Wound vac (negative pressure wound therapy)

What is a wound vac, and how does it work?

Negative pressure wound therapy (NPWT), often called a wound vac, seals a wound with a dressing and connects it to a small electric suction pump¹. Gauze or foam is cut to the size of the wound, placed on or inside it and sealed with a clear, sticky film. A tube links the dressing to the pump, which gently draws fluid away from the wound into a canister².

It's thought to help healing by drawing the skin edges closer together and increasing blood flow through the tissue, which encourages new tissue to grow³. These ideas are proposed rather than fully proven³. The suction level varies, because there's no single standard setting³.

What is it used for, and how well does it work?

NPWT is used for long-lasting (chronic) wounds, for complex wounds that come on suddenly, and to prepare a wound for a skin graft or flap surgery⁴. Overall, the evidence is low level, and the treatment remains controversial⁴.

Diabetic foot wounds have the most evidence. Compared with ordinary dressings, NPWT may help more foot ulcers heal and may lower the risk of amputation, but the certainty is low and the benefits are modest⁵. It may also shorten healing time⁶.

Other wounds are less clear. For open wounds from injuries, including open fractures, it's uncertain whether NPWT reduces infection³. After bowel cancer surgery on the perineum (the area around the anus), and for breast reconstruction incisions, no clear benefit has been shown⁷⁸. For closed surgical cuts, one health service guide suggests single-use dressings for people at high risk of infection⁹.

Is it right for me?

NPWT is used for long-lasting wounds, wounds from injuries and surgical wounds that have re-opened⁹. It isn't suitable if there is cancer in the wound, untreated bone infection, dead (necrotic) tissue, an unexplored fistula (an abnormal channel) or active bleeding. It also isn't used where the dressing would touch exposed blood vessels, organs or nerves²¹⁰.

If you have a pacemaker, keep the pump at least 10 cm away from it at all times¹⁰.

Most of what's known comes from adults, so if you're older or frail, ask your treating team whether it suits you⁴. In children with burns, NPWT can be harder to apply and treatment can take longer¹¹.

What happens during treatment?

First the wound is cleaned, and the skin around it is dried thoroughly and protected with a barrier film¹⁰. A non-stick layer goes under foam so it doesn't stick to the wound, and deeper wounds need a filler¹⁰.

The dressing is then sealed, the tube is connected and the pump gently applies suction². A trained health professional applies it. The dressing is normally changed three times a week, and the canister weekly unless it fills sooner².

Your team sets a treatment goal at the start and reviews progress at dressing changes. They may stop NPWT when the goal is reached, or if the wound isn't shrinking enough⁹. There's no set number of sessions, so how long you need it depends on your wound.

What are the risks and side effects?

Possible problems include the system failing (a lost seal, a power failure or a blocked tube), wound infection, pain, bleeding, an allergy to the adhesive, sore or broken skin, limited movement, and tissue sticking to the foam¹².

Suction set too high can cause pain and tissue damage, while very low suction tends to be ineffective, so the setting should suit your wound and you¹¹. For wounds from injuries, it's uncertain whether NPWT causes more or fewer side effects than standard care³.

How does it compare with other options?

For a wound that's expected to heal well, ordinary moist dressings are a sensible first step. NPWT is mainly a treatment for long-lasting or complex wounds⁴.

For diabetic foot wounds, it may do better than standard dressings, though how it compares with advanced dressings isn't clear yet⁵. For severe open fractures, it isn't clear yet whether NPWT lowers the risk of infection³.