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Wound care for diabetic foot ulcers

Each week in the UK, 100 people with diabetes will undergo an amputation. Collaborative efforts between nurses, podiatrists and doctors are needed if the number of amputations is to be reduced. This article focuses on the specific role of the nurse with regard to wound care interventions for patients with open diabetic foot ulcers

Una Adderley
DN RGN MSc BSc BA
Community Tissue Viability Prescribing Nurse
North Yorkshire and York PCT

Between 15% and 20% of patients with diabetes will develop a foot ulcer.(1) The risk of lower limb amputation is very high for patients with diabetes and 85% of amputations are preceded by a foot ulcer.(1) The risk of foot ulceration can be reduced through high-quality multifaceted care, which will include good glycaemic control, ongoing podiatry intervention to prevent trauma from pressure and close monitoring for early signs of potential problems. However, inevitably a significant proportion of patients will develop foot ulceration and skilled care will be needed to try to prevent deterioration leading to amputation or even death. 
Wound management of a diabetic foot ulcer is particularly challenging and carries high risks since the diabetic foot is a complex piece of anatomy. The complications associated with diabetes can lead to a variety of issues that need to be addressed. Macrovascular and microvascular changes in the arterial circulation can lead to significant deficiencies in the tiny circulatory systems of the foot resulting in ischaemia. Diabetes can also lead to neuropathic changes. Autonomic neuropathy can reduce the moisture levels in the skin resulting in dry skin that is prone to fissures and cracks. Motor neuropathy may cause foot deformity such as Charcot's foot, which results in the development of pressure points that are vulnerable to skin breakdown due to pressure damage. Sensory neuropathy can mean that a patient with diabetes can damage their foot, but lack sufficient sensation to be aware of that damage. When the underlying susceptibility to infection associated with diabetes is added to ischaemia and neuropathy, the risk of amputation is multiplied.
The keystones to diabetic foot wound management revolve around prevention of infection. In terms of wound management this boils down to minimising the risk of cross-infection, the use of appropriate debridement methods and appropriate dressing selection.

Minimising risk of cross infection
Universal precautions are essential for preventing cross-infection. The usual precautions should be applied such as thorough handwashing and the use of gloves and aprons. Although it is generally accepted that a clean technique is adequate for most chronic wounds (such as leg ulcers) patients with diabetes are particularly vulnerable to infection. Therefore an aseptic technique should be used for dressing changes for patients with diabetic foot ulcers. 

Debridement of dead tissue
Dry dead tissue around a wound can be a source of ongoing trauma and injury. A collar of hard skin around the perimeter of the wound can both impede the blood supply to the wound through pressure and act as a physical barrier preventing the migration of epithelial cells across the surface of the wound. Such callus can also camouflage underlying pockets of infection. Removal is essential to aid visibility, promote adequate assessment and decide on appropriate treatment. 
Wet dead slough within or around a wound is highly attractive to pathogens. There is no robust evidence to suggest that removing slough is essential to achieve healing or even speed up healing. However, removal of slough is generally viewed as a desirable treatment aim in chronic wound care. In the case of diabetic foot ulcers, the suspicion that the risk of infection is increased in the presence of slough provides a good rationale for aggressive debridement.
Debridement can be achieved mechanically or through nonmechanical means. Mechanical debridement includes methods such as surgical debridement (where dead tissue is removed to the level of bleeding tissue) or sharp debridement (where only dead tissue is removed). Surgical debridement is usually preferred for diabetic foot ulcers since it removes all potentially dangerous tissue quickly. However, it should only be performed by a skilled clinician with excellent knowledge of the anatomy of the foot. In practice, this usually means a diabetic podiatrist or a surgeon. Biosurgery using maggot therapy provides an alternative form of mechanical debridement, but will only be effective when the dead tissue is sufficiently moist and soft. Maggot debridement may be more precise than surgical debridement by even a very skilled surgeon, but may carry an increased risk of maceration of the surrounding tissues.
Nonmechanical methods of debridement include dressings that promote autolytic debridement such as hydrogels, hydrocolloids and polysaccharide beads or paste. Hydrogels come in both gel and sheet form but both carry risks. Gels are difficult to keep in place, may "splat" under the pressure of the foot hitting the ground during walking or may macerate surrounding tissue. Sheet hydrogels and hydrocolloid sheets stay in place more effectively, but are occlusive and thus potentially increase the risk of anaerobic bacterial colonisation and subsequent infection. Spun hydrocolloids and polysaccharide beads or paste may allow autolytic debridement while managing exudate; some versions have the added advantage of incorporating a slow release of antimicrobial such as silver or iodine, which may reduce the risk of infection, although at present there is no robust evidence to support this theory.(1)
Decisions regarding the appropriate method of debridement should be carried out in close collaboration with the multidisciplinary team, particularly including the podiatrist.

Dressing selection
Once a clean wound bed has been achieved an appropriate dressing should be selected to promote healing. The evidence suggests that both moisture balance and warmth promote wound healing in acute wounds, and it is likely that these will also be significant factors in chronic wound healing.(2,3) However, achieving moisture balance without maceration is challenging, particularly since inadequately-managed exudate is likely to increase the risk of infection.
Dressings can be usefully divided into those that encourage the donation or maintenance of moisture within a wound (hydrogels and sheet hydrocolloids) and those that absorb moisture (foams, alginates, spun hydrocolloids). The usual aim should be to select a dressing material that is able to maintain a moist wound bed without macerating the surrounding tissue. However, for some patients with severe arterial impairment, it may be decided that moist wound healing presents too high a risk in terms of infection. A surgical opinion should be sought with regard to possibility of revascularisation, but the multidisciplinary team may decide not to pursue moist wound healing if there is little hope of revascularisation. 
Additional dressing interventions that may be useful include the antimicrobials such as silver, honey or iodine. There is no evidence to suggest that honey cannot be used topically for patients with diabetes. However, honey does tend to increase exudate levels and at present there is little evidence of its effectiveness. Similarly, although the dressing market is currently awash with silver-impregnated dressings, to date there is no robust evidence of their effectiveness.1 Iodine is also unproven in this respect.
Topical negative pressure therapy is being used to manage exudate and to possibly reduce bacterial colonisation and promote revascularisation. However, although this technology looks hopeful, at present the evidence to support its use is minimal.4 Similarly, hyperbaric oxygen has not yet been robustly proved to be an effective intervention for healing diabetic foot ulcers.

Diagnosis of infection
Diagnosing infection in a diabetic foot ulcer can be difficult. A wound becomes infected when the susceptibility of the patient is overcome by the virulence of the microbial organism. The signs of infection in chronic wounds are:

  • Increased intensity and/or change in character of pain.
  • Discoloured or friable granulation tissue.
  • Odour.
  • Wound breakdown.
  • Delayed healing.(5)

However, the impaired inflammatory response often found in patients with diabetes can mask these cardinal signs making accurate diagnosis difficult. Antibiotics are generally overprescribed for suspected wound infection, but in the case of diabetic foot ulcers it is usually preferable to err on the side of caution due to the high risks of undiagnosed infection. Similarly, although wound swabbing is overused, early accurate information can make significant differences in outcomes for patients with diabetes. Therefore, although a wound swab should not be used to diagnose infection, it can provide essential data to inform clinical decisions with regard to appropriate antibiotics. In the case of wound infection, suitable systematic antibiotics of sufficient strength for a sufficient length of time are important, but if there is impeded blood flow, topical antimicrobials may also be beneficial. It should be noted that a wound infection in a diabetic foot ulcer can be one of the few wound care "blue light" situations since local infection can proceed to septicaemia very swiftly.  
 
Conclusion
Wound management of diabetic foot ulcers demands close teamwork between specialist diabetic teams and primary care. The risks are high and clinical decisions should err on the side of caution. Close monitoring and close collaboration between all members of the team will help promote healing and minimise the risks of amputation.

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References

  1. Bergin SM, Wraight P. Silver based wound dressings and topical agents for treating diabetic foot ulcers. Cochrane Database Syst Rev 2006;25:CD005082.
  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;193:293-4.
  3. Bryant R. Acute and chronic wounds. Nursing management. 2nd ed. St Louis: Mosby; 2000.
  4. Evans D, Land L. Topical negative pressure for treating chronic wounds. Cochrane Database Syst Rev 2001;1:CD001898.
  5. Gardner SE, Frantz RA, Doebbeling BN. The validity of the clinical signs and symptoms used to identify localized chronic wound infection. Wound Repair Regen 2001;9:178-86.

Resources
Diabetes UK
W: www.diabetes.org.uk
National Diabetes Support team. Diabetic foot guide
W: www.diabetes.nhs.uk/downloads/NDST_Diabetic_Foot_Guide.pdf

CKS. Clinical Topic. Diabetes type 1 and 2 - foot disease
W: http://cks.library.nhs.uk/diabetes_foot_disease/view_whole_guidance