Negative-pressure wound therapy

Therapeutic technique

Negative pressure wound therapy (NPWT), also known as a vacuum assisted closure (VAC), is a therapeutic technique using a suction pump, tubing, and a dressing to remove excess exudate and promote healing in acute or chronic wounds and second and third degree burns. The therapy involves the controlled application of sub atmospheric pressure to the local wound environment using a sealed wound dressing connected to a vacuum pump. The use of this technique in wound management started in the 1990s and this technique is often recommended for treatment of a range of wounds including dehisced surgical wounds, closed surgical wounds, open abdominal wounds, open fractures, pressure injuries or pressure ulcers, diabetic foot ulcers, venous insufficiency ulcers, some types of skin grafts, burns, sternal wounds. It may also be considered after a clean surgery in a person who is obese. NPWT is performed by applying a vacuum through a special sealed dressing. The continued vacuum draws out fluid from the wound and increases blood flow to the area. In 1995, Kinetic Concepts was the first company to have a NPWT product cleared by the US Food and Drug Administration. Following increased use of the technique by hospitals in the US, the procedure was approved for reimbursement by the Centers for Medicare and Medicaid Services in 2001.

General technique for NPWT is as follows: A dressing or filler material is fitted to the contours of a wound to protect the periwound and the overlying foam or gauze is then sealed with a transparent film. A drainage tube is then connected to the dressing through an opening of the transparent film. Tubing is connected through an opening in the film drape to a canister on the side of a vacuum pump. This creates a moist healing environment and reduces edema. There are four types of dressings used over the wound surface: foam or gauze, a transparent film, and a non adherent (woven or non woven) contact layer if necessary. Foam dressings or woven gauze are used to fill open cavity wounds. Foam can be cut to size to fit wounds. Once the wound is filled, then a transparent film is applied over the top to create a seal around the dressing. The tubing is then attached and connected to the pump. Once the dressing is sealed, the vacuum pump can be set to deliver continuous or intermittent pressures, with levels of pressure depending on the device used, varying between −200 and −40 mmHg depending on the material used and patient tolerance. Pressure can be applied constantly or intermittently.

Negative pressure wound therapy is usually used with chronic wounds or wounds that are expected to present difficulties while healing (such as those associated with diabetes). Non trauma patients are people who might need surgery for conditions such as abdominal infections or cancer. However, it is still not clear how safe and effective NPWT is for treating non trauma patients with open abdomens.

The use of NPWT to enhance wound healing is thought to be by removing excess extracellular fluid and decreasing tissue edema, which leads to increased blood flow and stabilization of the wound environment. A reduction in systemic (e. g. interleukins, monocytes) and local mediators of inflammation has been demonstrated in experimental models, while decreased matrix metalloproteinase activity and bacterial burden have been documented clinically. In vivo, NPWT has been shown to increase fibroblast proliferation and migration, collagen organization, and to increase the expression of vascular endothelial growth factor and fibroblast growth factor 2, thereby enhancing wound healing.