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Wound care: dressings and topical treatments

Una Adderley
RGN DN BSc BA
Research Nurse
Centre for Evidence Based Nursing
Department of Health Studies
University of York
District Nurse Scarborough and NE Yorks NHS Trust
E:una.adderley@virgin.net

In 1995 there were over 400 brands of wound dressing and treatments on the market, and new products are emerging all the time. Wound care is likely to absorb the majority of the nurse prescribing budget. The technological advances of our times are being applied to topical treatments, such as laser therapy and therapeutic ultrasound, in the hope of discovering new clinical applications that will improve patient care.
Despite the need for responsible and accountable decision making, it can be tempting to try anything and everything, or alternatively to stick with conservative traditional products and methods. However, the best wound care should be an informed balance between evidence, ­experience and innovation.
Wounds are dressed "to provide the optimum environment for the natural healing processes to take place".(1) The usual aim is to identify the wound dressing or treatment that will most effectively manage the symptoms of the wound to promote healing. To achieve this the clinician will need to have correctly identified the aetiology of the wound, considered the research evidence for a particular type of dressing or treatment, taken the patient's preferences into account, and have the resources to obtain and apply the dressing or treatment with the necessary frequency.
There is still relatively little research evidence with regard to the characteristics of the ideal wound dressing, but it is generally accepted that moisture and thermal insulation are significant. The principle of moist wound healing was first highlighted in the 1960s,(2) when Winter found that maintaining a moist wound bed speeded up epithelialisation in acute wounds in young pigs. This principle has been widely adopted. However, maintaining a moist wound bed may be inappropriate for some types of wounds that are particularly prone to infection, such as necrotic digits or diabetic foot ulcers. When considering whether to adopt the principles of moist wound healing, the clinician will need to balance the chances of swifter epithelialisation against other risks.
With regard to thermal insulation, there is in-vitro evidence that drops of temperature below 37˚C delay mitotic activity by up to four hours, while a drop of only 2˚C in temperature reduces leukocyte activity.(3) Therefore it is likely that cleaning a patient's wound with a cool solution or applying a dressing that gives no ­thermal insulation will reduce the rate of cell repair and increase the risk of infection.
Expert opinion suggests that the ideal wound dressing should be able to maintain high humidity at the wound site while removing excess exudate, be non-adherent, thermally insulate and be impermeable to bacteria. It should be nontoxic, nonallergenic and capable of providing protection from trauma. It needs to be comfortable, conformable, cost-effective, require infrequent dressing changes, have a long shelf-life and be available in both hospital and community settings.(1)
Decision making regarding dressings and topical treatments can be assisted by the adoption of wound management policies, protocols, NICE (National Institute of Clinical Excellence) guidelines, patient group directives and formularies. However, all these can act only as a guide to decision making; the individual prescriber still holds the final responsibility for the selection of a particular dressing or treatment.
The British National Formulary divides dressings into seven categories:

  • Alginates.
  • Foams.
  • Hydrogels.
  • Hydrocolloids.
  • Vapour-permeable films and membranes.
  • Low-adherence dressings and wound contact materials.
  • Odour-absorbent dressings.

Alginate dressings
Alginate dressings can be used for moderate to heavily exuding wounds since they absorb liquid to form a moist gel. Sodium ions are exchanged for calcium ions, which can be useful for promoting haemostasis. Alginate dressings are highly absorbent, conform to the wound shape, are biodegradable and available on prescription. However, they will require a secondary dressing and need changing every two to three days. Alginates may not be appropriate where the wound contains friable blood vessels, and the manufacturers do not recommend these dressings for dry wounds.

Foam dressings
Foam dressings are highly absorbent, have low adherence and provide good thermal insulation. They do not shed fibres or particles and since they are designed to be fully permeable the dressing should not be covered by occlusive tape or film. Dressings should be changed when strikethrough occurs, and foam dressings are not recommended for dry shallow wounds as drying exudate can lead to adhesion to the wound bed. Foam cavity dressings have recently become available on prescription along with the other foam dressings.

Hydrogels
Hydrogels are available as gels, sheets and pastes. They generally donate fluid to dry wounds to encourage autolytic debridement and prevent adherence to secondary dressings, although some hydrogels are designed to debride and absorb exudate. Hydrogels are relatively permeable to gases and provide a barrier to microorganisms. They are useful for desloughing light to medium exudating wounds but can lead to maceration around the wound. Some hydrogels provide a cooling sensation that may ease wound pain, but this must be balanced against the reduction in healing associated with cooling a wound.

Hydrocolloids
Hydrocolloids are usually manufactured as an absorbent layer on a vapour-permeable film or foam, although a nonocclusive fibrous hydrocolloid has recently become available. The particles absorb water to form a gel that rehydrates and insulates the wound. Hydrocolloids have low adherence and are flexible and conformable but have limited absorption. As an occlusive dressing they create a hypoxic environment that is thought to stimulate the creation of new blood vessels but may also increase the risk of anaerobic infection. Hydrocolloids can be very effective at softening eschar and promoting granulation but are not recommended for infected or heavily exuding wounds. The hydrocolloid gel that arises from exudate can have a distinctive malodour that patients may find unacceptable, and there is a risk of maceration around the wound. Most of the hydrocolloids are available on prescription.

Vapour-permeable films and membranes
Vapour-permeable films and membranes are permeable to vapour and oxygen but impermeable to microorganisms. They are transparent and can provide prophylaxis against friction but little thermal insulation or absorbency.

Low-adherence dressings
Low-adherence dressings include absorbent perforated film dressings that provide an absorbent dressing with a film surface to discourage adherence. Knitted viscose dressings have an open structure that allows free passage of exudate, but they will require a secondary dressing. Both types of dressing can be a cheap solution for dry or lightly exuding wounds but carry the risk of maceration and adhesion. Tulle dressings are impregnated with yellow soft paraffin or a medication. Medication-impregnated tulle is not usually recommended for wound care due to doubts about efficacy, the high incidence of hypersensitivity and risk of systemic toxicity due to absorption. Paraffin-impregnated tulle can lead to maceration as the exudate cannot escape and the wide weave creates a risk of granulation occurring through the weave.

Odour-absorbent dressings
Odour-absorbent dressings usually contain activated charcoal that absorbs toxins, wound degradation products and the volatile fatty acids that cause odour. The fibres become microporous, increasing absorption, and some have the ability to bind bacteria. They can be useful for discharging purulent and contaminated wounds that are complicated by bacterial infection and odour. However, it is unrealistic to expect these dressings to independently manage malodour: treatment of the cause of malodour should be considered.

Research
Although trials exist comparing individual dressings, the evidence base comparing different types of dressings is currently fairly limited. A systematic review that considered dressings and topical agents used in the healing of chronic wounds found no reliable evidence in favour of any particular type of dressing for surgical wound healing by secondary intention.(4) There was some evidence that hydrocolloids may promote healing for pressure sores. There was also some evidence that for venous leg ulcers being treated with multilayer compression bandaging, low-adherence dressings were as effective as hydrocolloids.
At present there is also little evidence with regard to adjuvant therapies such as skin grafts, laser treatment, ultrasound, electrotherapy or magnet therapy. A recent systematic review of wound care management using laser therapy, therapeutic ultrasound, electrotherapy and electromagnetic therapy found insufficient evidence on whether any are beneficial in treating wounds.(5) Another recent systematic review was also unable to find any reliable evidence supporting the use of topical negative ­pressure (TNP) for treating chronic wounds.(6)
This current shortage of reliable research evidence may seem discouraging. However, we can only hope that this situation will encourage clinicians who are seeking good quality evidence to be willing to become involved in quality trials that will increase the body of knowledge.
When making wound management decisions, it is important to balance all considerations. Ideally, the aim should be to promote swift wound healing in the most cost-effective way through using research evidence with the concordance of the patient. Unfortunately, life is often not that simple. Some wounds will never heal, research and cost-effectiveness evidence may not yet be available, and the patient may refuse all our best-intentioned advice. However, these challenges should not deter the clinician from aiming to offer the best possible evidence-based wound care available.

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References

  1. Bale S. Wound dressings. In: Morison M, Moffatt C, Bridel-Nixon J, Bale S, editors. A colour guide to the nursing management of chronic wounds. 2nd ed. London: Mosby; 1997.
  2. Winter GD. Formation of the scab and the rate of epithelialisation of superficial wounds in the skin of the young domestic pig. Nature 1962;193(4812):293-4.
  3. Bryant RA. Acute and chronic wounds. 2nd ed. St Louis: Mosby; 2000.
  4. Bradley M, Cullum N, Nelson EA, Petticrew M, Sheldon T, Torgerson D. Systematic reviews of wound care management: (2) dressings and topical agents used in the healing of chronic wounds. Health Technol Assess 1999;3(17 Pt 2):iv.
  5. Cullum N, Nelson EA, Flemming K, Sheldon T. Systematic reviews of wound care management: (5) beds; (6) compression; (7) laser therapy, therapeutic ultrasound, electrotherapy and electromagnetic therapy. Health Technol Assess 2001;5(9):144.
  6. Evans D, Land L. Topical negative pressure for treating chronic wounds (Cochrane Review). In: The Cochrane Library, Issue 2, 2001. Oxford: Update Software.

Resources
Department of Health. Drug tariff. London: HMSO; 2002.
British Medical Association and Royal Pharmaceutical Society of Great Britain.
British National Formulary. March 2002.
Cochrane Library of Systematic Reviews
W:www.cochrane.org
National Electronic Library for Health
 (gateway to numerous evidence-based materials)
W:www.nelh.nhs.uk
EBN Online
Website of Evidence Based Nursing (journal containing
peer-evaluated research)
W:www.evidencebasednursing.com
World Wide Wounds
(an online resource for dressing materials and practical wound ­management information)
W:www.worldwidewounds.com
European Wound Management Association
W:www.ewma.org