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Wound Therapy with Negative Pressure

Negative Pressure Wound Therapy (NPWT): A Better Solution for Complex Wounds
Jennifer Weh, DVM, DACVS-SA

Wounds are a common cause of morbidity in our patients, and management of complex wounds can be prolonged and debilitating, leading to long hospital stays, painful and labor-intensive bandaging, and significant financial hardship. The most successful wound care plan takes into consideration all of the components of a wound (depth, degree of contamination, size, location, chronicity) as well as the clinical presentation of the patient (systemic health, personality, age). We have come a long way from the time of the wet-to-dry bandage, and today there are a number of moist wound care products to choose from that follow the typical course of healing through inflammation, proliferation and finally maturation.

Negative pressure wound therapy (NPWT) is a wound healing modality that intervenes at the proliferation stage of healing and has some pretty amazing results. Functionally, NPWT is the application of subatmospheric pressure to a wound bed, open or closed, through foam dressing. This results in decreased interstitial edema, reduced bacterial load, the creation of a closed environment, improved circulation and enhanced granulation bed formation. While there’s never only one way to treat a wound, I have found that in some cases NPWT is the most efficient path to resolution. Faster granulation bed formation means fewer trips to the hospital, fewer bandage changes and often sets the stage for earlier delayed primary closure.

Nuts and bolts of bandage application

NPWT bandages have to be applied at the right time to the right wounds. They have no part in the debridement phase of a dirty, devitalized or infected wound. After adequate debridement (that may take several days), the bandage is applied. This consists of open cell foam covered by adaptic dressing placed within the wound bed. Skin edges can be advanced to the foam edges as determined by the wound configuration. Adhesive drape material covers the entire dressing and tubing that connects the foam to a vacuum pump and collection reservoir. Negative 125 mmHg is an adequate setting for most applications, and the bandage can stay in place for up to 72 hours. Most commonly, NPWT therapy is used for 3 to 6 days, but the bandage is often only changed once under moderate sedation. This results in a hospitalized patient who needs less sedation or anesthesia, gets more consistent nutrition, and is more comfortable and amenable to treatment.

CASE 1, Photos

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Case 1, Photo 1: Placement of foam dressing within a septic incisional dehiscence wound

Case 1, Photo 2: After placement of tubing and adhesive dressing

Case 1, Photo 2: After placement of tubing and adhesive dressing

Case 1, Photo 3: After 6 days of NPWT

Case 1, Photo 3: After 6 days of NPWT

Case 1, Photo 4: Closure

Case 1, Photo 4: Closure

CASE 2, Photos

Case 2, Photo 1: Multiple wounds, such as these bite wounds, can be treated in one bandage.

Case 2, Photo 1: Multiple wounds, such as these bite wounds, can be treated in one bandage.

Case 2, Photo 2: Foam bridges connect wound dressings.

Case 2, Photo 3: After placement of the adhesive

Case 2, Photo 3: After placement of the adhesive

Case 2, Photo 4: Patients are comfortable with the NPWT bandage in place.

Case 2, Photo 4: Patients are comfortable with the NPWT bandage in place.

How does it work?

The application of uniform negative pressure to a wound bed removes from the area interstitial fluid that contains high levels of inflammatory cytokines and proteases in chronic wounds. It also helps to decrease the local pressure which can decrease perfusion pressure and restore blood flow to previously collapsed capillaries and lymphatics.1 Negative pressure also has a direct effect on blood vessels by increasing vascular diameter and blood velocity and by initiating earlier angiogenesis – within the first hours of the application of negative pressure.2,3 Negative pressure also deforms tissue by deforming the skin edges and limiting the loss of domain that happens when wound edges naturally retract. On a microscopic level, the mechanical force of microdeformation has a fundamental role in regulating tissue growth by placing traction on the extracellular matrix and thereby turning on growth factors that regulate cellular proliferation.4 This is similar to the Ilizarov technique of distraction osteogenesis, which is based on the principal that tissue, in this case bone, responds to mechanical tension. Finally, NPWT stabilizes the wound environment by creating a semipermeable membrane that keeps ongoing contamination out, provides an appropriate electrolyte balance and maintains body temperature. Under these conditions and through these mechanisms, granulation tissue is enabled to form more quickly.

 Case selection

NPWT was developed for humans to treat diabetic ulcers and open fractures. Since its inception over 500 peer-reviewed articles have been published in the human literature reporting its efficacy. Veterinarians have adapted the use of NPWT to our patients over the past 15 or so years, but evidence of efficacy is sporadic. Excellent evidence supports the use of NPWT in early treatment of distal extremity shearing wounds5 and to stabilize full thickness skin grafts.6 It was confirmed to speed the formation of smooth, nonexuberant granulation tissue in acute wounds7 and as an acceptable modality in treating traumatic wounds.8 Veterinarians at the University of Florida have reported its successful use in other applications including skin avulsions, degloving injuries, abdominal and thoracic wounds, surgical dehiscence, chronic nonhealing wounds, to prevent postoperative edema and myofascial compartment syndrome.9 NPWT is contraindicated in a few cases in which cancer cells or overexposed vessels are present in the wound bed, in the face of active bleeding, or in devitalized tissue beds. Complications are few and are usually technical issues related to the application or use of the system. Mild skin irritation of surrounding skin can develop from the tissue adhesive and drape. In my experience, as with any wound care tool, NPWT works best in carefully selected wounds. It has proven significantly effective in our patients in many traumatic wounds resulting in more comfortable and earlier wound closure. Let us help you to determine if NPWT may be helpful in your complicated wound cases.