Emerging Insights On Negative Pressure Wound Therapy
DeFranzo and colleagues have documented the use of NPWT in covering muscle, tendon, bone and hardware in the lower extremity, showing great success.5 Studies also show advantageous effects in the treatment of complex diabetic foot ulcers through faster healing rates, increased proportions of healed wounds and a decrease in the rate of re-amputation.6 In a multicenter, randomized controlled trial involving 342 patients, Blume and coworkers demonstrated that patients treated with NPWT had a greater proportion of healed diabetic foot ulcers and significantly fewer secondary amputations than patients treated with advanced moist wound therapy.7
Negative pressure wound therapy is versatile as it assists granulation tissue formation and consequently prepares the wound bed for STSG placement. A granular wound bed is well vascularized and enables an optimal setting for skin grafting. When applying a STSG, place the foam over a non-adherent dressing covering the skin graft. After applying the negative pressure, the foam conforms to the wound base evenly with the skin graft. This increases graft take by improving skin graft adherence to the underlying wound base. The constant removal of fluid and exudates prevents seroma or hematoma formation.
Additionally, NPWT acts as a bolster dressing and prevents shear forces. Blume and coworkers analyzed the use of NPWT versus a conventional cotton bolster dressing with STSG in reconstructive surgery of the foot and ankle.8 The authors found improved graft survival and less incidence of repeat skin grafting due to complications and failures in comparison to conventional cotton dressings.8,9 With skin grafts, one should leave the NPWT device in place for a range of five to seven days, the time it takes for the skin graft to vascularize.
The principles of using NPWT over an incision are similar in that NPWT keeps the wound edges well coapted during therapy. In the orthopedic trauma literature, Gomoll and coworkers showed the benefits of using NPWT over an incision to reduce postoperative swelling and management of drainage.10 Less frequent dressing changes are required in a closed surgical wound, which may potentially reduce the rate of infection.
The role of decreasing bacterial colonization is debatable with NPWT. Early studies revealed a decrease in bacterial loads in animal models.2 However, subsequent studies evaluating deep tissue specimens show otherwise. There is evidence suggesting that NPWT does not significantly decrease bacterial load but rather changes the bacterial morphology of the wound from non-fermenting gram-negative rods to colonization of Staphylococcus aureus.11 In another study of serial wound cultures, Weed and colleagues found evidence of increased bacterial colonization.12 These outcomes highlight the need for careful wound surveillance, especially in diabetic foot ulcers.
The benefits of NPWT not only include accelerated wound healing but also increased patient comfort by decreasing pain. Since patients can leave the NPWT device in place for several days, it does not require daily dressing changes as one sees with “wet-to-dry” dressings. Some patients may experience dressing change pain. However, one can mitigate this by injecting lidocaine solution into the foam dressing itself, allowing the lidocaine to soak the wound bed for a few minutes.