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Best Practice - Choosing an appropriate antibacterial dressing

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VOL: 102, ISSUE: 44, PAGE NO: 46

Jacqui Fletcher, MSc, PG CertEd, BSc, ILT, RGN principal lecturer, School of Nursing and Midwifery, University of Hertfordshire

The number of different wound dressings has increased considerably in recent years and this has made selecting a dressing for a specific wound more complicated. A variety of concepts have been devised to structure and simplify the process involved in selecting a wound dressing, including the concept of wound bed preparation (WBP).

WBP was first described by Falanga (2000) and Sibbald et al (2000). Falanga (2000) explained that the concept was needed because ‘even the most advanced and sophisticated products require proper wound care and wound bed preparation’. Without adequate preparation of the wound bed it is likely that any product (which may well be expensive) will fail and the clinician will lose confidence in its efficacy.

The concept of WBP supports a systematic approach to wound management (Schultz et al, 2003). Following a holistic assessment of the patient and management of any related issues, for example poor nutrition, WBP encourages the practitioner to evaluate the state of the wound and identify potential barriers to healing. The model identifies three main objectives of care:

  • Debridement;
  • Bacterial balance;
  • Exudate management.

Achieving these key objectives should lead to a stabilised wound and a vascularised wound bed. A variety of models for assessment have been developed to help health professionals focus on the practicalities of assessment. These include the TIME framework (Schultz et al, 2003) and the Applied Wound Management Model (Gray and Cooper, 2005).

Defining wound infection

Deciding whether the presence of bacteria in a wound is a problem is not always straightforward and definitions used to describe bacterial load (the amount of bacteria in a wound) are often unclear and poorly understood. Traditionally, definitions used to describe a wound where bacteria is present include contaminated, colonised or infected. Recently an additional term, ‘critical colonisation’, has been added, to the turning point just before infection develops. If no intervention occurs, local and possibly systemic infection is inevitable (Cooper, 2005). The difficulty for the clinician is that, although these terms are often used in isolation, in practice they occur along a continuum (Kingsley, 2001).

The signs and symptoms used to identify infection in wounds have also been clarified and expanded. In the past the cardinal signs of infection included heat, redness, pain and swelling but these were often confused with inflammation by less experienced practitioners. These signs could be absent in patients who are immunocompromised or have long-term chronic illnesses. In order to more accurately assess for the presence of infection, additional criteria have been proposed by Cutting et al (2005) (Box 1). They also suggest criteria that are specific for different types of wounds (Box 1).

Box 1. additional criteria to assess infection presence

Suggested additional criteria for assessment of presence of infection

  • Delayed healing (compared with normal rate for site condition);
  • Discolouration;
  • Friable granulation tissue that bleeds easily;
  • Unexpected pain/tenderness;
  • Pocketing at the base of the wound;
  • Bridging of epithelium or soft tissue;
  • Abnormal smell;
  • Wound breakdown.

Specific criteria by wound type

  • Acute wounds with primary closure;
  • Acute wounds with secondary healing;
  • Diabetic foot ulcers;
  • Arterial leg ulcers;
  • Venous leg ulcers;
  • Pressure ulcers;
  • Burns - partial thickness;
  • Burns - full thickness.

Treatment of infection

Once critical colonisation or infection has been identified, appropriate treatment should be prescribed. If a wound is infected it is appropriate to use systemic antibiotics. However, where critical colonisation is identified, healing is interrupted or infection is present but there is a poor blood supply, a topical antimicrobial agent may be used either alone or - in the case of overt infection - in conjunction with systemic therapy (Vowden and Cooper, 2006). White (2001) suggests that topical therapy has a number of advantages over systemic therapy (Box 2).

Box 2. Advantages of topical antimicrobial therapy

  • Only the wound and immediate tissues are exposed to the active agent rather than the whole body;
  • Higher levels of antibacterial agent are achieved in the infected wound with
    topical treatment;
  • Reduced exposure to antimicrobials limits toxicity and tissue reaction;
  • The treatment can be multifunctional; for example, it may manage odour and exudate as well as infection.

Selecting an appropriate dressing

There are a wide range of antimicrobial dressings available that contain different antimicrobial agents, including silver, iodine and honey. Criteria have been suggested that may assist in the choice of individual products (Moore and Romanelli, 2006; Vowden and Cooper, 2006). These include:

  • Specificity (is the agent active against the specific bacteria causing the problem in the wound?);
  • Efficacy (does the dressing work? For example, are there sufficient levels of the agent to achieve bacterial kill as opposed to bacterial inhibition and does it do this quickly?);
  • Cytotoxicity (is the dressing likely to damage healthy cells?);
  • Allergenicity (does the dressing contain any materials likely to cause sensitivity or allergy?).

Other considerations include the ability of the dressing to manage exudate and odour, relieve pain and conform to the wound. There is still very little information available to help practitioners choose between antimicrobial products. A systematic review of the use of topical antimicrobials in chronic wounds (O’Meara et al, 2001) could not make recommendations because the trials reviewed were generally of a poor quality. Maillard and Denyer (2006) have suggested a list of features that the ideal antimicrobial dressing should have (Box 3).

Box3. Features of ideal antimicrobial dressing

  • Sustained antimicrobial activity;
  • Provides a moist wound-healing environment;
  • Allows consistent delivery of the antimicrobial in the dressing over the entire surface of the wound;
  • Allows monitoring of the wound with minimum interference;
  • Manages exudate if this is a problem;
  • Comfortable;
  • Provides an effective microbial barrier;
  • Absorbs and retains bacteria;
  • Avoids wound trauma on removal.

Infection may be only one of the problems associated with a wound and other factors, such as moisture balance and debridement, may also need to be addressed. In order to select the most appropriate product, it is important to assess the wound fully and prioritise the objectives. These can then be matched against the characteristics of the dressings available.

Types of antimicrobial dressings

Honey

Most research carried out on honey has focused on the role of manuka honey, which, like most honeys, releases hydrogen peroxide but is also believed to have an additional antimicrobial agent known as the unique manuka factor (UMF) (Gethin and Cowman, 2005). It is widely claimed that honey is able to deodorise and debride wounds and these additional properties may be particularly beneficial in infected wounds. There are no standardised protocols for the frequency with which honey should be applied and the type of secondary dressing that should be used (Gethin and Cowman, 2005).

Silver

This is a broad spectrum antimicrobial, effective against a range of aerobic, anaerobic, gram positive and gram negative bacteria as well as filamentous fungi and viruses; no resistant strains have been discovered (Lansdown, 2002). Despite the absence of resistance in clinical practice, it has been possible to produce resistance in the laboratory setting by using sub-therapeutic levels of silver (Li et al, 1997).

There is controversy about the optimal amount of silver required to achieve a balance between efficacy, toxicity and the potential for resistance. When a silver dressing is selected, the amount of available silver should be considered as well as whether the silver is released from the dressing or the bacteria is drawn into the dressing. Dowsett (2004) notes the importance of choosing a product with a clinically relevant dose of available silver and recommends that treatment stops once the objective for selecting that dressing has been achieved.

Silver products may cause localised discolouration if they come into contact with the skin surrounding a wound; this should wash/wear off within a few days. A rare but more serious complication of using silver products is argyria, which occurs when cells absorb silver salts; this results in a permanent discolouration of the skin. If the silver is absorbed by internal organs it may impair their function.

A large randomised trial of silver products is being undertaken (University of Sheffield, 2006) to compare their efficacy with standard non-adherent dressings underneath compression therapy.

Iodine

Iodine products can cause thyroid disruption. If patients have a history of a thyroid disorder, their thyroid function should be checked before and while using the product. Iodine dressings have a maximum dosage that may be used at any one time and a maximum length of time over which they can be used. The dressing changes colour from deep yellow to white as the iodine is used, clearly showing when the antimicrobial activity is exhausted.

Conclusion

Antimicrobial dressings have an important role to play in wound management but should only be used after careful assessment. Nurses need to establish clear objectives for the dressings that they use and ensure that the product selected can meet these objectives.

The diagnosis of wound infection can be difficult and it is important for nurses to distinguish between inflammation and clinical infection. This requires the practitioner to consider signs other than redness, heat, swelling and pain.

Box 4. antimicrobial dressings:

Summary of key points

Honey

  • Most of research on honey has focused on the role of manuka honey, which is believed to have an antimicrobial agent known as the unique manuka factor (UMF) (Gethin and Cowman, 2005);
  • It is claimed that honey can be used to deodorise and debride wounds;
  • There are no standardised protocols for the frequency with which it should be applied.

Silver

  • A broad spectrum antimicrobial, effective against a range of aerobic, anaerobic, gram positive and gram negative bacteria aswell as filamentous fungi and viruses;
  • No resistant strains have been discovered;
  • Can cause localised discolouration to skin surrounding a wound;
  • Argyria (permanent discolouration) is a rare complication;
  • If absorbed by internal organs it may impair their function.

Iodine

  • Can cause thyroid disruption, so thyroid function should be checked if the patient has a history of a thyroid disorder;
  • Iodine dressings have a maximum dosage and maximum length of time over which they can be used. Manufacturers’ instructions should be followed.

 

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