Dressing selection in diabetic foot

Introduction

An initial overview of the literature suggests that ulceration of the lower limb currently affects a substantial proportion of the adult population of the UK in the region of 0.18% and 1.3% depending on the study. (Palfreyman S J et al. 2006). They are most frequently seen in those patients with venous disease, arterial compromise or various forms of neuropathy, all entities more likely to be seen in the adult diabetic. (Fletcher A et al. 2007). Such ulceration is age-related with Lindholm suggesting that 4-5% of the population over the age of 80 yrs actively requiring treatment for these conditions in any one year. (Lindholm C et al. 1999)

Estimates of the cost of treatment in diabetic ulceration of the foot are varied but a definitive study by Oot-Giromini B et al. in the late 1980s put it as high as £200 million then. (Oot-Giromini B et al. 1990)

Before one specifically considers the treatment options of an ulcerated diabetic foot, one should note that the evidence base is both huge and of very variable quality. It is fair to observe however, that because of its comparative prevalence, the ulcerated diabetic foot is treated by a wide variety of healthcare professionals and there seems to be a common consensus that the majority of the treatments currently in use are primarily focussed on maintaining the independence and mobility of the patient with topical applications and a variety of dressings being the most frequently used modalities. The more aggressive forms of treatment, such as vascular surgery, are typically offered to only the most extreme end of the spectrum of presentation. (Griffiths G D et al. 2001)

For the past 50 years, there has been a substantial evidence base to support the view that wound healing is optimal when the wound is kept moist rather than dry. (viz. Winter G D 1962). A number of occlusive or semi-occlusive dressings which promote re-epithelialisation have been developed for chronic wounds to both reduce pain and healing time, to absorb blood and tissue fluids, and (the majority) to be painless on removal. (O'Toole E A et al. 1997)

There is a bewildering choice for the clinician and consideration of the evidence base is vital for optimal dressing selection for each individual ulcerated diabetic foot. Classification of the major occlusive dressings include hydrocolloid dressings (HCDs), alginates, hydrogels, foam dressings (FDs), hydrofiber dressings (HFDs), and paraffin gauze and nonadherent dressings. Newer products designed specifically to enhance angiogenesis or combat infection are hyaluronic acid (HA) as well as dressings that are supplemented with activated charcoal or silver. (Robinson J et al. 2008)

The evidence base has recently been enhanced with a number of meta-analyses which have helped to clarify the therapeutic value of many of the more widely used dressings and it has been noted that different pathophysiologies and aetiologies tend to respond differently to different forms of treatment. (Ryan S et al. 2003)

The most substantial evidence base for treatment is arguably the compression bandage for venous aetiology of the ulcerated diabetic foot and, since its original description by Unna in the late 19th century, it has been modified many times. It requires the continuous application of pressure of between 30 to 40 mm Hg. (Fletcher A et al. 1997 Pg 578). It is capable of achieving healing rates of between 30 - 60% success rates in 24 weeks of treatment and up to 70 - 85% at one year. (Skene A J et al. 1998 Pg 1120 )

Before one considers the optimum dressings for the diabetic foot, one should also note that many studies have considered the effect of treating the factors which reduce healing rates before dressings are applied. This is often omitted from comparative studies, and this can make critical comparative analyses between such studies difficult. (Cormack, D. 2000)

The huge study by Margolis is often cited as a landmark in this area. It is long and complex, but the results can be condensed to show that the factors which were adversely associated with healing included the duration of the wound at time of evaluation, the initial area of the wound, a history of hip or knee replacement surgery, a history of venous ligation or venous stripping, an ankle brachial index of less than 0.80, and more than 50% of the wound covered in fibrin. (Margolis D J et al. 1999)

A brief overview of the BNF(British National Formulary) shows that there are a huge number of dressings available to treat the ulcerated diabetic foot. A short essay cannot hope to cover them all, but it will specifically discuss the merits of Alginate, aquacel foam and hydrocolloid dressings as three illustrative examples.

Alginate dressings

There a number of similar products in this category, all derived from brown seaweed. The main constituent (alginic acid) is biodegraded in the wound to a series of non-soluble calcium salts and soluble sodium salts. Contact with wound exudates causes the dressing to form a gel which can absorb up to 20 times its own weight in fluid. It is therefore primarily indicated in wounds with significant levels of discharge (either infected or non-infected) and contraindicated in dry wounds where further drying could delay healing.

The dressing is typically packed into the wound and a secondary dressing keeps it in place. Infected wounds should have a non-occlusive secondary dressing which will allow easy access and monitoring of the wound base. If the alginate has turned to a gel, it has absorbed the exudates successfully and could be repeated. If it is adherent, then the wound is too dry and a different primary dressing may be indicated.

Aquacel foam

Aquacel foam combines the therapeutic bactericidal action of silver ions with a

foam component which is responsible for a partial fluid lock which can help prevent maceration of the wound edge by the absorbed wound fluid, which is a recognised complication with a number of other dressings. The silver ions become biologically active and bacteriocidal when exposed to fluid in the form of wound exudates. The more exudates that are absorbed by the foam, the more the bacteria come into contact with the ionic silver. The result is a reduction in the bio-burden at the surface of the wound. (Karlsmark T et al. 2003).

Care should be taken with silver containing dressings as, although the silver ions are bactericidal, their presence in too great a concentration can inhibit the healing processes within the wound. Poon et al. showed that sliver can be toxic to both keratinocytes and fibroblasts, which slows down the re-epithelisation of the wound. (Poon, V. K et al. 2004). Current commercial products are aware of this situation and have modified the concentration accordingly, but care must be taken not to change the dressings too frequently.

This type of product is therefore most usefully employed in the ulcerated diabetic foot with moderate to high levels of exudates and particularly those which are overtly infected.

In this context, one should note the remarkably detailed study by Ip et al. which compared the bactericidal activity of the five most commonly used silver-based dressings. (Ip M et al. 2006). It is not appropriate to discuss the results in detail, but each had a different delivery system for silver and this resulted in different profiles of bactericidal activity. There is therefore a case for using the appropriate silver-based dressing for a particular bacterial colonisation of the wound. For example, Staph. aureus colonisation was most effectively treated by Contreet dressings whereas Strep faecalis was eradicated more efficiently by Aquacel foam.

Further decisions would be needed in terms of appropriate dressings, as Jones et al. suggest that dressings that were optimally appropriate for prophylaxis in a non-infected chronic wound could produce at least bacteriostasis with a reduced concentration of silver which would reduce the possibility of impaired wound healing and this could be contrasted with the normal silver based dressings that would be needed for active healing in a wound infected with MRSA for example. (Jones, S. A et al. 2004)

Hydrocolloid dressings

Hydrocolloids are a variety of dressing which are based on gel-forming agents, such as sodium carboxymethylcellulose (NaCMC) and gelatin which is combined with a variety of elastomers and adhesives to form an absorbent, self adhesive, waterproof dressing. When applied most hydrocolloids are impermeable to water vapour, but as the gelling takes place, the dressing becomes progressively more permeable. The loss of water through the dressing in this way enhances the ability of the product to cope with exudate production. (Thomas S et al. 2007)

One should note the comprehensive Palfreyman study which compared the clinical value of the major types of dressing for the ulcerated diabetic foot. (Palfreyman S J et al. 2006) which found that the hydrocolloid dressings, as a group, were of less benefit than foam dressings when used under a compression bandage. There was also an increased incidence of allergic reactions and a higher cost associated with the hydrocolloid group.

Further support for this view came from the huge Viamontes study which found that, although hydrocolloids were effective, they also had the ability to strip skin away from the wound margins and that foam dressings (such as silicone foam) were to be preferred. It also found that the hydrocolloid dressing was more difficult to handle in the clinical situation. (Viamontes L et al. 2003).

Conclusions

A short essay cannot hope to cover all of the ground in this area. One can note that the large Palfreyman meta-analysis added considerably to the evidence base in this area and concluded that, except in well defined clinical areas, such as the presence of a specific infection, there was little evidence to justify the use of one particular dressing over another. In the absence of clear evidence of superior clinical effectiveness, the optimum use of NHS resources should dictate that least expensive appropriate dressing should be used in each case. Patient and nurse preference may be an important factor where there is little difference in cost. An additional factor would be that clinical time is an important cost factor and dressings that require frequent changes may be more expensive than ones that remain in situ. for long periods.

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