Dear Readers:

Various regimens of subatmospheric pressure, also known as vacuum, negative pressure wound therapy (NPWT), or topical negative pressure (TNP), have been used to manage complex wounds. Limited evidence supports NPWT efficacy on chronic or acute wound healing,^1,2 where it was mainly compared to less than optimal³ saline gauze control dressings. One best evidence review found NPWT to be an acceptable adjunct therapy in managing infected sternal wounds following cardiac surgery.⁴ Reviewers generally agree that large randomized controlled trials (RCTs) are needed to support conclusions of efficacy compared to moist wound dressings (MWD) and to optimize usage regimens. This Evidence Corner summarizes two recent RCTs exploring the effects of different forms of NPWT on partial amputation sites on the feet of patients with diabetes, and split-thickness skin graft take in patients with burns or traumatic wounds, as compared to MWD.

Negative Pressure Wound Therapy Improves Diabetic Foot Amputation Site Healing

       Reference: Armstrong DG, Lavery LA; Diabetic Foot Study Consortium. Negative pressure wound therapy after partial diabetic foot amputation: a multicentre, randomised controlled trial. Lancet. 2005;366(9498):1704–1710.
       Rationale: Diabetic foot amputation sites are often complex and difficult to manage, with “lacklustre” clinical outcomes using many technologies.
       Objective: Conduct an RCT to explore effects of NPWT compared with standard care in managing complex partial amputations on the foot of patients with diabetes managed in wound clinics in private or academic health science centers.
       Methods: A prospective, 18-center, United States-based RCT that met ethical requirements compared healing effects of standard care plus NPWT (n = 77) changed every 48 h to standard care plus MWD (n = 85) using alginate, hydrocolloid, foam, or hydrogel dressings changed every 24 h at clinician discretion. Outcomes measured included percent healed during 16 weeks and time to complete wound closure of amputation wounds on the feet of patients with diabetic neuropathy. Patients included were at least 18-years-old and had adequate perfusion of the study wound, which corresponded to a University of Texas Grade 2 or 3.⁵ All patients received offloading therapy using a pressure relief walker or sandal. Patients with active Charcot arthropathy of the foot, untreated infection, or wounds of etiologies unrelated to diabetes, were excluded. Planimetric wound area measurement was blinded to treatment. Adverse events measured safety aspects of the regimens.
       Results: During 16 weeks, 56% of patients in the NPWT group healed with or without surgical intervention versus 39% in the MWD group (P = 0.04). This included 31 (40%) healing by second intent without surgical intervention in the NPWT group compared to 25 (29%) in the MWD group. NPWT partial amputation sites healed in a median of 56 days compared to 77 days for the MWD group (P = 0.005). The most common type of adverse event was infection—13 NPWT patients (17%) and 5 control patients (6%). There was no significant difference in treatment-related infections.
       Authors’ Conclusions: Negative pressure wound therapy as delivered by V.A.C.^® Therapy^™ (KCI, San Antonio, Tex) was safe and efficacious in treating complex diabetic foot amputation wounds and could lead to a higher proportion healed.

Negative Pressure Wound Therapy Improves Skin Graft Integration

       Reference: Llanos S, Danilla S, Barraza C, et al. Effectiveness of negative pressure closure in the integration of split thickness skin grafts: a randomized, double-masked, controlled trial. Ann Surg. 2006;244(5):700–705.
       Rationale: Complex wounds can be closed effectively using split-thickness skin grafts (STSG). Hematoma or blister formation beneath a STSG reduces the percent of STSG integration into the recipient site and may necessitate re-grafting. NPWT may reduce these complications.
       Objective: Explore the effects of NPWT on STSG integration into recipient sites on patients with full-thickness trauma or burn wounds in regions of skin loss inappropriate for primary closure.
       Methods: A prospective, double-blind RCT of patients with ≤20% total body surface area full-thickness burns or trauma wounds inappropriate for primary closure was conducted in the burn unit of a national referral hospital for work-related injuries in Santiago, Chile, from May 2003–October 2004. After each patient was surgically debrided in the operating room, a fenestrated 0.12-mm thick STSG was harvested using an electric dermatome and sutured or stapled on the same patient’s debrided recipient site. Informed consenting patients were randomized to receive either NPWT (n = 30) or identical control treatment without the vacuum activated (n = 30). Constant –80 mmHg NPWT was delivered at no additional cost through the patient's bedside connection to the hospital central aspiration system through a silicone drainage tube placed over two sheets of high-density open cell polyurethane foam on the wound. The fenestrated end of this tube was covered with a third layer of the same high-density polyurethane foam then sealed with a polyurethane film dressing. Negative pressure levels were checked, and if necessary, the vacuum seal was reinforced with a cotton dressing and an elastic gauze bandage. All wounds remained dressed until the fourth postoperative day when the primary outcome, area of graft loss, was measured. Secondary outcomes were the percent of originally grafted area requiring re-grafting and length of hospital stay (LOS) from intervention to hospital discharge, which usually coincided with complete healing.
       Results: Both groups were similar in demographics and graft characteristics, including total grafted area, which was directly correlated with total area of graft loss. NPWT patients experienced less area and percentage of graft loss (P < 0.001), with and without adjusting for grafted area, LOS, and demographic variables. Fewer NPWT patients (n = 5) required a second grafting procedure compared to control patients (n = 12; P = 0.045). NPWT patients experienced a shorter median burn/trauma unit stay of 8 days compared to 12 days for control patients (P < 0.001). Median hospital LOS for NPWT patients was 13.5 days compared to 17 days for control patients (P = 0.01).
       Authors’ Conclusions: Negative pressure wound therapy is a safe, effective, simple, and inexpensive technique for managing burn or trauma wounds covered with dermal-epidermal grafts.

Clinical Perspective

       These studies support NPWT healing efficacy on diabetic foot amputation sites and on improving STSG take on debrided burn or trauma wound sites. These, plus other recent studies,^6,7 may tip the scale of evidence for NPWT to inform clinical decisions in managing such wounds. Efficacy of different NPWT modalities underscores the need for large RCTs clarifying the ideal NPWT regimen(s) and modalities for each wound etiology or application.
       Both studies described here were on acute wounds so it is uncertain whether the results generalize to chronic wounds. A secondary analysis of the study on diabetic amputations⁸ confirmed similar healing results for “chronic” and “acute” wounds, respectively, defined for the study as existing for more than or ≤30 days. Acute full-thickness wounds may take more than 30 days to heal, so these wounds may have been acute. Dressing changes for the diabetic amputation study were 3 times more frequent for controls than the NPWT group as confirmed by the author, citing an economic analysis of these data (in press) from the American Journal of Surgery. While this difference in dressing frequency was considered essential to maintain wound moisture balance in the study, it may be associated with thermal or other effects of wound exposure. Such artifacts could be controlled in future studies by using an absorbent MWD regimen while wound exudate is high.