Negative pressure wound therapy (NPWT) is a treatment in which a sealed dressing and a small suction pump apply gentle, steady suction to a wound, to help a hard-to-heal wound close. It is also called vacuum-assisted closure, or a wound vac.
The system has four parts. A piece of foam, or gauze, is cut to fit the wound and placed in it. A clear sticky film covers the foam and seals it to the skin around the wound. A tube runs from the film to a pump. The pump lowers the pressure under the dressing, commonly to about 125 mmHg below normal air pressure, either all the time or in cycles. Fluid from the wound is drawn into a canister on the pump.
How does suction help? It removes fluid that would otherwise collect in the wound and slow its healing. It pulls the edges of the wound together. And it encourages new tissue, called granulation tissue, to grow and fill the wound from below. The dressing is usually changed every two or three days.
The pump's software holds the pressure at the set level, and sounds an alarm if something goes wrong. If the film leaks, the pump cannot hold the pressure. If the tube is blocked, the pressure under the dressing stops changing. If the canister is full, the pump stops. Small battery pumps let patients go home with the dressing on, and some of them are thrown away after one course of treatment.
Healing is tracked over weeks. At each dressing change, a nurse measures the wound, and often photographs it with a tablet app that calculates its area. The measurements are charted in the hospital EHR, so that the doctor can see whether the wound is shrinking.
Say a 61-year-old retired railway employee in Visakhapatnam has a foot ulcer caused by diabetes, 6 cm long and 4 cm wide. His doctor starts NPWT at 125 mmHg below normal pressure, with the dressing changed every three days. After four weeks, the wound measures 4 cm by 2.5 cm. Its size, length times width, has fallen from 24 to 10 square centimetres, and the doctor plans the next step of his treatment.
Foot ulcers like his are common in India, because many people live with diabetes for many years. The long-term care of such patients is described in chronic disease management. NPWT is the reverse of an infusion pump: an infusion pump pushes medicine into the body, while this pump only draws fluid out. When a home pump sends its readings to the hospital, it becomes part of remote patient monitoring.