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Topical negative pressure therapy: its place in wound care

Una Adderley
DN RGN BA BSC Msc
Community Tissue Viability Nurse
Scarborough, Whitby & Ryedale PCT

Most wounds heal in a reasonably straightforward fashion, but clinicians will face some woundcare situations that are more challenging. Surgical wounds may dehisce (when the suture line falls apart), and large-cavity wounds with copious exudate may result following debridement of Grade 4 (EPUAP) pressure ulcers.(2) The challenge is to decide on an appropriate plan of care that will adequately manage wound exudate and promote healing while considering the relevant research evidence, the skills of the clinical team, the patient's preferences and the available resources.(3)

What is topical negative pressure therapy?
Wound management has traditionally been based on a combined approach of addressing any underlying pathologies and selecting appropriate dressing materials. However, as the biology of wound healing has become better understood, therapies have been developed that aim to directly intervene with the wound healing process rather than simply promote moist wound healing.(4,5)
Topical negative pressure (TNP) therapy (also known as vacuum-assisted closure [VAC], subatmospheric pressure therapy or dressing, vacuum sealing technique, vacuum-assisted wound closure, vacuum-assisted closure, negative pressure therapy or dressing, foam suction dressing, vacuum compression, vacuum pack, sealed surface wound suction or sealing aspirative therapy) are examples of these more complex interventions.(6)
TNP therapy involves the application of topical negative pressure across the surface of the wound by using open cell dressings (such as gauze or foam) combined with a suction pump. An airtight seal is placed over the wound dressing, and tubing connects the dressing to the pump via a canister to collect exudate.(6) In practical terms, once it has been agreed that a patient is a suitable candidate for TNP therapy, the wound and periwound skin are cleansed and dried in accordance with local guidelines. An appropriate-sized open cell dressing is placed within the wound, and an adhesive drape is applied to cover the wound and periwound skin. A small hole is cut in the drape, sufficient to allow the passage of fluid through the dressing, and the tubing is attached to cover this hole using further drape to secure the tubing. The tubing is then attached to an electronic suction unit via a canister to collect exudate.
There are various biological arguments in support of this technology. It is believed that excess exudate will deter healing in surgical wounds due to the physical presence of the exudate and its chemical constituents. It is also argued that mechanical forces can have an impact on the shape and growth of tissue.6 Therefore, since TNP removes excess interstitial fluid, exerts a mechanical force on the wound bed tissue and maintains a moist wound healing environment, it is possible that this will have a positive effect on wound healing.

When should TNP be used - and when should it not be used?
TNP therapy may be considered as a treatment option for patients with chronic, acute, traumatic, subacute and dehisced wounds, partial-thickness burns, ulcers (such as diabetic or pressure), and flaps and grafts. However, since TNP therapy is a potentially costly therapy, which requires specialist clinical skills, it would only usually be considered for wounds where complicated healing is anticipated. This might be the case for wounds with very heavy exudate that require very frequent dressing change (at least daily), such as orthopaedic trauma wounds, large surgical wounds that have dehisced or been left to heal by secondary intention, or large, deep pressure ulcers. Another potential clinical indication is for wounds with a reduced arterial supply where stimulation of blood flow may enable an adequate circulation to be established, such as arterial leg ulcers or diabetic foot ulcers.

Exuding wounds
When treating wounds that are producing large quantities of exudate, the possibility of an underlying pathology should first be clinically addressed in order to reduce the quantity of exudate. For example, patients with venous hypertension may have a very wet leg ulcer. Providing the patient has an adequate arterial supply to the limb, reversing the venous hypertension by applying multilayer graduated compression will reduce the exudate levels and should promote healing.(7) Patients with wounds that are either infected or heavily colonised with microorganisms may also have high levels of exudate. Treating the infection through systemic antibiotics or topical antimicrobials should result in a reduction of exudate levels. TNP therapy would not be an appropriate first-line therapy for such situations. For wounds with an inadequate arterial supply, surgical intervention to improve arterial supply may be an appropriate first-line intervention.
There are also some situations where TNP therapy is clinically contraindicated. TNP therapy should not be used where there is necrotic tissue or eschar. TNP therapy dressings should not be directly placed over exposed blood vessels and/or organs. TNP therapy is also contraindicated for untreated osteomyelitis, nonenteric or unexplored fistulae and any malignancy in the wound. Precautions should be taken when the patient has active bleeding or where wound haemostasis is difficult to achieve, or when the patient is taking anticoagulant medication. Caution should also be exercised if TNP therapy is to be used in close proximity to blood vessels, organs or exposed tendons, weakened, irradiated or sutured blood vessels or organs, in the presence of bone fragments or sharp edges or with enteric fistulae.

Research evidence is still weak
Although numerous case studies have been published, at present there is no robust evidence to support the use of TNP therapy. A Cochrane systematic review, which examined TNP therapy for treating chronic wounds, found only two small trials.(6) The results of these studies suggested that TNP therapy may be superior to saline gauze dressings in healing chronic human wounds. However, the trials were small and methodologically limited, which meant that the evidence is weak. The Cochrane library has recently published a protocol for a systematic review, which will look at the evidence for TNP therapy for partial- thickness burns, but at present there are no results to report.(8) However, recent non-Cochrane systematic reviews confirm that no robust evidence has yet emerged to support the use of TNP therapy in terms of its clinical or cost-effectiveness.(9)
The lack of supporting evidence leaves clinicians in a difficult situation. Despite the lack of research evidence, TNP therapy is being used more frequently within the hospital setting, with patients subsequently being discharged to the community setting requiring ongoing TNP therapy. TNP therapy may also be initiated within the community setting. Although some TNP components have recently become available on the Drug Tariff, inclusion on the Drug Tariff should not be interpreted as confirmation of clinical effectiveness. Many organisations have ongoing discussions between pharmaceutical advisers regarding the cost of an unproven, costly but prescribable therapeutic intervention and clinicians who regard TNP as a potentially useful tool.
In the absence of robust evidence to guide decision- making, deciding whether TNP therapy is an appropriate treatment for your patient is not easy. If a patient requires more than a daily visit to manage copious exudate, TNP therapy may appear cost-saving in terms of reducing the number of nursing visits and dressings. However, without robust evidence, it is impossible to ascertain whether this will translate into cost-effectiveness.
It is possible that future studies may confirm TNP therapy as a clinically and cost-effective therapy for specific wound care situations. However, as Professor Cullum argued in a recent letter to the BMJ, the current absence of robust evidence coupled with finite healthcare resources means that a costly treatment, such as TNP therapy, should not be viewed as a first-line therapy.(9) Professor Cullum comments that if clinicians advocate such unproven interventions as first-line treatments then it is more likely that patients will be denied more effective treatments as well as making it more difficult to undertake the necessary research.

Conclusion
Until good-quality evidence emerges to inform the debate, clinicians will have to rely on their own clinical judgement. TNP therapy may prove to be another useful tool in the armoury of wound care. However, its relatively high cost (in terms of pump purchase or hire and purchase or prescribing of consumables) means that at present it should be regarded as a second-line therapy that is only used when any other underlying pathology has been adequately addressed and if it is expected to bring significant clinical benefits.

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References

  1. NHS Electronic Drug Tariff. Available from:
    http://www.ppa.org.uk/ppa/edt_intro.htm
  2. EPUAP. Available from: http://www.epuap.org/puclas/index.html
  3. DiCenso A, Cullum N, Ciliska D. Implementing evidence-based nursing:
    some misconceptions. Evid Based Nurs 1998;2:38-40.
  4. Banwell PE. Topical negative pressure therapy in wound care. J Wound Care 1999;8:79-84.
  5. Winter GD. Formation of the scab and the rate of epithelialisation of superficial wounds in the skin of the domestic pig. Nature 1962;193:293.
  6. Evans D, Land L. Topical negative pressure for treating chronic wounds. Cochrane Database of Syst Rev 2001;(1):CD001898.
  7. RCN. Clinical Practice Guidelines: The nursing management of patients with venous leg ulcers. Available from:
    http://www.rcn.org.uk/publications/pdf/
    guidelines/venous_leg_ulcers.pdf
  8. Wasiak J, Cleland H. Topical negative pressure for partial
    thickness burns. (Protocol) Cochrane Database of Syst Rev 2006;4:CD006215.
  9. Cullum N. Not so fast with vacuums and maggots
    as firstline treatment. BMJ 2006;332:1275.

Resources

Cochrane Library
W: http://www.nelh.nhs.uk/cochrane.asp

NHS Electronic Drug Tariff  
W: http://www.ppa.org.uk