Cochrane in CORR®: Negative Pressure Wound Therapy for Skin Grafts and Surgical Wounds Healing by Primary Intention

Importance of the Topic Postoperative wound complications are among the most devastating experiences following a surgical procedure [1]. Surgical site infections make up approximately 20% of all hospital acquired infections, and studies report infection rates of 2% to 5% among all patients undergoing a surgical procedure [1, 3, 8]. The presence of a postoperative wound infection has been shown to increase the average length of stay by nearly 10 days per patient, with an increased cost of more than USD 20,000 per admission [4] From the patients perspective, those who acquire a deep postoperative infection have been shown to be negatively impacted with respect to their physical, emotional, social, and economic wellbeing, often in a lasting way [1]. Surgical incisions typically heal by primary intention once the skin edges are opposed and secured, but this may be impaired by patient and wound characteristics including age, malnutrition, diabetes, obesity, vascular disease, infection, wound type, and location [2, 12]. Technical reasons may also contribute, including failure of sutures or inadequate stabilization of the wound bed. Negative-pressure wound therapy (NPWT) has emerged during the past 30 years as a solution for managing challenging wounds, including wounds in the setting of postoperative radiation, high-energy trauma, or patients with peripheral vascular diseases [5, 7, 11]. Commercial and noncommercial NPWT dressings create a negative-pressure environment through vacuum suction attached to a foam or gauze dressing sealed with an airtight plastic barrier. This Cochrane review aimed to determine the effects of NPWT on surgical wounds that had been expected to heal by primary intention. Both commercial and noncommercial NPWT dressings were included and compared to standard or advanced dressing across nine trials (796 participants). The authors found the evidence suggesting that NPWT reduces surgical wound complications and time to healing was unclear. From the pooled data on patients, there were no differences in the incidence of surgical site infections (three trials, 232 patients, risk ratio [RR], 1.02, 95% CI, 0.41-2.54); wound dehiscence (one trial, 93 patients, RR, 1.21, 95% CI, 0.65-2.30); reoperation for incisional wounds (one trial, 81 patients, RR, 0.95, 95% CI, 0.41-2.20); seroma/haematoma (one trial, 19 patients, RR, 0.49, 95% CI, 0.23-1.05); or failed skin grafts (one trial, 50 patients, RR, 0.68, 95% CI, 0.32-1.41). Rates of skin graft reoperation may be lower with noncommercial NPWT compared to standard dressings (two trials, 131 patients, RR, 0.42; 95% CI, 0.19-0.92). Furthermore, noncommercial NPWT were shown to be associated with lower pain intensity scores compared to commercial NPWT, with clear cost benefits (noncommercial NPWT: USD 4.22/day versus commercial NPWT: USD 96.51/day, p = 0.01). However, the Cochrane review highlighted a relatively frequent complication associated with NPWT—blistering. Due to the blistering complication, the review recommended limiting the use of NPWT following orthopaedic procedures. Upon Closer Inspection Although nine trials were included in the review, the largest of them had to be analyzed separately for statistical reasons [10]. Stannard and colleagues randomized 249 patients with 263 fractures to receive either a standard dressing (119 patients, 122 fractures) or NPWT (130 patients, 141 fractures) and found that, when analyzed by fracture, there was a decrease in the risk of infection (NPWT group: 14/144, 10%; standard dressing group: 23/122, 19%; RR, 0.52, 95% CI, 0.28-0.96, p = 0.049) and a strong trend towards a decrease in wound dehiscence (NPWT group: 12/139, 9%; standard dressing: 20/122, 16%; RR, 0.48, 95% CI, 0.22-1.03, p = 0.06) [10]. When interpreting results from a randomized controlled trial, it is important to be consistent with units of randomization, observation, and analysis. Stannard and colleagues randomized by patient (n = 249 patients), but later reported the observations and analysis by fracture (n = 263 fractures). As each patient could have multiple fractures, all related wounds for any individual patient would be expected to heal similarly due to underlying patient-related factors, irrespective of treatment allocation [9]. This lack of independence can be adjusted by using advanced statistical tests, although this was not done in the original randomized controlled trial and sufficient information was not available to analyze by individual patients in the meta-analysis. Therefore, the authors of the Cochrane review presented the results from this trial separately, and did not factor it into their final conclusions. While this provides transparency in reporting, it may only serve to further confuse readers by excluding the results from a potentially large and influential trial. Take-home Messages Overall confidence in the pooled results was assessed using the Grades of Recommendation, Assessment, Development and Evaluation framework. This Cochrane review summarizes the available, but very-low-quality evidence suggesting no difference in the rates of wound complications between commercial NPWT and standard postoperative dressings. Further, the writers of this Cochrane review cautioned readers about using NPWT in orthopaedic patients, since one trial was halted prematurely because of an unexpectedly high-risk blistering when NPWT was used after TKA [6]. Researchers found a lower risk of reoperation for skin grafts treated with noncommercial NPWT systems compared to standard dressings, which resulted in a more-favorable cost-benefit profile for noncommercial systems. The reviewers rated down the quality of evidence for serious limitations in study design across all the trials, and very-serious concerns for indirectness due to variation across dressing type, comparators, and wound types as multiple types of NPWT and standard dressings were compared across different types of wounds. There was also serious concern with respect to imprecision and uncertainty around the effect sizes presented. Further high-quality studies are needed to examine the role of NPWT in surgical wounds healing by primary intention, and should focus on both commercial and noncommercial devices, with comparison to a standardized dressing. There is a need for well-conducted trials with concealed allocation, and blinded outcome assessment that examine efficacy and safety in the orthopaedic population, with findings reported in a complete and a consistent manner in-line with other trials assessing NPWT devices.

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