Negative pressure wound therapy
What is negative pressure wound therapy?
Negative pressure wound therapy refers to wound dressing systems that continuously or intermittently apply subatmospheric pressure to the surface of a wound to assist healing. Negative-pressure wound therapy is also called vacuum-assisted wound closure (VAC) therapy, It has become a popular treatment modality for the management of many acute and chronic wounds.
How does negative pressure wound therapy work?
The best pressure for wound healing appears to be approximately 125 mm Hg, using an alternating pressure cycle of 5 minutes of suction followed by 2 minutes off suction.
Animal studies have demonstrated that this technique:
- optimises blood flow in the wound bed
- decreases local tissue swelling
- removes excessive fluid that can slow cell growth and proliferation in the wound bed
- decreases numbers of bacteria.
Additionally, intermittent low pressure alters the structure of the cells in the wound bed, triggering a cascade of intracellular signals that increase the rate of cell division and formation of granulation tissue.
Negative-pressure wound devices and placement
There are now several commercially available systems for negative-pressure wound therapy and multiple dressing options engineered for specific wound applications.
Mains-operated systems are available for patients with limited mobility or heavily exuding wounds. Lightweight, battery-powered units have a smaller canister volume suitable for an ambulatory patient with a wound that has minimal to moderate levels of exudate. Units can be programmed to provide varying degrees of pressure either continuously or intermittently.
During the procedure:
- A foam dressing is cut to the approximate size of the wound with scissors and placed gently over the wound.
- A drain tube is placed over the foam.
- The foam dressing, together with the first few inches of the drainage tube and the surrounding area of healthy skin, is covered with adhesive transparent tape.
- The distal end of the drain is connected to the negative-pressure unit, which is programmed to produce the required level of pressure.
- Once the unit is switched on, the air is sucked out of the foam dressing causing it to collapse inwards, drawing in the edges of the wound with it.
- Fluid within the wound is taken up by the foam and transported into a disposable canister within the main negative-pressure unit.
Negative-pressure wound therapy dressings should be changed every 48 hours. If there is infection the dressing should be changed every 24 hours. It may be possible to leave the dressing on for longer periods if the wound is not infected. Depending on the type of wound, negative pressure wound therapy may be needed for 2 – 6 weeks.
When is negative-pressure wound therapy appropriate?
The main reasons for using a mains-powered negative-pressure wound therapy unit are:
- acute surgical and traumatic wounds
- subacute and dehisced wounds
- pressure ulcers
- chronic and open wounds (e.g., venous stasis ulcers and diabetic foot ulcers)
- meshed grafts, to secure the graft in place and/or to accelerate the epithelialisation of the donor site
- adjunct to skin grafts/flap procedures
A battery-powered ambulant negative-pressure unit is recommended for:
- venous stasis ulcers
- lower extremity ulcers
- pressure ulcers
- lower extremity flaps
- dehisced incisions i.e. a condition where the wound has a premature opening or splitting along natural or surgical suture lines due to improper healing
Contraindications for negative-pressure wound therapy
Negative-pressure wound therapy is unsuitable for some wounds.
- fistulas (tunnels) to organs and body cavities (non-enteric and unexplored fistulas)
- necrotic (dead) tissue or eschar that has not been debrided (sloughed-off dead tissue, or a scab)
- osteomyelitis (inflamed bones)
- wounds due to skin cancer
Silver-containing dressings should not be used if the patient is sensitive to these.
Clinical effectiveness of negative-pressure wound therapy
Compared with conventional wound therapy, proposed advantages of negative-pressure wound therapy are:
- better healing of transplanted skin and shorter hospital stay for patients receiving split-thickness skin grafts
- fewer wound infections in patients with wounds following orthopaedic trauma and open fractures
- better wound healing, shorter length of hospital stay, and lower hospital mortality in patients with mediastinitis and unsuccessful wound healing following sternotomy
- better wound healing in patients with diabetes mellitus and gangrene that necessitates amputation.
The effectiveness of negative-pressure wound therapy is less certain in patients with:
- open abdominal wounds
- necrotising fasciitis
- Fournier gangrene (necrotising infection affecting the perineum)
- open wounds after fasciotomy (a surgical procedure where the fascia is cut to relieve tension or pressure)
- tissue defects following musculoskeletal tumour surgery
Benefits of negative-pressure wound therapy to the patient
If this method is successful, benefits may include:
- earlier hospital discharge
- fewer wound dressing changes
- less need for surgery
- savings in nursing costs
- enable transfer from hospital to lower-cost health care setting
- improved quality of life
Disadvantages of negative-pressure wound therapy to the patient
The disadvantages of this form of wound treatment include:
- need to be hooked up to the unit for at least 22 hours a day
- initial pain, due to the application of negative pressure
Negative-pressure wound therapy is not always effective and a non-healing wound may require other, potentially more invasive treatment.
Potential complications of negative-pressure wound therapy
Rarely, complications may occur which may require discontinuation of negative-pressure wound therapy. These may include:
- pressure necrosis (tissue death) from the tubing
- injury to skin around the wound
- growth of granulation tissue into the foam dressing
- increased pain initially, due to reduced pressure as the foam collapses
- contact dermatitis due to the adhesive transparent tape
- fistula (tunnel) formation
- development of skin cancer as a result of increased blood flow in the wound bed (very rare).
Negative-pressure wound therapy may need to be stopped if the patient experiences:
- intolerance or non-adherence to the treatment
- lack of healing
- frank pus in the dressing or canister
- uncontrolled bleeding or blood clot under the dressing.
Cost of negative-pressure wound therapy
The cost of treating wounds with negative-pressure wound therapy is similar to conventional wound treatment but it may have economic advantages or disadvantages in individual cases.