Negative-pressure wound therapy is a medical technology that helps certain wounds heal by applying controlled suction through a sealed dressing. It is often used for surgical wounds, pressure injuries, traumatic wounds, and some ulcers when a clinician decides that extra fluid removal and protection are needed. The goal is to create a clean, moist, protected healing environment while reducing swelling around the wound.
This treatment matters because better fluid control can support tissue repair and may reduce the number of dressing changes needed.
A typical system includes foam or gauze placed in the wound, an adhesive film that seals the area, tubing, a fluid collection canister, and a portable vacuum pump. The pump creates pressure below atmospheric pressure, often around -75 to -125 mmHg, which gently pulls fluid and infectious material away from the wound. The suction can also help draw wound edges together and encourage blood flow and granulation tissue formation.
Safe use requires correct sealing, pressure settings, canister monitoring, and regular assessment by trained healthcare professionals.
Understanding Medical Technology: Negative-Pressure Wound Therapy
The dressing does more than collect drainage. When the pump lowers pressure within the sealed space, the soft filler transmits that force across the wound surface. At a larger scale, this can help hold wound edges in a more stable position.
At a tiny scale, the filler creates small mechanical pulls on cells. Cells can respond to these forces by attaching, moving, and building new supporting material. This response is called mechanotransduction.
It is one reason clinicians choose a filler carefully. Foam spreads force differently from gauze, and each material may suit particular wound shapes or tissue types.
Fluid movement depends on the difference between pressure near the wound and pressure outside the body. It is affected by more than the pump setting. Thick drainage moves less easily than thin drainage.
A long, narrow tube creates more resistance than a short, wide path. A kinked tube can greatly slow flow. Gravity can matter when the canister is positioned below or above the wound.
The pressure shown by a pump is not always the exact pressure reaching every part of the wound. An air leak lets outside air enter the dressing, weakening the pressure difference.
Many pumps detect this problem and sound an alarm. A dressing that loses its collapsed appearance may be a sign that the seal needs checking.
This therapy supports healing, but it cannot make damaged or dead tissue healthy again. Wounds may first need cleaning or debridement, which means removal of dead tissue by a trained professional. Infection may require other treatment, including medicines or surgery.
During dressing changes, clinicians examine the wound for tissue colour, odour, drainage amount, pain, swelling, and signs of bleeding. Healthy granulation tissue is usually moist and red or pink because it contains many small blood vessels.
New tissue can grow into foam if the dressing stays in place too long, so scheduled changes matter. Negative-pressure therapy may be unsuitable when major blood vessels are exposed, bleeding risk is high, or untreated dead tissue remains.
Students may encounter this technology in hospitals, community nursing, surgical recovery, or care for long-term conditions such as diabetes. Portable pumps can allow some people to move around while treatment continues, though they must follow the clinical instructions for carrying the device and responding to alarms. Patients are not expected to change pressure settings themselves.
When learning this topic, separate the physics from the medical decision. Physics explains why pressure differences move fluid and why a seal matters. Medicine determines whether the treatment is appropriate, which pressure is safe, and when the wound is healing in the right way.
Key Facts
- Negative pressure means the pressure at the wound is lower than surrounding air pressure.
- Common therapy settings are about -75 to -125 mmHg, depending on the wound and clinician order.
- Pressure difference can be written as ΔP = Pinside - Patmosphere.
- Fluid removal rate depends on suction pressure, tubing resistance, dressing seal, and wound drainage.
- A sealed dressing is essential because air leaks reduce suction and make the pump less effective.
- The system usually includes wound filler, adhesive film, tubing, a vacuum pump, and a collection canister.
Vocabulary
- Negative pressure
- Negative pressure is a pressure lower than the surrounding atmospheric pressure, creating suction.
- Wound dressing
- A wound dressing is a sterile covering that protects a wound and can help control moisture and infection risk.
- Canister
- A canister is the container that collects fluid removed from the wound by the suction system.
- Granulation tissue
- Granulation tissue is new connective tissue and tiny blood vessels that form during wound healing.
- Seal
- A seal is an airtight barrier that lets the pump maintain the correct suction at the wound.
Common Mistakes to Avoid
- Thinking stronger suction is always better is wrong because too much negative pressure can damage tissue or cause pain.
- Ignoring a small air leak is wrong because even a small leak can prevent the dressing from maintaining therapeutic pressure.
- Letting the canister overfill is wrong because it can block fluid removal and interfere with pump function.
- Using the device without wound assessment is wrong because some wounds or conditions may not be safe for negative-pressure therapy.
Practice Questions
- 1 A wound therapy pump is set to -125 mmHg relative to atmospheric pressure. If atmospheric pressure is 760 mmHg, what is the absolute pressure at the wound in mmHg?
- 2 A canister can safely hold 300 mL of fluid. If a wound drains 25 mL per hour, how many hours will it take to reach the safe limit?
- 3 Explain why an airtight dressing seal is necessary for negative-pressure wound therapy to work effectively.