Negative pressure wound therapy for surgical wounds healing by primary closure

Review question

We reviewed the evidence about the effectiveness of negative pressure wound therapy (NPWT) for preventing surgical site infection (SSI).

Background

Surgical site infections are common wound infections that develop at the site of a surgical incision. The incidence of SSI may be as high as 40% for some types of surgery, and may also be higher for people with medical problems such as diabetes or cancer. Surgical site infections increase patient discomfort, length of hospital stay, and treatment costs.

Negative pressure wound therapy involves a sealed wound dressing connected to vacuum pump that sucks up fluid from the wound, which is thought to promote wound healing and prevent infection. In an earlier 2014 version of this review, we found the effectiveness of NPWT to be unclear. This new update includes the results of new trials conducted since that time.

Study characteristics

In February 2018 we searched for randomised controlled trials (studies in which participants are assigned to one of two or more treatment groups using a random method) that compared NPWT with other dressings or with another type of NPWT for the prevention of SSI. We found 25 additional trials, resulting in a total of 30 trials (2957 participants), and two economic studies. The types of surgery included abdominal surgery, caesarean section, joint surgery, and others. The included trials were small, with most recruiting fewer than 100 participants.

Key results

Evidence of low certainty shows that NPWT may reduce the incidence of SSI. We are uncertain if NPWT reduces the incidence of death, dehiscence (reopening of the wound), seroma (excessive fluid under a wound), haematoma (formation of blood clots), readmission to hospital, or repeat surgery. It is uncertain if NPWT results in more dressing-related blisters, or whether the treatment costs more on average than a standard dressing. Results from one trial suggest that NPWT may be more cost-effective than standard care when the impact of an SSI on length of hospital stay and other hospital costs is taken into account.

Quality of the evidence

Most of our results are based on evidence of very low certainty, resulting in a high level of uncertainty in our findings. This was due to a lack of information about the methods used in the trials or a lack of adherence to some of the key standards required for conducting randomised controlled trials. In addition, when a trial involves too few participants, it cannot be accurately assessed if NPWT leads to more benefit or harm. To increase confidence in our results, more high-quality, independently funded trials are needed.

Authors' conclusions: 

Despite the addition of 25 trials, results are consistent with our earlier review, with the evidence judged to be of low or very low certainty for all outcomes. Consequently, uncertainty remains about whether NPWT compared with a standard dressing reduces or increases the incidence of important outcomes such as mortality, dehiscence, seroma, or if it increases costs. Given the cost and widespread use of NPWT for SSI prophylaxis, there is an urgent need for larger, well-designed and well-conducted trials to evaluate the effects of newer NPWT products designed for use on clean, closed surgical incisions. Such trials should initially focus on wounds that may be difficult to heal, such as sternal wounds or incisions on obese patients.

Read the full abstract...
Background: 

Indications for the use of negative pressure wound therapy (NPWT) are broad and include prophylaxis for surgical site infections (SSIs). While existing evidence for the effectiveness of NPWT remains uncertain, new trials necessitated an updated review of the evidence for the effects of NPWT on postoperative wounds healing by primary closure.

Objectives: 

To assess the effects of negative pressure wound therapy for preventing surgical site infection in wounds healing through primary closure.

Search strategy: 

We searched the Cochrane Wounds Specialised Register, CENTRAL, Ovid MEDLINE (including In-Process & Other Non-Indexed Citations), Ovid Embase, and EBSCO CINAHL Plus in February 2018. We also searched clinical trials registries for ongoing and unpublished studies, and checked reference lists of relevant included studies as well as reviews, meta-analyses, and health technology reports to identify additional studies. There were no restrictions on language, publication date, or setting.

Selection criteria: 

We included trials if they allocated participants to treatment randomly and compared NPWT with any other type of wound dressing, or compared one type of NPWT with another type of NPWT.

Data collection and analysis: 

Four review authors independently assessed trials using predetermined inclusion criteria. We carried out data extraction, 'Risk of bias' assessment using the Cochrane 'Risk of bias' tool, and quality assessment according to GRADE methodology.

Main results: 

In this second update we added 25 intervention trials, resulting in a total of 30 intervention trials (2957 participants), and two economic studies nested in trials. Surgeries included abdominal and colorectal (n = 5); caesarean section (n = 5); knee or hip arthroplasties (n = 5); groin surgery (n = 5); fractures (n = 5); laparotomy (n = 1); vascular surgery (n = 1); sternotomy (n = 1); breast reduction mammoplasty (n = 1); and mixed (n = 1). In three key domains four studies were at low risk of bias; six studies were at high risk of bias; and 20 studies were at unclear risk of bias. We judged the evidence to be of low or very low certainty for all outcomes, downgrading the level of the evidence on the basis of risk of bias and imprecision.

Primary outcomes

Three studies reported mortality (416 participants; follow-up 30 to 90 days or unspecified). It is uncertain whether NPWT has an impact on risk of death compared with standard dressings (risk ratio (RR) 0.63, 95% confidence interval (CI) 0.25 to 1.56; very low-certainty evidence, downgraded once for serious risk of bias and twice for very serious imprecision).

Twenty-five studies reported on SSI. The evidence from 23 studies (2533 participants; 2547 wounds; follow-up 30 days to 12 months or unspecified) showed that NPWT may reduce the rate of SSIs (RR 0.67, 95% CI 0.53 to 0.85; low-certainty evidence, downgraded twice for very serious risk of bias).

Fourteen studies reported dehiscence. We combined results from 12 studies (1507 wounds; 1475 participants; follow-up 30 days to an average of 113 days or unspecified) that compared NPWT with standard dressings. It is uncertain whether NPWT reduces the risk of wound dehiscence compared with standard dressings (RR 0.80, 95% CI 0.55 to 1.18; very low-certainty evidence, downgraded twice for very serious risk of bias and once for serious imprecision).

Secondary outcomes

We are uncertain whether NPWT increases or decreases reoperation rates when compared with a standard dressing (RR 1.09, 95% CI 0.73 to 1.63; 6 trials; 1021 participants; very low-certainty evidence, downgraded for very serious risk of bias and serious imprecision) or if there is any clinical benefit associated with NPWT for reducing wound-related readmission to hospital within 30 days (RR 0.86, 95% CI 0.47 to 1.57; 7 studies; 1271 participants; very low-certainty evidence, downgraded for very serious risk of bias and serious imprecision). It is also uncertain whether NPWT reduces incidence of seroma compared with standard dressings (RR 0.67, 95% CI 0.45 to 1.00; 6 studies; 568 participants; very low-certainty evidence, downgraded twice for very serious risk of bias and once for serious imprecision). It is uncertain if NPWT reduces or increases the risk of haematoma when compared with a standard dressing (RR 1.05, 95% CI 0.32 to 3.42; 6 trials; 831 participants; very low-certainty evidence, downgraded twice for very serious risk of bias and twice for very serious imprecision. It is uncertain if there is a higher risk of developing blisters when NPWT is compared with a standard dressing (RR 6.64, 95% CI 3.16 to 13.95; 6 studies; 597 participants; very low-certainty evidence, downgraded twice for very serious risk of bias and twice for very serious imprecision).

Quality of life was not reported separately by group but was used in two economic evaluations to calculate quality-adjusted life years (QALYs). There was no clear difference in incremental QALYs for NPWT relative to standard dressing when results from the two trials were combined (mean difference 0.00, 95% CI −0.00 to 0.00; moderate-certainty evidence).

One trial concluded that NPWT may be more cost-effective than standard care, estimating an incremental cost-effectiveness ratio (ICER) value of GBP 20.65 per QALY gained. A second cost-effectiveness study estimated that when compared with standard dressings NPWT was cost saving and improved QALYs. We rated the overall quality of the reports as very good; we did not grade the evidence beyond this as it was based on modelling assumptions.

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