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Focus On...Wound Care: Negative Pressure Wound Therapy: An Option for Hard-to-Heal Wounds

January 1, 2006
by Michael S. Miller, DO, FACOS, CWS; Marta Ortegon, PA; Cheryl McDaniel, LPN; and Thomas Serena, MD, FACS, CWS
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    Negative Pressure Wound Therapy (NPWT) is a topical treatment used to promote healing in acute and chronic wounds. It involves the application of negative pressure (suction) to the wound bed. The concept is to turn an open wound into a controlled, closed wound while removing the excess fluid from the wound bed, thus enhancing circulation and disposal of cellular waste from the lymphatic system.1 NPWT consists of a nonadherent, porous wound dressing; a drainage tube placed adjacent to or inserted into the dressing; an occlusive transparent film used to seal the wound and the drainage tube; and a connection to a vacuum pump that supplies the negative pressure. This technique is usually considered only for chronic, acute, and difficult-to-heal wounds. The common applications for NPWT appear in the table.1

The use of negative pressure to promote healing of open wounds has a proven track record for efficacy and ease of use. This article discusses how NPWT works and reviews the documented benefits of this therapy. Two case studies are presented that demonstrate NPWT's efficacy.

How Does NPWT Work?
Two NPWT devices are primarily used in the United States: the V.A.C.« (Vacuum Assisted Closure) TherapyÖ system, offered by Kinetic Concepts, Inc. (KCI), and the Versatile 1« Wound Vacuum System by BlueSky Medical Group. Both use a closed system, meaning that neither the wound nor the components of the treatment are exposed to the air.

The V.A.C. system is applied to an open wound for periods of 48 hours. Suction is directed at the surface of the wound through an interface between the wound surface and either a black polyurethane or white polyvinyl alcohol foam that is cut to the appropriate shape of the wound and is then inserted to contact the entire wound. The less dense, more porous black foam is more commonly used on larger or deeper wounds; the white foam has better nonadherent properties that help protect skin grafts and promote graft survival. The foam allows for distribution of the negative pressure. Suction tubing is placed onto or in the foam, and then the entire wound/foam complex is covered with a clear plastic dressing to seal the wound. It is then connected to a suction pump for 48 hours at either constant or intermittent suction. Suction levels of -125 to -150 mmHg are usually applied. The drainage from the wound goes into a canister attached to the suction pump. Several variations in the size of the pumps and canisters allow for different levels of activity and different treatment locations.

With the Versatile 1 device, a single layer of gauze is placed over the wound, then a flat, silicone Hemovac drain is placed on the gauze over the maximum dimensions of the wound. A second piece of gauze is placed over the drain, creating a gauze "sandwich" around the drain as shown in figure 1. The gauze and drain are entirely covered with a clear, semipermeable dressing that is cut to fit the dimensions of the wound, with a small overlap onto the adjacent healthy skin creating a seal over the wound. The drain is connected to the tubing, which is then connected to the vacuum pump. The gauze is puffy before the vacuum pump is turned on. After the pump is turned on and suction is applied, the cotton gauze collapses and compresses the wound bed. Edema fluid is removed through the drain as shown in figure 2.

Figure 1. Schematic drawing shows the positioning of the Hemovac drain between the two layers of gauze.

Figure 2. Schematic drawing shows a wound to which negative pressure wound therapy is being applied.

Benefits of NPWT
The use of negative pressure to promote healing of open wounds has considerable literature support for efficacy. The effects of NPWT are thought to promote wound healing through multiple actions, including the removal of exudate from the wounds to help establish fluid balance,2 provision of a moist wound environment,3 removal of slough,3 a potential decrease in wound bacterial burden,4 a reduction in edema and third-space fluids,5 an increase in the blood flow to the wound,3-7 an increase in growth factors,8 and the promotion of white cells and fibroblasts within the wound.9 Negative pressure brings tissue together, promoting coaption, which allows the tissues to stick together through natural tissue adherence and increases healing.

There are multiple anecdotal reports and case reports of marked enhancement of wound healing with use of NPWT; however, there are relatively few controlled trials. Gray and Peirce recently conducted a review of the literature currently available on NPWT.5 Results in the studies they reviewed suggest that NPWT may be superior to saline-moistened gauze in promoting healing of chronic wounds, and NPWT may be superior to topical antimicrobial agents and gauze in promoting healing of soft-tissue flaps and skin grafts.5 Philbeck et al found that "healing time can be as high as 61% faster and 38% less costly with combination treatment utilizing a controlled-suction drain system."10