How Does NPWT Work?
Two NPWT devices are primarily used in the United States: the V.A.C.[R] (Vacuum Assisted Closure) Therapy[TM] system, offered by Kinetic Concepts, Inc. (KCI), and the Versatile 1[R] 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.
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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.
