Emerging Insights On Negative Pressure Wound Therapy

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Author(s): 
Karen Shum, DPM, and Kazu Suzuki, DPM, CWS

Negative pressure wound therapy (NPWT) has become an indispensable tool for wound care for many physicians. These authors examine the research on NPWT, evaluate the newest devices on the market and provide guidance for getting reimbursement.

Negative pressure wound therapy (NPWT) has become ubiquitous. In 1993, Fleischmann and colleagues reported the early use of NPWT in open fractures to fill wound defects with a foam dressing attached to a tube and canister applying vacuum suction.1 Since that time, NPWT has revolutionized the practice of wound care and all surgical practices dealing with large tissue defects and associated drainage.

   Negative pressure wound therapy was designed to accelerate wound healing via secondary intention by increasing the rate of granulation tissue formation with wound contraction, which expedites the healing process. Indeed, NPWT is valuable in treating acute, sub-acute and chronic wounds of various sizes and depths. This therapy is of utmost importance in diabetic foot ulcers in which fast wound closure is equivalent to limb preservation.

   Negative pressure involves an open cell foam or gauze dressing that one applies to the wound base. The dressing is attached to a tube and canister that collects drainage. Negative pressure is indicated in non-ischemic wounds that have no infected or devitalized tissue. After applying a foam or gauze dressing over the wound base, one would apply negative pressure (75-125 mmHg) uniformly over the foam-covered wound base. The foam collapses and forms channels to transport fluid from the wound to the canister. The removal of interstitial fluid from the underlying tissue enables improved capillary circulation with a reduction in interstitial edema, and allows blood flow to the wound as visible on laser Doppler.2

   Morykwas and coworkers examined the optimal pressure level in a porcine study that showed the effects of low negative pressure of 25 mmHg and high levels of negative pressure of 500 mmHg in comparison to the standard of 125 mmHg on the rate of granulation tissue formation.3 The study authors concluded that the standard subatmospheric pressure of 125 mmHg had the greatest tissue granulation formation rate.

   One would apply suction to the wound in intermittent cycles of five minutes on and two minutes off. A maximum increase in local tissue perfusion occurs with cycling.2 Intermittent therapy causes an increase in cellular proliferation and local growth factors. Chronic non-healing ulcers that arise in diabetic foot wounds have significantly higher levels of matrix metalloproteinases (MMP) in comparison to wounds that are in the process of healing. Enhanced wound healing occurs in both continuous and intermittent cycles by the indirect removal of inhibitory growth factors that occurs with NPWT.4

A Closer Look At The Clinical Evidence Of NPWT

Researchers have observed improved outcomes in diabetic foot ulcers and chronic leg ulcers with the use of NPWT.4 One can also use NPWT concurrently with split thickness skin grafting (STSG) or skin flap techniques as a means for achieving definitive wound closure.

   Deep wounds with exposed muscle, tendon, bone or hardware pose a significant challenge in lower extremity wound healing. These structures require immediate coverage to prevent desiccation, infection and tissue death. Without adequate coverage of these vital structures and hardware, limb loss may ensue.

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