Negative-pressure wound therapy
|Negative-pressure wound therapy|
|Other names||Vacuum assisted closure|
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 subatmospheric pressure to the local wound environment, using a sealed wound dressing connected to a vacuum pump. The use of this technique in wound management increased dramatically over the 1990s and 2000s and a large number of studies have been published examining NPWT. NPWT has many indications for use including:
- Dehisced surgical wounds
- Closed surgical wounds
- Pressure injuries or pressure ulcers
- Diabetic foot ulcers (DFUs)
- Venous insufficiency ulcers
- Skin flaps and grafts
- Management of the open abdomen (laparotomy)
NPWT promotes wound healing 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. The vacuum may be applied continuously or intermittently, depending on the type of wound being treated and the clinical objectives. Typically, the dressing is changed two to three times per week. The dressings used for the technique include foam dressings and gauze, sealed with an occlusive dressing intended to contain the vacuum at the wound site. Where NPWT devices allow delivery of fluids, such as saline or antibiotics to irrigate the wound, intermittent removal of used fluid supports the cleaning and drainage of the wound bed.
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: "protect the periwound by applying a skin barrier." A dressing or filler material is fitted to the contours of a wound and the overlying foam or gauze is then sealed with a transparent film. A drainage tube is 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. or vacuum source, turning an open wound into a controlled, closed wound while removing excess fluid from the wound bed to enhance circulation and remove wound fluids. This creates a moist healing environment and reduces edema. "There must be an air tight seal in order for this therapy to be successful." The technique is usually used with chronic wounds or wounds that are expected to present difficulties while healing (such as those associated with diabetes).
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.
The dressing type used depends on the type of wound, clinical objectives and patient. For pain sensitive patients with shallow or irregular wounds, wounds with undermining or explored tracts or tunnels, gauze may be used, while foam may be cut easily to fit a patient's wound that has a regular contour and perform better when aggressive granulation formation and wound contraction is the desired goal.
- Malignancy in the wound
- Untreated osteomyelitis
- Non enteric and unexplored fistulas
- Necrotic tissue with eschar present
- Exposed blood vessels, anastomotic sites, organs and nerves in the periwound area (must avoid direct foam contact with these structures)
A 2020 Cochrane Review assessed the effects of NPWT for preventing surgical site infection (SSI). The review authors included evidence from 44 studies and concluded that "NPWT for surgical wounds healing by primary closure probably reduces the rate of SSI compared with standard wound dressings". Due to a large number of ongoing studies the authors note that the review findings may need updating as new evidence emerges and that "Decisions about use of NPWT should take into account surgical indication and setting and consider evidence for all outcomes."
A 2007 Cochrane Review stated that the evidence comparing NPWT to alternative care was flawed and required more study, but the evidence did support improved healing and called for more, better quality research to be conducted. A 2008 study evaluated the efficacy of NPWT compared with advanced moist wound therapy (AMWT) to treat diabetic foot ulcers. A greater proportion of foot ulcers closed with NPWT (43.2%) than with AMWT (28.9%). A 2010 systematic review found "consistent evidence of the benefit of NPWT" in the treatment of diabetic ulcers of the feet. Results for bedsores were conflicting and research on mixed wounds was of poor quality, but promising. The review did not find evidence of increased significant complications. The review concluded "There is now sufficient evidence to show that NPWT is safe, and will accelerate healing, to justify its use in the treatment of diabetes-associated chronic leg wounds. There is also evidence, though of poor quality, to suggest that healing of other wounds may also be accelerated." The use of NPWT to enhance wound healing 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.
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