Negative Pressure Wound Therapy (NPWT)
Negative pressure wound therapy or NPWT is a wound treatment based on the use of suction to promote wound healing. It ensures a closed, moist wound environment. Wound fluid or exudate is removed through the dressing into a canister via the tubing when negative pressure is applied. Most systems consist of a filler material, such as gauze or foam, a drape to create a seal, some tubing, and a drain or a port which is connected to a suction pump.
NPWT is suitable for:
- Wounds which are large in size, for example, cavity wounds such as pressure ulcers
- Wounds which have high volumes of exudate
- Wounds which are in awkward areas to dress
- Wounds which need to heal quickly, such as diabetic foot ulcers
- Wounds which are not healing or are slow to heal.
The patient must be comprehensively assessed before treatment is started.
How does NPWT work?
NPWT has the following effects on wounds:
- Removes wound exudate
- Improves periwound blood flow
- Promotes the formation of granulation tissue
- Stimulates cell production.
What are the benefits of NPWT?
The benefits of negative pressure for patients include excellent symptom management, reduced frequency of dressing changes and improvements to the wound. It is also important to recognise that negative pressure can provide a cost-effective alternative to traditional wound therapies due to faster healing times and reduced frequency of dressing changes, which lead to a reduction in overall treatment costs (Searle and Milne, 2010).
What devices are available?
There is a large range of NPWT devices available, which can either be purchased or rented.
Larger devices are generally used for in-patients with larger wounds who are unlikely to be mobilising while receiving therapy. These devices can cope with heavy volumes of fluid and larger wound sizes, such as open abdominal wounds. Canisters for these devices generally hold between 300 and 800mls of fluid.
Medium sized devices are of course smaller, can be used in both hospital and community settings and allow the patient greater mobility, while still managing substantial wounds. Again, these devices may have 300 or 800ml canisters for holding wound exudate.
Smaller, ultra-portable devices are now available which can fit in the patient’s pocket. These devices are battery powered and ultimately designed for smaller wounds with low to moderate volumes of exudate. Some devices have canisters and others manage exudate within a specialised dressing.
Choosing the correct device will depend on the patient’s lifestyle, the size of the wound, volume of exudate, and also the care setting.
When should I use gauze and when should I use foam as a filler for NPWT?
It is important to match the type of filler used with the type of wound you are treating.
Foam dressings need to be cut to the size and shape of the wound to ensure full contact with all the surfaces of the wound bed. This can be difficult when applying the foam to wounds with small areas of undermining. It is suggested in some studies that wounds treated with foam will granulate quicker than those treated with gauze. A foam filler is suitable for acute wounds with large tissue loss and open abdominal wounds.
Gauze conforms easily to the contours in a wound, allowing close contact to all surfaces of the wound bed. The gauze dressing should be used to fill the wound, but should not be compressed or over-packed. It can cause less scarring and contraction so may be more suited to wounds on joints. It is also suitable for abdominal wounds. Very large, irregular wounds with heavy exudate volume, such as deep pressure ulcers can be treated using large rolls of conformable gauze, taking away the need to cut the dressing to fit.
As a general rule, foam dressings are changed every 48 hours and gauze every 72 hours.
When should I discontinue NPWT?
The following may be used as a guideline, but this decision should be made and agreed with the patient and their carer.
Think about discontinuing when there is:
- Decreased wound size: length, width, depth
- Undermining, tunnelling
- Decreased drainage
- Increased granulation tissue
- Increased epithelialisation
- Decreased bacterial burden
- Decreased odour
- Decreased pain
- Patient factors — e.g. if they are unable to tolerate the treatment.
When should I avoid using NPWT?
NPWT is contraindicated for patients with:
- Excessive bleeding
- Untreated osteomyelitis
- Unexplored fistulae
- Malignancy in the wound
- Necrotic tissue with hard eschar present.
Precautions when using NPWT
The following situations may require caution when using NPWT:
- Patients receiving anticoagulation therapy
- Difficult wound haemostasis
- Non-concordant/combative patients
- Untreated malnutrition.
- Ease of use
- Fluid-handling capacity
- Odour control
- Pain control
- Patient comfort
Searle R, Milne J (2010) Tools to compare the cost of NPWT with advanced wound care: an aid to clinical decision-making. Wounds UK 6(1): 106–9