.63 (0.87 to 3.07)	NR
Tanphiphat 1978	Contaminated Appendix	374	Antiseptic irrigation No irrigation	Collection of pus that emptied itself spontaneously or after incision	2 weeks	13/128 12/124	1.05 (0.50 to 2.21)	NR
Temizkan 2016	Clean‐contaminated Caeasarean section	430	Saline irrigation No irrigation	Partial or total separation of incision, plus purulent or serous wound discharge with induration, warmth, and tenderness	NR	1/215 2/215	0.50 (0.05 to 5.47)	NR
Tighe 1982	Contaminated Appendix	131	Antiseptic irrigation No irrigation Non‐antibacterial irrigation	Prescence of pus either spontaneously or on probing. All infections confirmed bacteriologically	NR	17/131 Results are not given by intervention group; no effect estimate calculable		NR
Viney 2012	Clean‐contaminated Caeasarean section	236	Saline irrigation No irrigation	NR				NR
Comparison of antibacterial irrigationwith non‐antibacterial irrigation
Al‐Shehri 1994	Mixed Appendicits	254	Antibiotic Saline	Purulent discharge in wound, regardless of culture results, or occurrence of serous discharge with positive culture	1 month	1/120 7/134	0.16 (0.02 to 1.28)	NR
Baker 1994	Clean‐contaminated Colorectal	330	Antiseptic Saline	Spontaneous or incisional discharge from wound, pus or serous fluid, with infective organism identified on culture	6 weeks	17/150 17/150	1.00 (0.53 to 1.88)	NR
Bourgeois 1985	Clean‐contaminated Caeasarean section	223	Antibiotic irrigation Saline irrigation (No irrigation)	NR				NR
Browne 1978	Dirty Peritonitis	35	Antiseptic irrigation Saline irrigation	NR				NR
Carl 2000	Clean‐contaminated	40	Antibiotic Saline	NR	4‐6 weeks	1/20 1/20	1.00 (0.07 to 14.90)	NR
Case 1987	Clean Breast	54	Antibiotic Saline	NR	6 weeks	0/23 1/30	0.43 (0.02 to 10.11)	0.43 (0.02 to 10.11)
Chang 2006	Clean Spinal	244	Antiseptic Saline	Superficial (above lumbosacral fascia) or deep (below lumbosacral fascia), early onset (within 2 weeks) or late onset (otherwise). Deep infections confirmed by laboratory parameters: erythrocyte sedimentation rate, level of C‐reactive protein, and positive biopsy culture	2 weeks, long‐term follow‐up to 19 months	0/120 6/124	0.08 (0.00 to 1.40) Only included in sensitivity analysis due to suspected data overlap with Cheng 2005	0.52 (0.05 to 5.62)
Cheng 2005	Clean Spinal	417	Antiseptic Saline	Unusual pain, tenderness, erythema, induration, fever, or wound drainage; investigated with erythrocyte sedimentation rate, C‐reactive protein, and bacteriological cultures from operative site or blood	2 weeks', long‐term follow‐up to mean 15.5 months	0/208 7/206	0.07 (0.00 to 1.015)	NR
Dashow 1986	Clean‐contaminated Caesarean	360	4 antibiotics Saline	Wound breakdown with positive culture or presence of cellulitis	NR	7/283 3/77	0.63 (0.17 to 2.40)	NR
Greig 1987	Mixed Colorectal	129	Antibiotic Saline	Discharge of pus from the wound "wound sepsis"	1 month	15/64 18/65	0.85 (0.47 to 1.53)	NR
Halsall 1981	Mixed Appendicitis	192	Antiseptic Saline	Wound discharging pus	4 weeks	18/99 29/93	0.58 (0.35 to 0.98)	NR
Kokavec 2008	Clean Orthopaedic	162	Antiseptic Saline	Positive bacteriological examination	6 weeks then mean 7.8 (2‐4) months	0/89 2/73	0.16 (0.01 to 3.37)	NR
Kubota 1999	Dirty Perforated appendicitis	16	Antiseptic Saline	NR	NR	1/8 4/8	0.25 (0.04 to 1.77)	NR
Kubota 2015	Dirty Perforated appendicitis	44	Antiseptic Saline	Infection at operation site, up to 30 d after surgery; confirmed causative pathogen(s) identical to those of appendicitis	30 d	0/24 4/20	0.09 (0.01 to 1.64)	NR
Levin 1983	Clean‐contaminated Caeasarean section	128	2 Antibiotics Saline	Purulent wound discharge with or without wound separation	8 weeks	0/85 3/43	0.07 (0.00 to 1.38)	NR
Lord 1983	Mixed Gastrointestinal/colorectal	200	Antibiotic Saline	NR	NR	3/100 9/100	0.33 (0.09 to 1.20)	NR
Magann 1993	Clean‐contaminated Caeasarean section	100	Antibiotic Saline	Hyperemic skin incision and fluctuant mass which when opened contained purulent material	NR	2/50 4/50	0.50 (0.10 to 0.50)	NR
Marti 1979	Contaminated Appendicitis	162	2 Antibiotics Saline	Septic complications with spontaneous or induced purulent discharge	4 d; longer follow‐up unclear	Results are not given by intervention group; no effect estimate calculable		NR
Mirsharifi 2008	Clean‐contaminated Cholecystectomy	102	Antibiotic Saline	Erythema, induration, tenderness, warmth, suppurative discharge	6 weeks	6/51 6/51	1.00 (0.35 to 2.89)	NR
Moylan 1968	Clean‐contaminated Abdominal	260	Antibiotic Saline	NR, wounds were monitored with daily photographs	Until discharge	12/124 23/116	0.49 (0.25 to 0.94)	NR
Neeff 2016	Clean‐contaminated Colorectal	197	Antiseptic Non‐antibacterial	NR	NR	19/101 22/96	0.82 (0.48 to 1.42)	NR
Oestreicher 1989	Mixed General surgery	540	Antiseptic Saline	NR	NR	16/267 15/273	1.09 (0.55 to 2.16)	NR
Oleson 1980	Dirty Perforated appendicitis	33	Antibiotic irrigation Saline irrigation No irrigation	NR	mean 8 d (5‐16)	3/10 2/10	1.50 (0.32 to 3.09)	NR
Oller 2015	Clean Breast	51	2 Antibiotics Saline	NR	NR	0/34 0/17	Not estimable	NR
Rambo 1972	Dirty Peritonitis	94	Antibiotic Saline	NR	NR	11/44 13/50	0.96 (0.48 to 1.92)	NR
Ruiz‐Tovar 2011	Clean‐contaminated Colorectal	128	Antibiotic Saline	NR	NR	6/64 27/64	0.22 (0.10 to 0.50)	NR
Ruiz‐Tovar 2012	Clean‐contaminated Colorectal	108	Antibiotic Saline	Presence of purulent discharge, confirmed with microbiologic culture	30 d	2/52 7/51	0.29 (0.06 to 1.31)	NR
Ruiz‐Tovar 2013	Clean Breast	40	Antibiotic Saline	NR	2 weeks	0/20 0/20	Not estimable	NR
Ruiz‐Tovar 2016a	Clean‐contaminated Colorectal	106	Antibiotic Saline	NR	30 d	2/52 7/52	0.20 (0.05 to 1.87)	NR
Ruiz‐Tovar 2016b	Clean‐contaminated Bariatric surgery	80	Antibiotic Saline	NR	30 d after discharge	NR		NR
Schein 1990	Dirty Abdominal infection	87	Antibiotic Saline (No irrigation)	Discharge of pus	2 weeks	5/29 5/29 (6/29)	1.00 (0.32 to 3.09)	NR
Silverman 1986	Mixed Gastrointestinal/colorectal	159	Antibiotic Saline	Discharge of pus	6 weeks	10/85 24/74	0.36 (0.19 to 0.71)	NR
Sindelar 1979	Mixed General Surgery	500	Antiseptic Saline	Pus discharged within 12 weeks or serous drainage from questionable wounds plus positive culture	12 weeks	7/242 39/258	0.19 (0.09 to 0.42)	NR
Takesue 2011	Clean‐contaminated Colorectal	400	Antiseptic Saline	National Nosocomial Infections Surveillance system	30 d (total 3 months)	19/180 29/183	0.67 (0.39 to 1.14)	1.44 (0.71 to 2.93)
Tighe 1982	Contaminated Appendix	131	Antiseptic irrigation Non‐antibacterial irrigation (No irrigation)	Prescence of pus either spontaneously or on probing. All infections confirmed bacteriologically	NR	7/131 Results are not given by intervention group; No effect estimate calculable		NR
Vallance 1985	Dirty Peritonitis	53	2 Antiseptics Saline	Pus in wound, sero‐sanguinous discharge, Inflammation or induration	1 month	23/29 10/16	0.61 (0.40 to 0.92)	NR
Comparisons of two different agents in the same class
Brown 2007	Clean‐contaminated Uterine	449	2 non‐antibacterials Icodextrin Ringer's solution	NR clearly; data on infection ambiguous				NR
Dashow 1986	Clean‐contaminated Caesarean	360	4 antibiotics (Saline) Cephapirin Cefamandole Moxalactam Ampicillin	Wound breakdown with positive culture or presence of cellulitis	NR	3/70 2/64 2/79 0/70	Cephapirin: cefamandole 1.37 (0.24 to 7.95) Cephapirin: moxalactam 1.69 (0.29 to 9.84) Cephapirin: ampicillin 7.00 (0.37 to 133.06) Cefamandole: moxalactam 1.23 (0.18 to 8.52) Cefamandole: ampicillin 5.46 (0.27 to 111.65) Moxalactam: ampicillin 4.44 (0.22 to 90.88)	NR
Levin 1983;	Clean‐contaminated Caesarean	128	2 antibiotics (Saline) Cephapirin cefoxitin	Purulent wound discharge with or without wound separation	8 weeks	0/44 0/41	Not estimable; zero events	NR
Marti 1979	Contaminated Appendicitis	162	2 antibiotics (Saline) Epicillin Lincomycin	Septic complications with spontaneous or induced purulent discharge	4 d; longer follow‐up unclear	Not estimable; number of participants and events per group not reported		NR
Mohd 2010;	Clean Cardiac	190	2 antiseptics Povidone iodine Dermacyn	Centers for Disease Control and Prevention criteria	6 weeks	14/90 5/88	2.80 (1.05 to 7.47)	NR
Oller 2015	Clean Breast	51	2 antibiotics Clindamycin Gentamicin	NR	NR	0/17 0/17	Not estimable; zero events	NR
Peterson 1990	Clean‐contaminated Caesarean	207 113 in relevant groups	2 antibiotics Cefazolin Cefamandole	Presence of cellulitis and/or purulent exudate	> 2 weeks	2/59 0/54	4.58 (0.22 to 93.38)	NR
Shimizu 2011	Clean Brain	20	2 non‐antibacterials Saline Artificial CSF	NR				NR
Trew 2011	Clean‐contaminated Uterine	498	2 non‐antibacterials Icodextrin Ringer's solution	NR	4‐16 weeks	3/217 1/209	2.89 (0.30 to 27.56)	NR
Vallance 1985	Dirty Peritonitis	53	2 antiseptics (Saline) Povidone iodine Chlorhexidine	Pus in wound, sero‐sanguinous discharge, Inflammation or induration	1 month	4/16 4/13	1.13 (95% CI 0.78 to 1.63)	NR
Comparison of pulsatile versus standard irrigation delivery
Hargrove 2006	Clean Orthopaedic	356	Pulsatile saline Standard saline	Nosocomial Infection National Surveillance Survey	30 days or discharge	9/164 30/192	0.35 (0.17 to 0.72)	NR
Nikfarjam 2014	Clean‐contaminated Abdominal	137	Pulsatile saline Standard saline	Purulent drainage, with or without laboratory confirmation; organisms isolated from aseptically obtained culture of fluid or tissue; at least 1 of the following: pain or tenderness, localised swelling, redness, or heat and incision is deliberately opened by surgeon, unless incision is culture‐negative; diagnosis of superficial incisional SSI by surgeon or attending physician	1 month	4/66 12/62	0.31 (0.11 to 0.92)	0.31 (0.01 to 7.55)

Comparison	Subgroup basis	Pre‐specified or exploratory	Subgroups used	Subgroup results  RR (95% CI)	I² & Chi² subgroup differences	I² & Chi² overall
Irrigation vs no irrigation	Surgical classification	Pre‐specified	Clean‐contaminated Contaminated/Dirty/Mixed	1.00 (0.82, 1.21) 0.74 (0.47 to 1.16)	I² = 29.1%. Chi² = 1.41	I² = 28% Chi² = 16.58
Irrigation vs no irrigation	Type of irrigation	Exploratory	Non‐antibacterial Antiseptic Antibiotic	0.80 (0.46 to 1.41) 0.97 (0.81 to 1.17) 0.92 (0.42 to 1.99)	I² = 0% Chi² = 0.39	I² = 28% Chi² = 16.58
Antibacterial vs non‐antibacterial	Surgical classification	Pre‐specified	Clean Clean‐contaminated Contaminated/Dirty/Mixed	0.17 (0.03 to 0.89) 0.57 (0.40 to 0.79) 0.61 (0.40 to 0.92)	I²= 9.7% Chi² = 2.21	I² = 53% Chi² = 56.94
Antibacterial vs non‐antibacterial	Type of irrigation	Exploratory	Antiseptic Antibiotic	0.63 (0.40 to 0.95) 0.57 (0.44 to 0.75)	I²= 0% Chi² = 0.38	I² = 53% Chi² = 56.94

Study Surgical category/type	Participants (N) Follow‐up	Interventions	Mortality  RR (95% CI)	Systemic antibiotics  RR (95% CI)	Antibiotic resistance  RR (95% CI)	Adverse events  RR (95% CI)	Reoperation  RR (95% CI)	Readmission  RR (95% CI)	Length of stay (days (95% CI))
Irrigation compared with no irrigation
Bourgeois 1985 Clean‐contaminated Caeasarean section	223 6 weeks	Antibiotic irrigation/Saline irrigation No irrigation	‐	‐	‐	Specific complication only	‐	‐	Difference in means ‐0.46 (‐0.64 to ‐0.29)
Buanes 1991 Dirty Perforated appendicitis	85 6 weeks	Saline postoperative irrigation No postoperative irrigation	‐	‐	‐	‐	‐	‐	Medians 5 (3‐11) vs 5 (4‐12)
Cervantes‐Sanchez 2000 Contaminated Appendicitis	283 4 weeks	Saline irrigation No irrigation	‐	‐	‐	No group data	‐	‐	‐
Cho 2004 Clean‐contaminated Gastrectomy	34 2 weeks (primary outcome)	Saline irrigation No irrigation	No secondary outcomes were reported
De Jong 1982 Mixed Abdominal/inguinal hernia	592 4 weeks (primary outcome)	Antiseptic irrigation No irrigation	No secondary outcomes were reported
Elliott 1986¹ Clean‐contaminated Caeasarean section	158 6 weeks	Antibiotic irrigation No irrigation	‐	‐	‐	Specific complication only	‐	‐	Difference in means ‐0.20 (‐0.57 to 0.17)
Gungorduk 2010 Clean‐contaminated Caeasarean section	520 6 weeks	Saline irrigation No irrigation	‐	‐	‐	‐	‐	‐	Difference in means 0.01 (‐0.03 to 0.05)
Harrigill 2003 Clean‐contaminated Caeasarean section	196 NR	Saline irrigation No irrigation	‐	‐	‐	Overall RR 1.10 (0.55 to 2.22)	‐	‐	Difference in means 0.10 (‐0.17 to 0.37)
Mahomed 2016 Clean‐contaminated Caeasarean section	3270 4 weeks	Antiseptic irrigation No irrigation	‐	‐	‐	‐	RR 0.77 (0.29 to 2.07)	RR 1.29 (0.81 to 2.06)	‐
Oleson 1980 Dirty Perforated appendicitis	33 mean 8 days (5‐16)	Antibiotic irrigation/Saline irrigation No irrigation	‐	‐	‐	Abscess RR 0.17 (0.01 to 3.94)	‐	‐	Medians 14 (8‐22) vs 13 (9‐22)
Ozlem 2015 Dirty Perforated appendicitis	14 NR	Saline irrigation No irrigation	‐	‐	‐	Overall RR 1.00 (0.08 to 13.02) Abscess but no group data	‐	‐	‐
Platt 2003 Clean Breast	30 8 weeks	Saline irrigation No irrigation	‐	‐	‐	‐	‐	‐	‐
Schein 1990 Dirty Abdominal infection	87 2 weeks	Saline irrigation Antibiotic irrigation No irrigation	RR 0.75 (0.30 to 1.90)	‐	‐	‐	‐	‐	Difference in means not estimable 11.5 vs 13
Snow 2016 Mixed Appendix	83 6 weeks	Saline irrigation No irrigation	‐	‐	‐	Abscess RR 1.02 (0.15 to 6.93)	‐	‐	Medians 2.0 (1‐3) vs 2.0 (1‐2.25)
St Peter 2012 Dirty Appendix	220 2‐4 weeks	Saline irrigation No irrigation	‐	‐	‐	Abscess RR 0.95 (0.55 to 1.65)	RR 0.33 (0.01 to 8.09)	RR 0.14 (0.01 to 2.73)	Difference in means ‐0.10 (‐0.85 to 0.65)
Tanaka 2015 Clean‐contaminated Liver resection	193 4 weeks	Saline irrigation No irrigation	RR 2.02 (0.36 to 2.04)	‐	‐	Overall RR 1.04 (0.72 to 1.49)	‐	‐	Difference in means 0.00 (‐3.74 to 3.74)
Tanphiphat 1978 Contaminated Appendix	374 2 weeks	Antiseptic irrigation No irrigation	No secondary outcomes were reported
Temizkan 2016 Clean‐contaminated Caeasarean section	430 NR	Saline irrigation No irrigation	No secondary outcomes were reported
Tighe 1982 Contaminated Appendix	131 NR	Antiseptic irrigation No irrigation Non‐antibacterial irrigation	‐	53/131 participants "distributed evenly across the groups"	‐	‐	‐	‐	No group data
Viney 2012 Clean‐contaminated Caeasarean section	236 NR	Saline irrigation No irrigation	‐	‐	‐	‐	‐	‐	Median discharge day: 3 in both groups
Antibacterial irrigation vs non‐antibacterial irrigation
Al‐Shehri 1994 Mixed Appendicits	254 1 month	Antibiotic Saline	‐	‐	‐	Abscess RR not estimable 0 events			No group data
Baker 1994 Clean‐contaminated Colorectal	330 6 weeks	Antiseptic Saline	RR 1.00 (0.25 to 3.92)	‐	‐	Abscess RR 2.0 (0.18 to 21.82)			No group data
Bourgeois 1985 Clean‐contaminated Caeasarean section	223 6 weeks	Antibiotic irrigation Saline irrigation (No irrigation)	‐	‐	‐	Specific complication only	‐	‐	Difference in means ‐1.08 (‐1.25 to ‐0.92)
Browne 1978 Dirty Peritonitis	35 NR	Antiseptic irrigation Saline irrigation	RR 7.39 (0.41 to 133.24)	‐	‐	‐			‐
Carl 2000 Clean‐contaminated Caeasarean section	40 4‐6 weeks	Antibiotic Saline	‐	‐	‐	‐			‐
Case 1987 Clean Breast	54 6 weeks	Antibiotic Saline	‐	‐	‐	‐			‐
Chang 2006 Clean Spinal	244 2 weeks, long‐term follow‐up to 19 months	Antiseptic Saline	‐	All 6 participants with SSI received these; all in saline group	5/6 infections positive for MRSA	‐			‐
Cheng 2005 Clean Spinal	417 2 weeks long ‐term follow ‐up to mean 15.5 months	Antiseptic Saline	‐	‐	‐	‐			‐
Dashow 1986 Clean‐contaminated Caeasarean section	360 NR	4 antibiotics Saline	‐	‐	‐	Abscess RR not estimable 0 events			‐
Greig 1987 Mixed Colorectal	129 1 month	Antibiotic Saline	No secondary outcomes were reported
Halsall 1981 Mixed Appendicitis	192 4 weeks	Antiseptic Saline	‐	‐	‐	‐			Difference in means not estimable (6.4 vs 6.6)
Kokavec 2008 Clean Orthopaedic	162 mean 7‐8 months (range 2‐14 months) (primary outcome)	Antiseptic Saline	No secondary outcomes were reported						‐
Kubota 1999 Dirty Perforated appendicitis	16 NR	Antiseptic Saline	‐	‐	‐	Abscess RR 0.33 (0.02 to 7.14)			Difference in means ‐10.60 (‐19.06 to ‐2.14)
Kubota 2015 Dirty Perforated appendicitis	44 30 days	Antiseptic Saline	‐	‐	‐	Abscess RR 0.83 (0.06 to 12.49)			Difference in means ‐0.70 (‐3.31 to 1.91)
Levin 1983 Clean‐contaminated Caeasarean section	128 8 weeks	Antibiotic Saline	‐	‐	‐	Specific complication only			Difference in means ‐0.35 (‐1.06 to 0.36)
Lord 1983 Mixed Gastrointestinal/colorectal	200 NR	Antibiotic Saline	RR 1.67 (0.41 to 6.79)	‐	Specific organisms	Specific complication only			‐
Magann 1993 Clean‐contaminated Caeasarean section	100 NR	Antibiotic Saline	‐	‐	‐	Specific complication only			‐
Marti 1979 Contaminated Appendicitis	162 4 days; longer follow‐up unclear	Antibiotic Saline	‐	‐	‐	Specific complication only			‐
Mirsharifi 2008 Clean‐contaminated Cholecystectomy	102 6 weeks	Antibiotic Saline	No secondary outcomes were reported
Moylan 1968 Clean‐contaminated Abdominal	260 Until discharge	Antibiotic Saline	‐	‐	Kanamycin resistance Kanamycin: 12/12 Saline: "over half" of 23	Specific complication only			‐
Neeff 2016 Clean‐contaminated Colorectal	197 NR	Antiseptic Saline	No secondary outcomes were reported
Oestreicher 1989 Mixed General surgery	540 NR	Antiseptic Saline	No secondary outcomes were reported						‐
Oleson 1980 Dirty Perforated appendicitis	33 Mean 8 days (5‐16	Antibiotic irrigation Saline irrigation No irrigation	‐	‐	‐	Abscess RR not estimable 0 events			Medians 13 (9‐20 13 (10‐22)
Oller 2015 Clean Breast	51 NR	Antibiotic 1/ Antibiotic 2 Saline	RR not estimable, 0 events	‐	‐	‐			Medians 3 (1‐3) 3 (1‐3)
Rambo 1972 Dirty Peritonitis	94 NR	Antibiotic Saline	RR 0.71 (0.25 to 2.01)	‐	Specific organisms	Abscess grouped with another event ‐ not estimable			‐
Ruiz‐Tovar 2011 Clean‐contaminated Colorectal	128 NR	Antibiotic Saline	No secondary outcomes were reported
Ruiz‐Tovar 2012 Clean‐contaminated Colorectal	108 30 days	Antibiotic Saline	RR 0.50 (0.05 to 5.35)	‐	‐	Abscess RR 0.14 (0.01 to 2.65)			Medians 6 (5‐32) 6.5 (5‐14)
Ruiz‐Tovar 2013 Clean Breast	40 2 weeks	Antibiotic Saline	RR not estimable, 0 events	‐	‐	Overall RR not estimable 0 events			Medians 3 (1‐3) 3 (1‐3)
Ruiz‐Tovar 2016a Clean‐contaminated Colorectal	106 30 days	Antibiotic Saline	RR 1.00 (0.06 to 15.57)	‐	‐	Specific complication only			Medians 6.5 (5‐14) 6 (5‐32)
Ruiz‐Tovar 2016b Clean‐contaminated Bariatric surgery	80 30 days	Antibiotic Saline	RR 0.33 (0.01 to 7.95)	‐	‐	Overall RR 0.50 (0.05 to 5.30)			‐
Schein 1990 Dirty Abdominal infection	87 2 weeks	Antibiotic Saline	RR 0.50 (0.14 to 1.81)	‐	‐	Overall RR 0.56 (0.21 to 1.46) Abscess RR 0.33 (0.01 to 7.86)			Difference in means not estimable 10 vs 13
Silverman 1986 Mixed Gastrointestinal/colorectal	159 6 weeks	Antibiotic Saline	‐	‐	‐	Abscess RR 0.96 (0.43 to 2.13) Specific additional complication	RR 6.10 (0.32 to 116.28)		‐
Sindelar 1979 Mixed General Surgery	500 12 weeks	Antiseptic Saline	No secondary outcomes were reported
Takesue 2011 Clean‐contaminated Colorectal	400 30 days (total 3 months)	Antiseptic Saline	‐	‐	MRSA 4/14 vs 8/24 MSSA 0/14 vs 3/24	‐			‐
Tighe 1982 Contaminated Appendix	131 NR	Antiseptic Non‐antibacterial (No irrigation)	‐	53/131 participants "distributed evenly across the groups"	‐	‐	‐	‐	No group data
Vallance 1985 Dirty Peritonitis	53 1 month	Antiseptic Saline	RR 0.61 (0.17 to 2.16)	‐	‐	‐			Difference in means ‐0.70 (‐3.32 to 1.92)
Comparisons of two different agents in the same class
Brown 2007 Clean‐contaminated Uterine	449 28‐56 days	2 non‐antibacterials Icodextrin Ringer's solution	RR not estimable ‐ 0 events	‐	‐	Total: RR 0.99 (0.96 to 1.02) Treatment‐related RR 1.42 (0.98 to 2.05) Serious RR 1.20 (0.80 to 1.78) Serious treatment‐related RR 0.71 (0.29 to 1.73)	‐	‐	‐
Dashow 1986 Clean‐contaminated Caeasarean section	360 NR	4 antibiotics (Saline) Cephapirin Cefamandole Moxalactam Ampicillin	‐	‐	‐	Abscess: no effect estimate calculable ‐ 0 events Other specific events	‐	‐	‐
Levin 1983 Clean‐contaminated Caeasarean section	128 8 weeks	2 antibiotics (Saline) Cephapirin Cefoxitin	‐	‐	‐	Specific event data only	‐	‐	Difference in means 0.10 (‐0.78 to 0.58)
Marti 1979 Contaminated Appendicitis	162 4 days; longer follow‐up unclear	2 antibiotics (Saline) Epicillin Lincomycin	‐	‐	‐	1 abscess in antibiotic groups; no group data	‐	‐	‐
Mohd 2010 Clean Cardiac	190 6 weeks	2 antiseptics Povidone iodine Dermacyn	4 deaths but no group data; group data for composite outcome with reopening of chest	‐	‐	‐	RR 8.80 (0.48 to 161.11)	‐	‐
Oller 2015 Clean Breast	51 NR	2 antibiotics Clindamycin Gentamicin	RR not estimable, 0 events	‐	‐	‐	‐	‐	Median 3 (1‐3) in each group
Peterson 1990 Clean‐contaminated Caeasarean section	207 113 in relevant groups 2 weeks + (primary outcome)	2 antibiotics Cefazolin Cefamandole	No secondary outcomes were reported
Shimizu 2011 Clean Brain	20 10 days	2 non‐antibacterials Saline Artificial CSF	‐	‐	‐	2 participants in each group, included MRI data. RR not calculated	‐	‐‐	‐
Trew 2011 Clean‐contaminated Uterine	498 4‐16 weeks	2 non‐antibacterials Icodextrin Ringer's solution	RR not estimable ‐ 0 events	‐		Total: RR 0.95 (0.73 to 1.24) Treatment‐related RR 1.16 (0.60 to 2.23)	‐	‐	‐
Vallance 1985 Dirty Peritonitis	53 1 month	2 antiseptics (Saline) Povidone iodine Chlorhexidine	RR 0.45 (0.05 to 3.90) within 4 days, no group data for later events	‐	‐	‐	‐	‐	Difference in means 3.30 (0.53 to 3.90)
Comparison of pulsatile versus standard irrigationdelivery
Hargrove 2006 Clean Orthopaedic	356 30 days or discharge	Pulsatile saline Standard saline	No group data	‐	No group data "half" SSI positive for MRSA	‐	‐	‐	‐
Nikfarjam 2014 Clean‐contaminated Abdominal	137 1 month	Pulsatile saline Standard saline	‐	No group data: 14/16 SSI treated	Qualitative data on organisms isolated	Complications, not wound infections RR 1.31 (0.87 to 1.97)	RR 0.56 (0.14 to 2.26)	RR 1.41 (0.53 to 3.73)	Median 9 (5 ‐45) 9 (4‐71)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 SSI	14	6106	Risk Ratio (M‐H, Random, 95% CI)	0.87 [0.68, 1.11]
1.1 clean or clean‐contaminated	7	4801	Risk Ratio (M‐H, Random, 95% CI)	1.00 [0.82, 1.21]
1.2 contaminated or dirty	7	1305	Risk Ratio (M‐H, Random, 95% CI)	0.74 [0.47, 1.16]
2 Adverse events	3	403	Risk Ratio (M‐H, Random, 95% CI)	1.05 [0.76, 1.44]
3 Abscess	3	331	Risk Ratio (M‐H, Random, 95% CI)	0.91 [0.54, 1.54]
4 Mortality	2	280	Risk Ratio (M‐H, Random, 95% CI)	0.86 [0.36, 2.04]
5 Hospital stay	7	1597	Mean Difference (IV, Random, 95% CI)	‐0.13 [‐0.38, 0.12]
6 Return to theatre (reoperation)	2	3247	Risk Ratio (M‐H, Random, 95% CI)	0.72 [0.28, 1.84]
7 Readmission to hospital	2	3247	Risk Ratio (M‐H, Random, 95% CI)	0.70 [0.10, 4.90]

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 SSI	30	5141	Risk Ratio (M‐H, Random, 95% CI)	0.57 [0.44, 0.75]
1.1 clean	4	680	Risk Ratio (M‐H, Random, 95% CI)	0.16 [0.03, 0.89]
1.2 clean‐contaminated	13	2210	Risk Ratio (M‐H, Random, 95% CI)	0.57 [0.40, 0.79]
1.3 contaminated or dirty	13	2251	Risk Ratio (M‐H, Random, 95% CI)	0.61 [0.40, 0.92]
2 Wound dehiscence	3	660	Risk Ratio (M‐H, Random, 95% CI)	1.26 [0.65, 2.45]
3 Adverse events	3	178	Risk Ratio (M‐H, Random, 95% CI)	0.55 [0.22, 1.34]
4 Abscess	9	1309	Risk Ratio (M‐H, Random, 95% CI)	0.82 [0.42, 1.62]
5 Mortality	11	1121	Risk Ratio (M‐H, Random, 95% CI)	0.81 [0.48, 1.36]
6 Hospital stay	7	635	Mean Difference (IV, Random, 95% CI)	‐0.85 [‐1.60, ‐0.09]
7 Return to theatre (reoperation)	2	403	Risk Ratio (M‐H, Random, 95% CI)	1.26 [0.12, 13.60]

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Mortality	2	875	Risk Ratio (M‐H, Fixed, 95% CI)	0.0 [0.0, 0.0]
2 Adverse events	2	875	Risk Ratio (M‐H, Random, 95% CI)	0.99 [0.96, 1.02]
3 Treatment‐related adverse events	2	875	Risk Ratio (M‐H, Random, 95% CI)	1.35 [0.98, 1.86]

Methods	2‐arm RCT Setting: NR; appears to be single hospital in Saudi Arabia Participants reportedly followed up for 1 month, no additional details
Participants	254 adults and children (aged 5‐80 years, mean age 21 (Group I) and 24 years (Group II)) undergoing appendectomy for acute appendicitis were randomised; 249 analysed Inclusion criteria: people undergoing appendectomy through gridiron incision for clinically suspected acute appendicitis Exclusion criteria: allergy to ampicillin; systemic diseases requiring systemic antibiotic administration
Interventions	Group I: (saline): wound irrigation with 100 mL normal sterile saline at closure (134 participants randomised; 132 analysed; 2 participants withdrawn post‐randomisation) Group II: (Ampicillin): wound irrigation with 1 g Ampicillin powder dissolved in 100 mL normal sterile saline (120 participants randomised; 117 analysed; 3 participants withdrawn post‐randomisation) Co‐interventions: IV metronidazole (500 mg for adults; 15 mg/kg for children) and gentamicin (75 mg for adults and 1.5 mg/kg for children) 1 h before surgery. If appendix was found to be gangrenous or perforated antibiotics were continued for 5 ds postoperatively.
Outcomes	Primary outcome: SSI (defined as presence of purulent discharge in wound, regardless of culture results, or as occurrence of serous discharge with a positive culture) within 1 month Group I (Saline): 7/132 (134 randomised) Group II (Ampicillin): 1/117 (120 randomised) Secondary outcome: adverse events including abscess: Abscess Group I (saline): 0/132 Group II (Ampicillin): 0/117 Other specific post‐operative complications were reported but total number of participants with adverse events was not clear. Secondary outcome: hospital stay: reported to be reduced by 2.5 d by avoidance of wound infection. Median reported for participants with (5.5, range 3‐11 d) and without infection (3.0, range 2‐11 d) but not for each treatment group.
Notes	Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "254 patients fulfilled the criteria and were randomized into two groups using sealed envelopes" Comment: no information on how the randomisation sequence was generated.
Allocation concealment (selection bias)	Unclear risk	Quote: "254 patients fulfilled the criteria and were randomized into two groups using sealed envelopes that were opened intraoperatively" Comment: although sealed envelopes were used it is not clear that they were opaque or that the allocation sequence was fully concealed at all times.
Blinding of participants and personnel (performance bias)   All outcomes	High risk	Comment: no direct quote but it is clear that personnel were made aware of allocation once the envelopes were opened. Unclear if participants were aware
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Comment: no direct quote but it is unclear whether the outcome assessment was performed by individuals aware of group allocation.
Incomplete outcome data (attrition bias)   All outcomes	High risk	Comment: there were a small number of post‐randomisation exclusions for protocol violations described. However there were low numbers of events relative to these exclusions, increasing the risk of attrition bias impacting the results.
Selective reporting (reporting bias)	Unclear risk	Comment: rhe data for one of the secondary outcomes (bed‐stay) were not reported on a per‐group base making this outcome difficult to evaluate.
Other bias	Unclear risk	Comment: there was no evidence of other sources of bias but reporting was not clear enough to be certain.

Methods	2‐arm RCT Setting: single centre; 1 surgical unit in UK Follow‐up: close monitoring during hospital stay; full inquiry into possible infection signs at 6‐week outpatient clinic follow‐up
Participants	330 participants undergoing elective colorectal surgery (mean ages 61 (Group I) and 63 years (Group II)); 300 analysed Inclusion criteria: participants undergoing elective colorectal surgery Exclusion criteria: NR
Interventions	Group I (taurolidine PVP): peritoneal lavage in 2 stages with 250 mL 2% taurolidine in 5% PVP (150 participants) Group II (saline): peritoneal lavage in 2 stages with 250 mL normal saline (150 participants) In each group 250 mL lavage solution diluted in a further 250 mL normal saline was placed in the abdomen as a washout and then removed with suction. This was followed by instillation of a second 250 mL undiluted lavage solution, which was left in the abdomen. If abdominal drains were present these were clamped for at least 20 min. Cointerventions: all participants (except 11 who had severe constricting colonic lesions and were in imminent danger of bowel obstruction) received up to 8 doses of magnesium sulphate (4 g by mouth) for 48 h starting 72 h before surgery followed by 2 sachets of sodium picosulphate (Picolax; Fering Pharmaceutical, Feltham, UK) given in the 24 h immediately before surgery. Participants with severe constricting colonic lesions were prepared according to the wishes of the surgeon; 8 received Klean‐Prep (Norgine, Oxford, UK) in place of Picolax and 3 no preparation. All participants received cefotaxime 1 g and metronidazole 500 mg IV at induction of anaesthesia, and 8 h and 16 h later. 5 participants with penicillin allergy received gentamicin 160 mg on induction, and 120 mg at 8 h and 16 h after induction; doses were individually adjusted according to body mass, renal function and age.
Outcomes	Primary outcome: SSI (defined as spontaneous or incisional discharge from the wound, either of pus or serous fluid, with an infective organism positively identified on culture) Group I (taurolidine PVP): 17/150 (10 superficial, 7 deep) Group II (saline): 17/150 (12 superficial, 5 deep) Secondary outcome: 30‐day mortality Group I (taurolidine PVP): 4/150 Group II (saline): 4/150 Secondary outcome: adverse events including abscess: Pelvic abscess Group I (taurolidine PVP): 2/150 Group II (saline): 1/150 Other specific post‐operative complications were reported but total number of participants with adverse events was not clear. Secondary outcome: length of hospital stay Group I (taurolidine PVP): median 11 d for 133 participants without infection; 18 d for 17 with infection (paper reports N = 134, error suspected) Group II (saline): median 11 d for 133 participants without infection; 18 d for 17 with infection (mean NR, range NR)
Notes	Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "This paper reports a randomized controlled trial.....Bottles of lavage fluid were dispensed in identical containers according to a computer‐generated randomized code held by the hospital pharmacy with no stratification for severity of contamination or procedure. " Comment: appears there was a computer‐generated randomisation sequence
Allocation concealment (selection bias)	Unclear risk	Quote: "Bottles of lavage fluid were dispensed in identical containers according to a computer‐generated randomized code held by the hospital pharmacy with no stratification for severity of contamination or procedure." Comment: although the allocation sequence was held by the hospital pharmacy it is not clear whether it was adequately concealed.
Blinding of participants and personnel (performance bias)   All outcomes	Low risk	Quote: "Bottles of lavage fluid were dispensed in identical containers according to a computer‐generated randomized code held by the hospital pharmacy... The trial and control solutions were indistinguishable to users." Comment: personnel appear to have been blinded; although there is no direct information on participants it is likely that they were also blinded.
Blinding of outcome assessment (detection bias)   All outcomes	Low risk	Quote: "All patients were monitored closely after operation until hospital discharge for clinical signs of abdominal sepsis and wound infection by an independent (non‐operating) trained assessor (J.AJ.)." Comment:
Incomplete outcome data (attrition bias)   All outcomes	High risk	Quote: "Sixteen patients were withdrawn from the trial after consent because the operative procedure performed did not constitute elective colorectal surgery ....... A further eight patients were withdrawn as lavage was not undertaken for logistical reasons, such as breakage of solution bottles. A further six patients were withdrawn at the time of surgery because of overt sepsis or severe faecal spillage, which rendered the intraoperative lavage a therapeutic rather than a prophylactic measure. Thus 300 patient reports were available for analysis." Comment: almost 10% of randomised participants were not included in the analysis. Although full reasons are given for this the number of withdrawals is almost equivalent to the number of events.
Selective reporting (reporting bias)	Low risk	Comment: the data for one of the secondary outcomes (bed‐stay) were not fully reported (measure of variance lacking) but no other evidence of selective reporting
Other bias	Unclear risk	Comment: there was no evidence of other sources of bias but reporting was not clear enough to be certain.

Methods	Parallel‐group RCT Setting: single hospital in USA Follow‐up: 6 weeks (review of records after discharge)
Participants	223 women undergoing cesarean section Inclusion criteria: women delivered by caesarean section Exclusion criteria: allergy to penicillin or cephalosporins, taken an antibiotic within 7 d of surgery or required antibiotics around time of surgery for other reasons. Participants with temperature elevated to 38^oC or with foul amniotic fluid prior to or immediately after surgery were considered to have infection and excluded. High risk and low risk participants were separated according to duration of labor prior to cesarean section, with 6 h arbitrarily chosen as the division point. Each group contained both high risk (more than 6 h labour) and low risk (less than 6 h labour) participants
Interventions	Group I: irrigation with 2 g cefamandole in 1000 mL normal saline (73 participants) Group II: irrigation with 1000 mL normal saline (75 participants) Group III: no irrigation (75 participants)
Outcomes	Secondary outcome: length of stay Group I: low risk: 5.2 (0.3) d (N = 46); high risk: 5.3 (0.2) (N = 27) Group II: low risk: 5.9 (0.4) d (N = 40); high risk 6.8 (0.6) (N = 35) Group III: low risk 5.8 (0.3) d (N = 44); high risk: 6.9 (0.4) (N = 31) Secondary outcome: adverse events Only a specific event (metritis) was reported Group I: low risk: 2 (4.3% of 46); high risk: NR Group II: low risk: 4 (10% of 40); high risk: NR Group III: low risk: 9 (20.5% of 44); high risk: NR Infection data were also reported but were not clearly SSI and were not reported for all participants Group I: low risk: NR; high risk: 3 (11.1% of 27) Group II: low risk: NR; high risk: 17 (48.6% of 35) Group III: low risk: NR; high risk: 17 (54.8% of 31)
Notes	Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "members of each group were then assigned to a cohort according to a computer‐generated table of random numbers under the direction of the hospital pharmacy" Comment: appropriate method used to generate randomisation sequence; randomisation stratified by duration of labour: > 6 h vs < 6 h
Allocation concealment (selection bias)	Unclear risk	Quote: "under the direction of the hospital pharmacy" Comment: unclear whether adequate methods were used to conceal allocation
Blinding of participants and personnel (performance bias)   All outcomes	High risk	Quote: "Physicians who performed the operation and provided postoperative care were unaware of the type of irrigation provided" Comment: physicians were unaware of the type of irrigation used but are likely to have been aware of whether irrigation was used or not. It is unclear whether participants were aware of treatment allocation.
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Quote: "Patients were followed postoperatively by the resident and attending physicians on service" Comment: not clear whether outcomes were determined by personnel blinded to treatment allocation.
Incomplete outcome data (attrition bias)   All outcomes	Unclear risk	Quote: "of all 451 patients who had cesarean sections during the study period, 223 were included" Comment: it appears that the 223 participants described as included were all included in the analyses but it's not completely clear that this is the total number who were randomised.
Selective reporting (reporting bias)	High risk	Comment: not all data relating to outcomes of infection, adverse events and postoperative hospitalisations were reported.
Other bias	Unclear risk	Comment: no obvious source of additional bias but reporting insufficient to be certain

Methods	Parallel‐group RCT Setting: 16 referral centres in the USA Follow‐up: 28‐56 d
Participants	449 women (age 32.6 years in Adept group vs 32.3 in lactated Ringer's solution group) undergoing laparoscopic gynaecological surgery. Primary diagnoses included pelvic pain, infertility endometriosis and known adhesions. Inclusion criteria: aged > 18 years and in good health. Laparoscopic surgery was planned for a gynaecologic procedure that included adhesiolysis followed by a second follow‐up laparoscopy 4–8 weeks later. Exclusion criteria: preoperative: the use of concomitant systemic corticosteroids, antineoplastic agents, and/or radiation; pregnancy; diagnosis of an active pelvic or abdominal infection, or cancer; and a known allergy to starch‐based polymers. Intraoperative exclusion criteria included women requiring an additional non obstetric/gynaecologic surgical procedure to be performed during the laparoscopic procedure; unplanned surgery necessitating opening the bowel (excluding appendectomy); any laparotomy procedure; and use of another adhesion reduction agent. Adhesion site exclusion criteria included women having < 3 of the available anatomical study sites with adhesions or, if fewer than three were lysed, removal of any anatomical sites being scored for the purposes of the study; and an inability to visualise clearly all available anatomical score sites.
Interventions	Group I: irrigated with a minimum 100 mL Adept (icodextrin 4% solution) solution every 30 min during surgery; any remaining solution at end of surgery was aspirated and then 1 L instilled from a fresh supply of solution (227 ITT, 205 PP participants) Group II: irrigated with a minimum 100 mL lactated Ringer's solution every 30 min during surgery; any remaining solution at end of surgery was aspirated and then 1 L instilled from a fresh supply of solution (222 ITT 205 PP participants)
Outcomes	Postoperative infections were reported but unclear whether these referred to SSI Group I (icodextrin): 1% of 227 calculated as 2  Group II (Ringer's solution): 3% of 222 calculated as 7 Secondary outcome: adverse events Group I (icodextrin): 221/227 of which 44 serious; 55 considered related, reported as serious 8 participants (25 events) Group II (Ringer's solution): 218/222 of which 36 serious; 38 considered related, reported as serious 11 participants (19 events) Secondary outcome: mortality Group I (icodextrin): 0/227 Group II (Ringer's solution): 0/222
Notes	Funding: Innovata Limited, Vectura Group
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Treatment was randomized by computer‐generated randomization on a 1:1 basis" Comment: an appropriate method of generating the randomisation sequence was reported.
Allocation concealment (selection bias)	Low risk	Quote: "Patient numbers were allocated to treatment group before labelling of the blinded study treatment  bags. The study solutions were presented in identical 1 L infusion bags, and each bag had an outer wrap that contained  the study code and patient number on an identification label" Comment: adequate method for concealment of treatment allocation reported
Blinding of participants and personnel (performance bias)   All outcomes	Low risk	Quote: "Double‐blinding was possible because Adept and LRS are both clear and odourless solutions  with similar viscosities to water." Comment: blinding appears to have been undertaken for personnel and participants.
Blinding of outcome assessment (detection bias)   All outcomes	Low risk	Quote: "Safety was assessed by serious adverse events (SAEs), adverse events, and changes in laboratory values. Patients completed  diary cards between initial surgery and follow‐up surgery. At postoperative checkup (visits 3 and 4), cards  were assessed to monitor progress. They allowed the patient to record their well‐being and all concomitant medications.  All adverse events whether they were considered related to study solutions or not, were investigated, and the details of  nature, severity, duration, outcome, and relationship to study device were recorded" Comment: safety outcomes were assessed by participants who were blinded to treatment allocation.
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Quote: "Safety was assessed in the intent‐to‐treat (ITT) population, which included all patients who had the study solution instilled.  Efficacy results are presented for the per protocol (PP) population. These patients were those who had completed both first‐ and second‐look laparoscopies without major protocol violations." Comment: the outcomes relevant to this review were assessed using the ITT population so almost all randomised participants were included in the analyses.
Selective reporting (reporting bias)	Low risk	Comment: outcomes were prespecified; all planned outcomes appeared fully reported.
Other bias	Low risk	Comment: no evidence of other sources of bias and reporting is sufficient to be reasonably confident that this is the case

Methods	Parallel‐group RCT Setting: appears to be single hospital in USA Follow‐up: 4‐6 weeks postoperatively
Participants	40 women undergoing caesarean section at high risk of infection
Interventions	Group I: irrigation with cefazolin; 2 g in 1000 cc normal saline; 700 cc intrauterine 100 cc in each gutter and 100 cc subcutaneously (20 participants) Group II: irrigation with 1000 cc normal saline 700 cc; intrauterine 100 cc in each gutter and 100 cc subcutaneously (20 participants) Cointerventions: none reported
Outcomes	Primary outcome: SSI (defined only as "wound infection") Group I (cefazolin): 1/20 Group II (saline): 1/20
Notes	Abstract only. Funding NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients at high risk of infection were randomly placed in two groups" Comment: no information as to how the randomisation sequence was generated
Allocation concealment (selection bias)	Unclear risk	Quote: "Patients at high risk of infection were randomly placed in two groups" Comment: no information as to whether there was adequate concealment of allocation
Blinding of participants and personnel (performance bias)   All outcomes	Unclear risk	Comment: no specific quote, no information as to whether these groups were blinded to treatment allocation
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Comment: there is no information as to who performed the outcome evaluation or whether they were blinded to treatment allocation
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Quote: "Only 2 of 40 high risk patients who received prophylactic irrigation developed...." Comment: it appears that all randomised participants were included in the analysis.
Selective reporting (reporting bias)	Unclear risk	Quote: "The objective of this study is to determine the impact of copious antibiotic irrigation versus normal saline (ns) on the incidence of post‐cesarean wound infections" Comment: the primary outcome was specified and reported but it is not clear from the abstract which other outcomes the study may have planned to assess.
Other bias	Unclear risk	Comment: there were no additional sources of bias noted but the abstract reporting was insufficient to be certain.

Methods	2‐arm RCT Setting: single centre, Emergency Department in Mexico Follow‐up: 2 and 4 weeks after operation
Participants	350 participants entered into study; 283 considered evaluable (mean age of 27.99 years (SD 12.81 years), range from 9‐82 years); (67 rejected from final analysis due to finding of another pathology different from appendix) Inclusion criteria: adults and children of both sexes admitted with a clinical diagnosis of acute abdomen suggestive of acute appendicitis with aid of laboratory and X‐ray, confirmed during operation and by histopathologic study Exclusion criteria: age < 5 years, allergy to metronidazole or aminoglycosides, antibiotic therapy within 72 h preceding operation, pregnancy, those with other intraperitoneal bacterial infection not originating from the appendix, and those with any immune deficiency (diabetes mellitus, chronic renal insufficiency, malnourishment, chemotherapy, radiotherapy, corticosteroid therapy, asplenism)
Interventions	Group I: no irrigation (156 participants) Group II: syringe pressure irrigation with saline: after closure of the fascial planes, subcutaneous fat tissue irrigated with 300 mL of normal saline solution, delivered with a 20‐mL syringe with a 19‐gauge IV catheter, applying to the embolus the force of one hand, at a distance of 2 cm from the wound tissues, aspirating the fluid collected in the wound with a bulb syringe (127 participants) Cointerventions: each participant was administered metronidazole (30 mg/kg/day) 3/d, plus amikacin (15 mg/kg/d) once daily IV 30–45 min before skin incision. In cases of uncomplicated appendicitis they were stopped within the first 24 h, whereas in cases of complicated appendicitis they were maintained for a minimum of 7 d
Outcomes	Primary outcome: SSI (Definition: "A wound was considered to be infected...when there was a collection of pus or a positive bacteriologic culture from a wound discharge") Group I: (no irrigation): 39/156 Group II: (syringe pressure irrigation): 11/127 Secondary outcome: adverse events. The authors stated that "Antibiotics used for prophylaxis were well tolerated without any case of allergy or intolerance." The proportion of participants with any adverse event was not reported.
Notes	Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "All patients included were randomly assigned by a computerized assignment system into 2 groups of the trial." Comment: randomisation sequence generated by computer
Allocation concealment (selection bias)	Low risk	Quote: "The randomization chart was kept by our statistician, who was blind to the follow‐up, until June 1995." Comment: appears that allocation sequence was concealed from trial personnel
Blinding of participants and personnel (performance bias)   All outcomes	High risk	Quote: "Statistical analysis of the results...was conducted by our statistician who was blind to the surgical procedures and follow‐up." Comment: control arm did not include comparator intervention and so unable to conceal allocation to staff present at operation. Study design indicated as "double blind," so assumption that participants were not told of their treatment allocation High risk of physicians not being blinded; unclear or low risk for participants
Blinding of outcome assessment (detection bias)   All outcomes	Low risk	Quote: "...sought by daily examination of all patients by one of the members of the research team who was blind to the random allocation and the surgical procedures, until discharge." Quote: "...reevaluated at the outpatient consultation 2 and 4 weeks after operation by the responsible author who was blind to the random assignment and the surgical procedures." Comment: appears that outcome assessment for SSI was conducted by blinded assessor
Incomplete outcome data (attrition bias)   All outcomes	High risk	Quote: "A total of 350 patients were entered into the study, and 283 (80.9%) were considered evaluable. The reason for rejection of the 67 (19.1%) patients from the final analysis was the finding of another pathology different from the appendix." Comment: the number of exclusions was high and the study did not achieve its aim of including 133 participants in each arm. Therefore confirmation of appendicitis during surgery appears to be an inclusion criterion and so exclusions based on pathology do not violate inclusion criteria. There was a high rate of exclusion relative to event rate for the primary outcome.
Selective reporting (reporting bias)	Unclear risk	Comment: main end point (defined surgical wound infection) was reported overall and for complicated and uncomplicated types of appendicitis. It is unclear whether there were any other end points specified in the study protocol.
Other bias	Unclear risk	Comment: there was no evidence of other sources of bias but reporting was insufficient to be certain.

Methods	2‐arm RCT Setting: single centre at hospital in Taiwan Follow‐up: at 2 weeks, 1 month and 3 months after operation, and then every 3 months until end of study (approximately 19 months)
Participants	244 participants (age range 20‐89 years; Group I: average 67.1 years, (range 20‐82 years); Group II: average 65.4 years (range 22‐89 years)). Inclusion criteria: primary instrumented lumbosacral posterolateral fusion for degenerative spinal disorder with lumbar or lumbosacral segmental instability defined by chronic back, buttock and/or leg pain and degenerative spondylolisthesis, degenerative scoliosis or isthmic spondylolisthesis Exclusion criteria: prior spinal surgery, spinal trauma, malignant tumour, infectious spondylitis, rheumatoid arthritis, ankylosing spondylitis, metabolic bone disease, skeletal immaturity or immunosuppressive treatment
Interventions	Group I (povidone‐iodine): wounds irrigated with 0.35% povidone‐iodine solution to soak for 3 min, followed by irrigation with 2000 cc normal saline to remove povidone‐iodine solution (120 participants) Group II (saline): wounds irrigated with only 2000 cc normal saline (124 participants) Cointerventions: wound closure by layer after suction drainage applied; drain removed 48 h or 72 h post‐operatively. Routine analgesic pain control applied for 3 d. Pre‐operative IV bolus injection of cefazolin (1000 mg) and gentamicin (60 mg); additional cefazolin (1000 mg/6 h) and gentamicin (60 mg/12 h) also given for 48 hs after surgery, and then oral cefazolin (500 mg/6 h) for 3 d
Outcomes	Primary outcome: SSI (Definition: "Infections were classified as superficial (above lumbosacral fascia) or deep (below lumbosacral fascia), and as early onset (within 2 weeks postoperatively) or late onset (otherwise). All deep infections were confirmed by laboratory parameters including erythrocyte sedimentation rate (ESR) and level of C‐reactive protein (CRP) and a positive culture of biopsy." Group I (povidone‐iodine): 0/120 Group II (saline): 6/124 (2 early onset; 4 late onset) Primary outcome: wound dehiscence within 30 d (time NR but it says all others healed with sutures removed on day 14 so can presume < 30 d. No infection found in wounds) Group I: 1/120 Group II: 2/124 Secondary outcome: proportion of participants with postoperative SSI using systemic antibiotics within 30 d of surgery Group II: (saline): "After radical debridement and parenteral antibiotics (according to sensitivities) for 6 weeks and oral antibiotics for 2 months, a satisfactory outcome has been reached except in two cases." Secondary outcome: occurrence of infections showing antibiotic resistance Group II: (saline): MRSA cultured from 5/6 cases Secondary outcome: surgical re‐intervention rates Group I: (povidone‐iodine): 3 participants underwent exploration of the non‐union site and re‐arthrodesis with autogenous bone graft Group II: (saline): 4 participants underwent exploration of the non‐union site and re‐arthrodesis with autogenous bone graft Group II: (saline): "After radical debridement and parenteral antibiotics (according to sensitivities) for 6 weeks and oral antibiotics for 2 months, a satisfactory outcome has been reached except in two cases." These 2 cases had implants removed 4 months post‐operatively as infection could not be eradicated
Notes	Interventions: no information given on duration of irrigation of wounds with normal saline for either group. Funding: Quote: "No funds were received in support of this work. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this manuscript."
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Patients...were randomly assigned to either treatment group. An independent person unaware of the subject characteristics and the study design delivered pre‐coded sealed enveloped randomly (containing serial numbers from 1 to 300) to the assignment of the subjects into the two groups." Comment: clearly states how sequence was generated
Allocation concealment (selection bias)	Unclear risk	Quote: "An independent person unaware of the subject characteristics an the study design delivered pre‐coded sealed enveloped randomly (containing serial numbers from 1 to 300) to the assignment of the subjects into the two groups. The sealed envelope was not opened until the middle of the surgery before wound irrigation." Comment: although sealed envelopes were used it is not clear that they were opaque or that the allocation sequence was fully concealed at all times.
Blinding of participants and personnel (performance bias)   All outcomes	Unclear risk	Comment: no direct quote, but no information on how personnel might have been blinded to the treatment performed. Unclear whether participants were blinded, but report states it was "single blind"
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Quote: "All clinical and radiographic assessments were made by independent observers other than the treating surgeons." Comment: unclear whether observers were aware of treatment group
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Comment: no direct quote, but no evidence of attrition
Selective reporting (reporting bias)	Unclear risk	Comment: no evidence of selective reporting but not enough information to be certain
Other bias	Unclear risk	Comment: there was no evidence of other sources of bias but reporting was insufficient to be certain

Methods	Parallel RCT Setting: single centre in Republic of Korea Follow‐up: 2 weeks
Participants	34 patients undergoing gastrectomy Inclusion criteria: naive stomach cancer patients Exclusion criteria: history of diabetes, pneumonia, urinary tract infection, chemotherapy
Interventions	Group I: saline exchange after gastrectomy (17 participants) Group II: no saline exchange during surgery (17 participants) Co‐interventions: preoperative cefametazol 1 g
Outcomes	Primary outcome: SSI Superficial, deep SSI defined by Horan 1992 Group I (saline exchange): 1/17 Group II (no saline exchange): 3/17
Notes	Funding: NR Reported in Korean. Data extraction and risk of bias assessment performed by translator
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Comment: random number table was used
Allocation concealment (selection bias)	Unclear risk	Comment: method of allocation concealment was not described
Blinding of participants and personnel (performance bias)   All outcomes	High risk	Comment: personnel were blinded because they were under anaesthesia but personnel would have been aware of the allocation due to the nature of the comparison
Blinding of outcome assessment (detection bias)   All outcomes	Low risk	Comment: outcome assessors were blinded
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Comment: all participants were included
Selective reporting (reporting bias)	Low risk	Comment: pre‐specified outcomes were reported
Other bias	Low risk	Comment: not detected

Methods	Parallel‐group, 5‐arm RCT Setting: single hospital in USA Follow‐up: unclear
Participants	360 women undergoing caesarean section. Both caesareans in labour and without labour were included. Mean ages between 24.59 and 27.52 years. Gestational ages between 37.85 and 39.31 weeks Inclusion criteria: women undergoing caesarean section Exclusion criteria: history of penicillin or cephalosporin allergy, taking antibiotics, known infectious process (e.g. chorioamnionitis or urinary tract infection)
Interventions	Group 1: saline lavage (800 mL) Group 2: 2 g cephapirin sodium lavage Group 3: 2 g cefamandole nafate lavage Group 4: 2 g moxalactam disodium lavage Group 5: 2 g ampicillin sodium lavage Inferred that each antibiotic lavage used 800 mL Cointerventions: none reported
Outcomes	Primary outcome: SSI (wound breakdown with positive culture or presence of cellulitis) Group 1 (saline): 3/77 Group 2 (cephapirin): 3/70 Group 3 (cefamandole): 2/64 Group 4 (moxalactam): 2/79 Group 5 (ampicillin): 0/70 Secondary outcome: adverse events including abscess There were 0 abscess events; other adverse events reported were infection‐related morbidity as follows Group 1 (saline): 22/77 Group 2 (cephapirin): 17/70 Group 3 (cefamandole): 8/64 Group 4 (moxalactam): 19/79 Group 5 (ampicillin): 10/70
Notes	Funding NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "A computer‐generated table of pseudo‐random numbers.... was used by the pharmacy to assign each patient to one of five groups" Comment: an acceptable method of sequence generation was reported.
Allocation concealment (selection bias)	Unclear risk	Quote: "A computer‐generated table of pseudo‐random numbers.... was used by the pharmacy to assign each patient to one of five groups" Comment: there was no information on how allocation concealment was undertaken.
Blinding of participants and personnel (performance bias)   All outcomes	Low risk	Quote: "A vitamin .... was added to each solution for disguise" "The patients and physicians were unaware of the group assignment until after completion of the study and chart review by the authors" Comment: blinding of both participants and physicians was undertaken.
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Comment: no specific quote but it was unclear who performed the outcome assessments and hence whether they were blinded to group allocation.
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Comment: all randomised participants were included in the analyses.
Selective reporting (reporting bias)	Unclear risk	Comment: the outcomes were not defined in the methods section so it is unclear whether all planned outcomes were fully reported.
Other bias	Unclear risk	Comment: no apparent sources of additional bias but reporting insufficient to be certain

Methods	2‐arm RCT with 2 phases Setting: NR, but appears to be a general surgery department at a hospital in the Netherlands Follow‐up: at 4, 8 and 14 d, and 4 weeks after surgery
Participants	592 participants, of which 34 excluded (18 in the control group and 16 in the povidone‐iodine group) because they died before the end of the control period or had to be operated upon again through the same wound during this period. 2 wounds were present in 21 participants (9 in the control group and 12 in the povidone‐iodine group). A total of 582 wounds were evaluated in 558 participants. Inclusion criteria: all elective and acute patients who underwent intra‐abdominal operations or operations for inguinal hernia Exclusion criteria: children < five years of age and those undergoing vascular reconstruction.
Interventions	Group I (control): quote "No special measures were taken" Group II (povidone‐iodine): carried out in 2 phases. Subcutaneous tissues irrigated with a povidone‐iodine solution at the end of the operation. Lavage with an ample amount of 1% aqueous povidone‐iodine solution (Phase 1) or 10% aqueous povidone‐iodine solution (Phase 2). Lavage was performed after closure of the fascia with interrupted polyglactin 910 sutures. After lavage for 1 min, excess fluid was aspirated and skin closed with interrupted with nylon sutures. If present, drains were brought out through a second wound.
Outcomes	Primary outcome: SSI (Definition: "Diagnosis of wound infection made if a purulent discharge form the wound was seen within a period of four weeks after the operation or if culturing of fluid from the wound was positive.") Group I (control): Phase 1: 21/142 wounds Phase 2: 15/137 wounds (270 participants? ‐ participant numbers unclear) Group II (povidone‐iodine): Phase 1: 17/154 wounds Phase 2: 22/149 wounds (291 participants? ‐ participant numbers unclear)
Notes	Participants: age NR Outcomes: these appear to refer to number of wounds, not participants Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The patients were divided at random into two groups." Comment: it is unclear how randomisation was performed.
Allocation concealment (selection bias)	Unclear risk	Quote: "The patients were divided at random into two groups." Comment: no information on whether the randomisation sequence was concealed
Blinding of participants and personnel (performance bias)   All outcomes	High risk	Quote: "In the first group, no special measures were taken." Comment: the control arm did not involve an intervention as a comparator, and so unable to conceal allocation to staff present at the operation. Unclear whether all staff were aware of the different phases of the study (and concentrations of solution used as the intervention). Unclear whether participants were aware of treatment allocation
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Quote: "Postoperatively, all wounds were assessed by the same investigator..." Comment: unclear as to whether the investigator was blinded to the treatment allocation
Incomplete outcome data (attrition bias)   All outcomes	High risk	Quote: "34, 18 in the control group and 16 in the povidone‐iodine group, were excluded because they either died before the end of the control period or had to be operated upon again through the same wound during this period." Comment: number of exclusions is high. No reasons given for cause of death or re‐operations
Selective reporting (reporting bias)	Unclear risk	No evidence of reporting bias, but report is not complete enough to be sure
Other bias	Unclear risk	Comment: there was no evidence of other sources of bias but reporting was not clear enough to be certain

Methods	4‐arm RCT Setting: 2 hospitals in USA Follow‐up: 6 weeks
Participants	'High risk' patients (for developing post operative febrile morbidity) undergoing cesarean section for a variety of reasons 158 women included in study Inclusion criteria: women in active labour or with ruptured membranes, at least one digital vaginal examination (i.e. high risk from developing postoperative febrile morbidity) Exclusion criteria: allergy to cephalosporins or penicillin, presence of fever ≥ 37.8 C during labour with suspicion of chorioamnionitis, maternal use of antibiotics in 2‐week period before delivery
Interventions	Group I: 8 doses of IV cefoxitin 2 g (1st dose after umbilical cord clamp, then every 6 hs) (39 participants) Group II: irrigation of uterus and peritoneum with 2 g cefoxitin (in 1000 mL of normal saline). After delivery of the placenta, the fundus of the uterus was irrigated with 300 mL, the uterine incision with 150 mL, after closure of the first layer 150 mL, bladder flap 150 mL, remainder used to irrigate peritoneal cavity and excess suctioned away before closure of the abdomen (42 participants) Group III: combination of IV antibiotic (8 doses of 2 g cefoxitin) and irrigation with cefoxitin (in 1000 mL of normal saline) i.e. treatments of groups I and II combined (38 participants) Group IV: control group who received no prophylactic antibiotics (39 participants)
Outcomes	Primary outcome: SSI (wound infection) Group I (IV antibiotics only): 0/39 Group II (irrigation with antibiotics only): 0/42 Group III (IV antibiotics plus irrigation with antibiotics): 0/38 Group IV (no IV and no irrigation):1/39 Secondary outcome: hospital stay (mean (SD) d) Group I: 4.8 (1.1) Group II: 4.9 (1.0) Group III 4.9 (1.2) Group IV: 5.4 (1.4) Secondary outcome: adverse events Infectious (endomyometritis, urinary tract infection, wound infection (1 case, see above), pulmonary infection, septicaemia) Group I: 2/39 Group II: 3/42 Group III: 2/38 Group IV: 14/39 Non‐infectious (seroma, transfusion reaction, atelectasis) Group I: 1/39 Group II: 1/42 Group III: 1/38 Group IV: 0/39
Notes	Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Randomization into one of four treatment groups was performed by using a table of random numbers" Comment: an appropriate method appears to have been used
Allocation concealment (selection bias)	Unclear risk	Comment: there is no information about allocation concealment
Blinding of participants and personnel (performance bias)   All outcomes	High risk	Comment: there is no information about blinding. It is possible that participants were blinded, but personnel would be aware of treatment as the protocols are quite different.
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Comment: there is no information about blinding or who performed outcome assessment
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Comment: all participants are accounted for in the results
Selective reporting (reporting bias)	Unclear risk	Comment: the outcomes do not appear to have been pre‐specified, although febrile morbidity was extensively defined
Other bias	Unclear risk	Comment: there is no evidence of additional sources of bias but the reporting is insufficient to be confident that there were none.

PERMALINK

Intracavity lavage and wound irrigation for prevention of surgical site infection

Gill Norman

Ross A Atkinson

Tanya A Smith

Ceri Rowlands

Amber D Rithalia

Emma J Crosbie

Jo C Dumville

Abstract

Background

Objectives

Search methods

Selection criteria

Data collection and analysis

Main results

Authors' conclusions

Plain language summary

Summary of findings

Background

Description of the condition

Description of the intervention

How the intervention might work

Why it is important to do this review

Objectives

Methods

Criteria for considering studies for this review

Types of studies

Types of participants

Types of interventions

Types of outcome measures

Primary outcomes

Secondary outcomes

Search methods for identification of studies

Electronic searches

Searching other resources

Data collection and analysis

Selection of studies

1.

Data extraction and management

Assessment of risk of bias in included studies

2.

3.

Measures of treatment effect

Unit of analysis issues

Dealing with missing data

Assessment of heterogeneity

Assessment of reporting biases

Data synthesis

'Summary of findings' tables

1. Summary of GRADE assessments for comparisons with limited data.

Subgroup analysis and investigation of heterogeneity

Sensitivity analysis

Results

Description of studies

Results of the search

Included studies

Ongoing or pending assessment studies

Excluded studies

Risk of bias in included studies

Allocation

Blinding

Incomplete outcome data

Selective reporting

Other potential sources of bias

Effects of interventions

Summary of findings for the main comparison. All irrigation compared with no irrigation for prevention of surgical site infection.

Summary of findings 2. Irrigation with antibacterial solution compared with irrigation with non‐antibacterial solution for prevention of surgical site infection.

Summary of findings 3. Standard irrigation compared with pulsatile irrigation for prevention of surgical site infection.

Comparison 1: comparison of irrigation with no irrigation

Primary outcome: SSI

2. Summary of primary outcome data: surgical site infection (SSI) and wound dehiscence.

1.1. Analysis.

4.

3. Summary of subgroup analyses.

Primary outcome: wound dehiscence

Secondary outcome: adverse events

1.2. Analysis.

1.3. Analysis.

Secondary outcome: mortality

Methods	2‐arm RCT Setting: single hospital in UK Follow‐up: 1 month
Participants	129 patients undergoing elective and emergency colorectal surgery Age: unknown; Type of operations: unknown Inclusion criteria: NR Exclusion criteria: NR
Interventions	Group I: 1000 mL saline lavage at the end of the operation (65 participants) Group II: 1000 mL saline lavage with 1 g cefotetan at the end of the operation (64 participants) Co‐interventions: Groups I and II both received 500 mg metronidazole and 120 mg gentamicin IV at anaesthesia induction
Outcomes	Primary outcome: SSI (defined as discharge of pus from the wound "wound sepsis") Group I (saline): 18/65 Group II (cefotetan): 15/64
Notes	Funding: NR Limited information from paper
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients were randomly allocated to receive either 1 liter of saline lavage or 1 liter of saline containing 1g of cefotetan..." Comment: the method of randomisation is not described
Allocation concealment (selection bias)	Unclear risk	Comment: there is no mention of allocation concealment
Blinding of participants and personnel (performance bias)   All outcomes	Unclear risk	Comment: there is no mention of blinding of participants or personnel
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Quote: "Post‐operatively, patients were assessed regularly by a single observer for the development of wound sepsis..." Comment: there is no mention of blinding of the observer
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Comment: participants are all accounted for in the outcome data of interest
Selective reporting (reporting bias)	Unclear risk	Comment: the outcome of interest (SSI) is reported but it is not clear that related results are fully reported
Other bias	Unclear risk	Comment: there is not enough methodological information to judge whether there were any additional sources of bias

Methods	2‐arm RCT Setting: single hospital in Turkey Follow‐up: participants were examined at 2 and 6 weeks after surgery. Wounds examined twice daily during hospitalisation. After discharge, women were instructed to contact investigators immediately if any of the listed symptoms appeared. Women who contacted the investigators were examined within 12 h
Participants	520 women with indications for elective or emergency caesarean section (incidence of emergency surgery (45.5 vs 51.5%; P = 0.53)) Inclusion criteria: past 37 weeks' gestation and required a caesarean section (elective or emergency). Exclusion criteria: anaemia (haemoglobin: < 7 g/dL), chorioamnionitis and fever on admission
Interventions	Group I: underwent wound irrigation before wound closure with 100 mL of sterile saline with a 30–60 mL syringe (260 participants) Group II: no wound irrigation before wound closure (260 participants)
Outcomes	Primary outcomes: SSI (wound drained purulent material or serosanguineous fluid in association with induration, warmth and tenderness) Group I (saline): 17/260 Group II (no irrigation): 19/260 Secondary outcomes: mean length of hospital stay Group I (saline): 2.05 (0.21) d Group II (no irrigation): 2.04 ( 0.20)
Notes	Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Consenting patients were preoperatively randomised using numerically ordered cards in sealed envelopes" Comment: method of sequence generation is not reported
Allocation concealment (selection bias)	Unclear risk	Quotes: "Consenting patients were preoperatively randomised using numerically ordered cards in sealed envelopes" "The investigator was not blinded to the procedure allocation" "The allocated envelope was opened by the clinician just before surgery" Comment: the use of sealed envelopes suggests an attempt to conceal some aspect of allocation but the authors state that the investigator was not blinded to allocation; envelopes are not stated to be opaque
Blinding of participants and personnel (performance bias)   All outcomes	High risk	Quote: "The allocated envelope was opened by the clinician just before surgery. The procedure allocation was recorded in the women's charts" Comment: personnel and participants were both aware of treatment
Blinding of outcome assessment (detection bias)   All outcomes	High risk	Quote: "The procedure allocation was recorded in the women's charts" "The investigator was not blinded to the procedure allocation" Comment: it is not explicitly stated but the report suggests the outcome assessors were not blinded
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Comment: data are reported for all participants
Selective reporting (reporting bias)	Unclear risk	Comment: apart from SSI, it is unclear which outcomes were prespecified
Other bias	Low risk	Comment: there is no evidence of other bias

Methods	2‐arm RCT Setting: multicentre trial: 4 UK hospitals in the "South of England" Study period: 18‐months Follow‐up: 30 d post surgery or discharge from unit (1 assessor in each hospital reviewed participants' wounds twice a week until discharge)
Participants	356 participants with a displaced intracapsular fractured neck of femur, due to be treated with a hemiarthroplasty, were randomised into 2 groups Inclusion criteria: displaced intracapsular fractured neck of femur, due to be treated with a hemiarthroplasty Exclusion criteria: NR
Interventions	Group I: the ‘pulse lavage’ group had a 2‐L normal saline wash delivered via pulsatile lavage in stages throughout the procedure (164 participants) Group II: the control group had a 2‐L normal saline wash delivered by a jug or a syringe according to the surgeon's preference with 1 L being given before prosthesis insertion and 1 L after insertion (192 participants) Co‐interventions: NR
Outcomes	Primary outcome: SSI Wound infections were diagnosed using criteria from the Nosocomial Infection National Surveillance Survey and graded as superficial or deep. Group I (pulse lavage): 9/164 (3/164 'deep') Group II (control): 30/192 (10/192 'deep') Secondary outcome: occurrence of infections with antibiotic resistance No group data but quote: "Half of the deep space infections were due to methicillin‐resistant Staphylococcus aureus" Secondary outcome: mortality NR by group. There were 25 deaths within the study period (7%); 18 of these were associated with American Society of Anaesthesiologists (ASA) scores of 3 or below
Notes	Funding: no records
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "...all patients... were randomized into two groups" Comment: no details about method
Allocation concealment (selection bias)	Unclear risk	Comment: no mention of allocation concealment
Blinding of participants and personnel (performance bias)   All outcomes	High risk	Comment: no mention of blinding, but nature of intervention and control means personnel would not be blind to treatment
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Quote: "One assessor in each hospital reviewed patients' wounds twice a week until discharge" Comment: no mention of blinding and it is unclear if the assessor would have been aware of treatment
Incomplete outcome data (attrition bias)   All outcomes	High risk	Quote: "the difference in size between the two groups was due to 'start up' problems within the hospitals where pulse lavage had not been previously associated with hemiarthroplasty operations" "In cases where hemiarthroplasties were due to have pulse lavage but this was forgotten, the cases were struck from the study" Comment: the authors describe issues with implementing the pulse lavage intervention and although they describe participants being excluded at some point for this reason (presumably post‐randomisation) there are no details about them. It is probable that this introduced bias to the study.
Selective reporting (reporting bias)	High risk	Comment: data are fully reported for some outcomes but others are not reported by group
Other bias	Unclear risk	Comment: there is insufficient information to judge

Methods	2‐arm, parallel‐group RCT Setting: single centre in USA Follow‐up: NR
Participants	196 women undergoing caesarean delivery. 94 were elective repeat procedures, age 27.5 vs 28.2 years Inclusion criteria: women presenting with term (> 37 weeks) singleton pregnancies undergoing routine caesarean delivery for arrest of dilation, arrest of descent, foetal malpresentation or as an elective repeat procedure Exclusion criteria: women diagnosed with chorioamnionitis, type I diabetes, placenta previa, placenta accreta, maternal coagulopathy, multiple gestation, HIV–positive status, prior severe gastrointestinal disease, or non‐reassuring fetal monitoring requiring immediate delivery
Interventions	Group I: irrigation with 500‐1000 mL warm saline after closure of the uterine incision but before closure of the abdominal wall (97 participants) Group II: no irrigation (99 participants)
Outcomes	Primary outcome: SSI (undue tenderness, erythema, discharge, or separation of the incision accompanying maternal fever) Group I (saline irrigation): 1/97 Group II (no irrigation): 2/99 Secondary outcome: length of stay (d) Group I (saline irrigation): 2.9 (1.0) Group II (no irrigation): 2.8 (0.9) Secondary outcome: adverse events (postpartum complications including SSI) Group I (saline irrigation): 14/97 Group II (no irrigation): 13/99
Notes	Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Assignment was performed by pulling sequentially numbered opaque envelopes containing computer‐randomized individual allocations." Comment: an appropriate method of random sequence generation was reported
Allocation concealment (selection bias)	Low risk	Quote: "Assignment was performed by pulling sequentially numbered opaque envelopes containing computer‐randomized individual allocations." Comment: an appropriate method of allocation concealment was reported
Blinding of participants and personnel (performance bias)   All outcomes	High risk	Quote: "This randomization was carried out by research staff before initiation of the study, and the patients were blinded to treatment once assigned." Comment: although participants were blinded to treatment allocation it is unclear whether personnel were also blinded, the nature of the intervention groups suggests that they were not.
Blinding of outcome assessment (detection bias)   All outcomes	Low risk	Quote: "Postoperative care providers were blinded to group assignment to minimize potential bias. .... The randomizing physician collected the initial data. Data entry was performed by data technicians who did not participate in the design or execution of the study; these technicians also reviewed the charts of each randomized patient to assess the accuracy of information provided by the treating physician. The senior investigator performed periodic reviews of data entry to ensure completeness and accuracy of information in the computer database. The data analysis was performed by an investigator blinded to group assignment." Comment: blinded outcome assessment was conducted
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Comment: all randomised participants were included in the analyses
Selective reporting (reporting bias)	Low risk	Quote: "The primary outcome measure was the incidence of maternal morbidity, defined as the presence of at least one of the following:..." Comment: primary and secondary outcomes were clearly specified and fully reported.
Other bias	Low risk	Comment: there were no other sources of bias evident and reporting was sufficient to be reasonably confident that this was the case.

Methods	2‐arm RCT Setting: single hospital in Slovakia Follow‐up: 7.8 months (mean) 2‐14 months (range): follow‐up at 2 weeks, 6 weeks and then 3‐monthly
Participants	162 children (undergoing 182 surgical procedures on soft and bone tissues in the proximal femur, hip and pelvic regions. mean age was 7.9 vs 7.5 years Types of procedures: adductor tenotomy, femoral or pelvic osteotomy, extraction of metal materials, open reductions, epiphysiodesis, resection or biopsy. Children had the following long‐term conditions: developmental dysplasia of the hip, cerebral palsy, tumours, Perthes disease Inclusion criteria: children undergoing surgery of the femur, hip or pelvis Exclusion criteria: NR
Interventions	Group I: lavage with 3.5% Betadine solution (0.35% povidone iodine) diluted in 30 mL sterile saline Group II: lavage with 30 mL sterile saline Cointerventions: antibiotic prophylaxis begun preoperatively in participants with femoral or pelvic osteotomy or massive surgery of soft tissues and continued for 48‐72 hs postoperatively (dose determined by weight). Drains left in until second postoperative day where necessary
Outcomes	Primary outcome: SSI (positive bacteriological examination) Group I (Betadine lavage): 0/89 Group II (saline lavage): 2/73
Notes	Funding: NR Slovak; data entry and risk of bias based on information provided by translator
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Comment: no information about the sequence generation process but stated that the participants were allocated to 2 groups randomly
Allocation concealment (selection bias)	Unclear risk	Comment: no information on whether the allocation was adequately concealed
Blinding of participants and personnel (performance bias)   All outcomes	Unclear risk	Comment: no information on whether personnel or participants were blinded to the interventions
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Comment: no information on who assessed the presence of SSI or whether they were blinded to treatment allocation
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Quote "In the first group (89 patients) [we] found no peri‐ or post‐operative infection. In the second group of patients (73) [we] brought to light two surface infection[s] (2.7%)" Comment: it appears that all participants were included in the analysis
Selective reporting (reporting bias)	Unclear risk	Comment: outcomes were not specified in the methods section so difficult to be certain whether all planned outcomes were assessed
Other bias	Unclear risk	No evidence of additional bias but reporting insufficient to be certain

Methods	2‐arm RCT Setting: NR, appears to be single centre in Japan Follow‐up: NR
Participants	16 children (aged 2‐12 years) undergoing appendectomy for perforated appendicitis Inclusion criteria: generalised peritonitis or nonlocalised abscess Exclusion criteria: NR
Interventions	After appendectomy, the peritoneal cavity was lavaged with 100 mL/kg (1500‐4000 mL) of the following warmed lavage solutions: Group I : normal saline (8 participants) Group II: acidic oxidative water (AOPW), a strong acidic water produced by the electrolysis of tap water containing 10% W/V sodium chloride (8 participants) Co‐interventions: antibiotics moxalactam [reported as LMOX] (100 mg/kg/d) or cefazolin [reported as CEZ] (50 mg/kg/d) were given in both groups for 5 d or until serum C‐reactive protein was at a normal level
Outcomes	Primary outcome: SSI No definition given for wound infection Group I (saline): 4/8 Group II (APOW): 1/8 Secondary outcome: adverse events: abscess formation Group I (saline): 1/8 Group II (APOW): 0/8 Secondary outcome: length of hospital stay (mean (SD) d) Group IS (saline): 22.7 (11.1) Group II (APOW): 12.1 (5.1)
Notes	Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "They were randomly divided into two groups" Comment: no details of randomisation method
Allocation concealment (selection bias)	Unclear risk	Comment: no mention of allocation concealment
Blinding of participants and personnel (performance bias)   All outcomes	Unclear risk	Comment: no mention of blinding
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Comment: no mention of who performed the assessment of outcomes or whether blinding occurred
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Comment: all participants are included in the results
Selective reporting (reporting bias)	High risk	Comment: outcomes were not prespecified beyond "effectiveness and safety"
Other bias	Unclear risk	Comment: there is not enough methodological detail to judge

Methods	2‐arm RCT Setting: appears to be multiple centres, Japan ("our affiliated hospitals") Follow‐up: 30 d Duration of study: 2008‐2012
Participants	44 children aged 3‐14 Group I: 16 boys and 4 girls, ranging in age from 4‐11 years Group II: 12 boys and 12 girls, ranging in age from 3‐14 years Inclusion criteria: children (age not defined) appendectomy for perforated appendicitis with extensive or panperitonitis Exclusion criteria: pre‐operative antibiotics or requirement of antibiotics due to massive abscess formation
Interventions	After appendectomy, the peritoneal cavity was lavaged with 100 mL/kg saline or SAEW (strong acid electrolysed water, generated by electrolysis of tap water containing 0.2% NaCl), in Groups I and II, respectively. After closure of the fascial layer, the wound was washed out with 200 mL same solution before skin suture Group I: 100 mL/kg saline (20 participants) Group II: 100 mL/kg SAEW (24 participants) Co‐intervention: cefmetazole, 100 mg/kg/d, was given initially to both groups, which was replaced by the most sensitive antibiotics after identification of causative pathogens for 5 or 7 d depending on response. The abdominal wall was disinfected with povidone iodine, and laparotomy was performed via a pararectal incision, saving the muscle layers, followed by appendectomy, carried out in the same manner in both groups.
Outcomes	Primary outcome: SSI Defined as infection at the operation site, occurring up to 30 d after surgery, with confirmed causative pathogen(s) identical to those of the appendicitis. Group I (saline): 4/20 Group II (SAEW): 0/24 Secondary outcome: adverse events (intraperitoneal abscess) Group I (saline): 1/20 Group II (SAEW): 1/24 Secondary outcome: length of hospital stay (mean (SD) d) Group I (saline): 9.4 (4.7) Group II (SAEW): 8.7 (4.0)
Notes	34 participants were excluded from the study because some had received antibiotics before the operation and some had required antibiotics for massive abscess formation to be resected primarily with appendectomy Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients were allocated randomly to one of two treatment groups" Comment: no details about method of randomisation
Allocation concealment (selection bias)	Unclear risk	Comment: no mention of allocation concealment
Blinding of participants and personnel (performance bias)   All outcomes	Unclear risk	Comment: no mention of blinding
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Comment: no mention of who performed the outcome assessment or whether blinding occurred
Incomplete outcome data (attrition bias)   All outcomes	High risk	Quote: "34 patients were excluded from the study..." Comment: it is unclear if the exclusions were before or after randomisation
Selective reporting (reporting bias)	Low risk	Comment: all outcomes of interest appear to be reported
Other bias	Unclear risk	Comment: there is not enough methodological information to judge

Methods	3‐arm RCT Setting: Kaiser‐Permanente Medical Center ‐ Santa Clara, USA Follow‐up: at least 8 weeks
Participants	128 women undergoing cesarean section for various indications including repeat, breech and cephalopelvic disproportion. (132 entered study but 4 were excluded for irrigation protocol deviation and data are only presented for 128) Inclusion criteria: undergoing cesarean section Exclusion criteria: fever or other evidence of infection in labour, history of sensitivity to cephapirin or cefoxitin
Interventions	Group I: following delivery of the placenta, the uterine cavity and incision, bladder flap, pelvic gutters, and subcutaneous tissue were irrigated with 2 mg cephapirin in 1000 mL normal saline (44 participants) Group II: irrigation with 2 mg cefoxitin in 1000 mL normal saline (41 participants) Group III: irrigation with 1000 mL normal saline only (43 participants)
Outcomes	Primary outcome: SSI (defined as purulent wound discharge with or without wound separation) Group I (cephapirin): 0/44 Group II (cefoxin): 0/41 Group III (saline): 3/43 Secondary outcome: endometritis (defined as persistent fever, uterine tenderness, foul‐smelling lochia, with no other obvious source of infection) Group I (cephapirin):4/44 Group II (cefoxin): 1/41 Group III (saline): 5/43 (one of these also had wound infection) Secondary outcome: length of hospital stay (mean (SD) d) Group I (cephapirin): 4.8 (1.2) Group II (cefoxin): 4.9 (1.9) Group III (saline): 5.2 (2.1)
Notes	4 excluded from the analysis for protocol deviation Funding: NR
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "... bags were sequenced randomly by a lottery method and used in numerical order" Comment: the method is not explained in enough detail to know whether it was appropriate
Allocation concealment (selection bias)	Unclear risk	Quote: "... bags were sequenced randomly by a lottery method and used in numerical order" Comment: there is not enough detail about the method of randomisation and allocation concealment to judge
Blinding of participants and personnel (performance bias)   All outcomes	Low risk	Quote: "...bags of irrigant were prepared by pharmacy personnel" "One millilitre of multivitamin infusion was added to create an identical appearance of all solutions" "Patients, physicians, operating room personnel, and data collectors were thus blinded to the group assignment." Comment: steps were have been taken to ensure blinding of participants and personnel
Blinding of outcome assessment (detection bias)   All outcomes	Low risk	Quote: "Patients, physicians, operating room personnel, and data collectors were thus blinded to the group assignment." Comment: steps appear to have been taken to ensure blinding of outcome assessors
Incomplete outcome data (attrition bias)   All outcomes	Unclear risk	Quote: "One hundred thirty‐two patients were entered in the study. Four patients were eliminated from the statistical analysis because of deviations from the protocol of irrigation technique" Comment: there are only a few participants lost during the study but no details of these participants are reported and since numbers of events are small this could potentially have an impact.
Selective reporting (reporting bias)	Low risk	Comment: the outcomes of interest appear to be fully reported
Other bias	Low risk	Comment: there is no evidence of other bias

Methods	Parallel‐group RCT (factorial) Setting: single hospital in the USA Follow‐up: NR
Participants	100 women undergoing caesarean section Inclusion criteria: women undergoing caesarean section; indications for surgery included elective repeat caesarean, failed trial of labour after prior caesarean, abnormal presentation, failure to progress, cephalopelvic disproportion, and severe pre‐eclampsia without thrombocytopenia or coagulopathy  Exclusion criteria: chorioamnionitis at caesarean, emergency caesarean for foetal distress with inadequate time for skin preparation
Interventions	Group I: saline irrigation (500 mL) of pelvis and subcutaneous tissue at uterine and fascial closure (50 participants) Group II: cefazolin irrigation (1 g in 500 mL saline) of pelvis and subcutaneous tissue at uterine and fascial closure (50 participants) Cointerventions: factorial randomisation to 2 alternative skin preparations: povidone iodine 7.5% scrub followed by povidone iodine 10% solution (standard skin preparation) versus 5‐min scrub with parachlorometaxylenol followed by povidone iodine scrub and solution (special skin preparation). No additional interventions were reported.
Outcomes	Primary outcome: SSI (hyperemic skin incision and fluctuant mass which when opened contained purulent material) Group I (saline): 4/50 (3/25 with standard skin preparation; 1/25 with special skin preparation) Group II (cefazolin): 2/50 (2/25 with standard skin preparation) Secondary outcome: adverse events (endometritis) Group I (saline): 30/50 (16/25 with standard skin preparation; 14/25 with special skin preparation) Group II (cefazolin): 11/50 (8 with standard skin preparation; 3/25 with special skin preparation)
Notes	Funding: supported in part by the Vicksburg Hospital Medical Foundation
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Random assignment was achieved by card selection from sealed opaque envelopes with group appointment derived from a random number table" Comment: it appeared that an appropriate method was used to generate the randomisation sequence
Allocation concealment (selection bias)	Unclear risk	Quote: "Random assignment was achieved by card selection from sealed opaque envelopes with group appointment derived from a random number table" Comment: it was not clear that enough measures were taken to ensure adequate concealment of allocation
Blinding of participants and personnel (performance bias)   All outcomes	Unclear risk	Comment: there was no information on whether personnel and participants were blinded to treatment allocation
Blinding of outcome assessment (detection bias)   All outcomes	Unclear risk	Comment: there was no information on who performed the outcome assessment or whether they were blinded to treatment allocation
Incomplete outcome data (attrition bias)   All outcomes	Low risk	Comment: all randomised participants were included in the analyses
Selective reporting (reporting bias)	Unclear risk	Comment: outcomes were not clearly prespecified so difficult to determine if all planned outcomes were fully assessed
Other bias	Unclear risk	Comment: no obvious additional sources of bias but reporting insufficient to be certain

Methods	2‐arm RCT Setting: single hospital in Australia Follow‐up: letter or text message 4 weeks after surgery (following discharge from hospital)
Participants	3270 women undergoing caesarean section. Of those followed up 1508 had elective surgery and 1519 had surgery during labour. Mean age was 28.5 years in the Betadine group vs 28.6 years in the no Betadine group. 13.8% versus 12.9% had diabetes Inclusion criteria: women undergoing caesarean section either elective or during labour (stratified randomisation) Exclusion criteria: suspected or known allergy to iodine
Interventions	Group I: wound irrigation with 50 mL of 10% aqueous povidone iodine (Betadine) solution just before skin closure (1634 participants randomised; 1634 received allocated intervention; 1520 analysed) Group II: no irrigation (1636 participants randomised; 1636 received allocated intervention; 1507 analysed) Cointerventions: alcoholic povidone iodine for skin preparation unless an allergy to iodine present, in which case chlorhexidine was used. Prophylactic cephalothin administered to all women soon after spinal anaesthesia
Outcomes	Primary outcome: SSI (wound abscess or wound draining pus or sero‐sanguinous fluid, or redness, induration, warmth and tenderness or if woman’s general practitioner had seen her and prescribed antibiotics for presumed infection) Group I (povidone iodine irrigation): 144/1520 Group II (no irrigation): 147/1507 Secondary outcome: return to theatre Group I (povidone iodine irrigation): 7/1520 Group II (no irrigation): 9/1507 Secondary outcome: hospital readmission Group I (povidone iodine irrigation): 39/1520 Group II (no irrigation): 30/1507 Completed case analyses reported here: ITT population 1634 vs 1636 ‐ used in analyses for SSI
Notes	Funding: states "we had no funding for this study..."
*Risk of bias*
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The allocation was prepared using computer generated list of random numbers using a variable block of 10 and performed by a staff member not part of the clinical team" Comment: acceptable method of sequence generation; randomisation also stratified by elective versus non‐elective procedure
Allocation concealment (selection bias)	Low risk	Quote: "Women were randomised to ‘Betadine’ or ‘no Betadine’ group using sequentially numbered sealed opaque envelopes that contained the allocation..... After all layers were sutured and just prior to starting skin closure, the envelope with the allocation was opened by one of the theatre nurse[sic]" Comment: appropriate measures appear to have been taken to ensure allocation concealment.
Blinding of participants and personnel (performance bias)   All outcomes	High risk	Quote "In the control group (no Betadine group), layers would be sutured in exactly the same manner right up to the point of skin closure as it was only at this point that the allocation was revealed to the surgical team." Comment: surgical personnel were aware of group allocation; unclear whether participants were blinded
Blinding of outcome assessment (detection bias)   All outcomes	Low risk	Quote: "Information on outcome measures was obtained by the research team blinded to the allocation and also not involved in clinical care of the women" Comment: blinded outcome assessment for all outcomes
Incomplete outcome data (attrition bias)   All outcomes	Unclear risk	Quote: "Of the total number randomised, 243 women were inadequately followed up either due to change of address, wrong telephone number or just not receiving the text messages" Comment: 7% of women were lost to follow‐up; this was balanced between the arms (114 versus 129) and between the types of surgery (elective versus non‐elective) undertaken. Although this is close to the wound infection rate it does not appear likely to have impacted on the risk ratio of infection.
Selective reporting (reporting bias)	Low risk	Quote "Primary outcome was the incidence of SSI as a whole but also specifically readmission for intravenous antibiotics and/ or return to theatre for wound infection" Comment: The outcomes were specified in the methods section and then fully reported
Other bias	Low risk	Comment: no specific quote but no evidence of other bias and reporting sufficient to be reasonably confident.