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Treating malodorous wounds with silver

Una Adderley
RGN DN BSc BA
Tissue Viability Prescribing Specialist Nurse
Scarborough, Whitby and Ryedale PCT
E:una.adderley@acute.sney.nhs.uk

Malodorous wounds have been defined as "any wound assessed as being offensive (smelly) by the patient, carer or practitioner".(1) Wound malodour is due to the presence of devitalised tissue or stale exudate that has been colonised by bacteria. Malodorous wounds usually contain at least two anaerobic bacteria in addition to aerobic bacteria.(2) Anaerobic pathogens destroy healthy cells by competing for available oxygen supplies and producing toxins that damage healthy tissue. Malodour occurs when the anaerobic bacteria break down proteins in dead tissue, leading to tissue liquefaction and the release of volatile fatty acids with pungent odour.
Malodorous wounds are often misdiagnosed as "infected" despite the absence of other symptoms of infection, such as erythema, heat, oedema, increasing pain, delayed healing or wound breakdown, and dull, friable granulation.(3)
 
Treatment
A wound that displays the above symptoms should be treated with systemic antibiotic therapy. However, a wound that is only malodorous or malodorous with one other possible symptom of infection, such as delayed healing, may be heavily colonised rather than infected. The effective treatment of malodour depends on two principles:

  • Removal of the devitalised tissue and stale exudate.
  • Reduction in the number of colonising bacteria.

Devitalised tissue can be removed, where appropriate, through surgical, sharp or biosurgical (maggots) debridement or through encouraging the natural process of autolysis. An appropriate dressing will keep the wound moist and thus encourage the separation of devitalised tissue from healthy tissue. However, since bacteria are attracted to warm, moist devitalised tissue, this can be a malodorous process, with the attendant risk of infection if the colonising bacteria overwhelm the healing process.
A reduction in the number of colonising bacteria can be achieved through the appropriate use of systemic antibiotics or a topical antimicrobial (such as silver, iodine and so on). In the last few years the wound ­dressings market has been flooded by a variety of new dressings containing antimicrobial agents, and it is now possible to prescribe silver versions of most types of dressings. However, the role of silver in wound care is complex, and the evidence supporting its use is unclear.

Silver
Silver has been used for its anti-infective properties since at least the early 19th century, when surgeons found that silver needles and sutures helped wound healing. Silver as an antiseptic has been used throughout the 20th century in a variety of forms, with silver sulphadiazine succeeding colloidal silver and silver nitrate due to its improved safety and efficacy.(4)
Silver sulphadiazine is a combination of the antiseptic properties of silver with the antibacterial action of sulphonamide drugs. It was introduced in 1968 as a cream or an impregnated gauze dressing that offered a less toxic method than silver nitrate for treating Pseudomonas and gram-positive wound infections, and has since become the antibiotic of choice for burns patients.
The emergence of antibiotic resistance such as methicillin-resistant Staphylococcus aureus (MRSA) has also brought new challenges. Antibiotics and dressings containing silver metal (which includes nanocrystalline silver), silver sulphadiazine, colloidal silver, silver oxide and silver allantoinate appear to offer an effective and safe way of reducing the number of colonising bacteria within wounds.
Wound dressing technology has advanced so that "modern dressings" are designed to meet the characteristics of an ideal dressing. These include the ability to maintain high humidity at the wound site while removing excess exudate, nonadherence, thermal insulation and impermeability to bacteria. Dressings should be nontoxic, nonallergenic and capable of giving protection from trauma. They should be comfortable, conformable, cost-effective, require infrequent dressing changes, have a long shelf-life, and be available in both hospital and community settings.(5)
The need to find alternatives to antibiotics and the evolution of dressing technologies has led to the ­development of sustained-release silver dressings that combine the benefits of modern dressings with the benefits of silver. It is believed that sustained release of silver provides a more effective means of reducing the microbial burden within a wound that causes the symptoms of colonisation, such as delayed healing and malodour, which may lead to clinical infection.
All sustained-release silver dressings share the same main features. They release "active" silver ions in a controlled fashion for a prescribed length of time (usually measured in days). They act upon a broad range of bacteria, including MRSA, and fungi found in the wound bed and thus reduce exudate, malodour and pain. As "modern dressings", they are more likely to be easy to apply, comfortable in use, less painful to change and require less frequent dressing changes, thus leading to improved cost-effectiveness. It is unclear as to whether silver products are any more effective than other antimicrobial dressings such as iodine or honey. However, their incorporation into modern dressing technology would appear to offer benefits in terms of exudate absorption and patient comfort.
Despite dressings being designed to minimise toxic effects, the risk of potential toxicity cannot be eliminated. Silver allergy is rare, but skin rashes, stinging and burning have been reported. Argyria (when silver is deposited in the dermis resulting in a grey/black skin discolouration) has also been observed in some patients treated with silver dressings. Despite knowledge gained from the study of silver nitrate and silver sulphadiazine, there are significant differences between these older products and the way the newer sustained-release silver dressings affect the body. Ionised silver can be absorbed into and distributed through the body, but at present the toxic implications of this are uncertain. Research is needed to identify the minimal silver concentration required to maintain the optimum bacterial load of a wound without toxicity.(6)
A further concern is emerging evidence of bacteria developing resistance to silver antimicrobials, in a similar manner to the emergence of antibiotic resistance. Fortunately, the evidence suggests that silver-resistant strains are not a serious problem with the new dressings.(4) A variety of delivery methods are available, including foams (Contreet foam by Coloplast and Avance by SSL), a hydrofibre (Aquacel Ag by Convatec), a soft polymer (Urgotulle SSD by Parema Urgo), hydrocolloid (Contreet hydrocolloid by Coloplast) and other composite dressings (Acticoat by Smith & Nephew and Actisorb by Johnson & Johnson). The different dressings vary in the amount and form of silver delivered to the wound bed, and there is no clinical evidence to indicate which silver product is the most effective at promoting healing.
A pragmatic approach, however, would be to select a silver dressing based on the symptoms of each wound. For example, a wet, sloughy malodorous wound that is being debrided through autolysis might benefit from the antimicrobial and fluid handling properties of a hydro-fibre, whereas a drier, necrotic, malodorous wound might benefit from a silver hydrocolloid that would encourage autolytic debridement.
Most manufacturers advise that it should be possible to witness an improvement in the wound within 2­-3 weeks if the silver dressing is effective. In most cases, an optimum reduction in the microbial count should occur within a month, and it should be possible to discontinue the silver product without the wound deteriorating. However, in a few cases, the microbial count within a wound will rapidly increase without the silver dressing, and it may be necessary to continue with the silver dressing. It is important to undertake a risk assessment before continuing with the silver dressing.
It is worth noting that maggots don't like silver, or any antimicrobial. Therefore if a silver hydrocolloid is being used to soften devitalised tissue before biosurgical debridement by maggots, a "washout" period without the silver will be required before introducing the maggots.

Conclusion
It is important to remember these practice pointers:

  • Malodour alone is not a sign of infection.
  • Silver wound care products should be prescribed selectively with care and caution.
  • If the silver product is effective then evidence of benefit should be observed within 2-3 weeks.

When used appropriately, sustained-release silver dressings are likely to be useful for promoting healing and reducing the symptoms of heavy microbial colonisation. However, it would seem prudent to prescribe silver wound care products with the same care and caution that should be involved in prescribing antibiotic therapy.

References

  1. Neal K. Treating fungating lesions. Nurs Times 1991;87(23):84-6.
  2. Collier M. Malodour and infected wounds: a patient-centred approach. Leg Ulcer Forum 2001;14:12-4.
  3. Gardner SE, Frantz RA, Troia C, et al. A tool to assess clinical signs and symptoms of localized infection in chronic wounds: development and ­reliability. Ostomy Wound Manage 2001;47(1):40-7.
  4. Lansdown ABG. Silver in wound care and management. Wound Care Soc 2003;1(3).
  5. Bale S. In: Morison M, et al, editors. A colour guide to the nursing ­management of chronic wounds. 2nd ed. London: Mosby; 1997.
  6. Lansdown ABG, Williams A. How safe is silver in wound care? J Wound Care 2004;13(4):131-6.

Resources
World Wide Wounds
W:www.world widewounds.com
LarvE
The official website of the Biosurgical Research Unit, the world's ­leading centre for the production of sterile maggots
W:www.larve.com
Wound Care Society
W:www.woundcaresociety.org
Tissue Viability Society
W:www.tvs.org.uk