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Wound debridement: methods and results

Una Adderley
DN RGN BA BSC
Community Tissue Viability Nurse
Scarborough,
Whitby and Ryedale PCT

Debridement is the process of removing non-living tissue from pressure ulcers, burns and other wounds. Wounds that contain wet devitalised tissue in the form of slough or necrosis are often unpleasant to both the eye and the nose. Slough and dead necrotic tissue is usually malodorous and causes distress to both patients and their loved ones. Wound malodour may act as a barrier in maintaining close family links because of embarrassment and fear of rejection, and may lead to patients avoiding social events. It can be argued that actively removing slough and dead necrotic tissue will result in a wound that is more aesthetically acceptable to the patient, their loved ones and their clinician.
At the moment there is no evidence to tell us whether debriding a wound helps it heal faster.(1) However, slough is dead tissue, and therefore attractive to colonising microorganisms. Bacterial colonies may produce damaging proteases, which break down the extracellular matrix and prevent granulation and  the formation of epithelialisation tissue. Therefore it is reasonable to assume that removing slough may reduce the risk of colonisation becoming critical and causing infection. Removing slough and necrotic dead tissue will also enable more accurate assessment of the extent of the wound, since devitalised tissue may mask signs of infection and dead spaces may harbour infection.

Debridement methods
In the normal healing process, the body will automatically separate dead tissue from good tissue as shown when eschar (or scab) lifts to reveal the newly healed skin beneath. However, in a chronic wound this process can be delayed or complicated by factors such as excess exudate that can exacerbate rather than resolve problems. In these situations, assisting the body in the debridement process is more likely to improve healing and prevent further deterioration. Debridement may be carried out by a variety of methods:

  • Autolytic debridement.
  • Enzymatic debridement.
  • Sharp debridement.
  • Surgical debridement.
  • Biosurgical debridement.

Systematic reviews on the subject found no evidence from randomised controlled trials to support any particular method of debridement.(2,3)

Autolytic debridement
Left alone, the body will automatically debride dead tissue, known as autolytic debridement. This process can be speeded up by using gels and dressings such as hydrogels and hydrocolloids that increase the debridement rate by donating fluid to the wound. The challenge is to maintain an appropriate level of moisture to promote autolytic debridement without resulting in maceration.
The use of fluid-donating gels and dressings is most useful when the wound contains drier dead tissue such as eschar and dark necrotic tissue. As autolytic debridement proceeds and the dead tissue becomes sloughy, exudate levels will increase. At this point the aim is to maintain a moisture level that will encourage the separation of dead tissue from good tissue while preventing maceration and skin breakdown of the surrounding tissue. The use of a dressing that absorbs exudate while still encouraging debridement (eg, a hydrofibre) may be useful at this point.
Autolytic debridement is a useful method of debridement when a gentle approach is required (eg, fungating wounds). However, the increased moisture levels may carry an increased risk of infection. If this method is considered for patients at high risk of infection (eg, patients with diabetes), this needs to be carefully considered and closely monitored.

Enzymatic debridement
Enzymatic debridement is when an enzymatic drug (usually streptokinase) is applied topically to the dead tissue to remove eschar and necrosis through the digestion of necrotic tissue. However, this method is currently out of favour, partly because it is regarded as a relatively expensive method, but also because of the theoretical risk of overdose if the patient requires streptokinase for a life-threatening condition such as myocardial infarction.

Sharp debridement
Sharp debridement has been defined by NICE as "the removal of dead tissue, with a scalpel or scissors, above the level of viable tissue".(4) It is probably the quickest and most cost-effective method of removing dead tissue but should only be undertaken by a clinician who is competent at this technique. Conservative sharp debridement by a nurse is allowed under the NMC Code of Professional Conduct.(5) Careful attention should be paid to the Code to ensure that the nurse who is undertaking debridement does not breach any of its guidance, in particular the following two points:

  • "Practise competently and possess the knowledge, skills and abilities required for lawful, safe and effective practice without direct supervision."
  • "Acknowledge the limits of your professional competence and only undertake those activities in which you are competent."

It is essential that nurses who carry out sharp debridement not only know how to safely wield a scalpel, but also have detailed knowledge of the anatomy of the particular part of the body that underlies the wound. Sharp debridement requires a skilled practitioner to ensure that only slough is removed, as it can be difficult to differentiate between essential structures and removable slough (eg, top of the foot or hand).
Clinical competence should be achieved through a  competency framework, although at present there is a lack of evidence-based guidelines around this subject.(6)

Surgical debridement
Surgical debridement is the removal of slough using a blade down to bleeding tissue. This obviously requires a very skilled practitioner and anaesthetic but it is quick and effective. Surgical debridement is usually only carried out by a medical practitioner with surgical skills.

Biosurgical debridement
Biosurgical debridement is more commonly known as larvae therapy or maggot therapy. There are historical records of the benefits of using maggots to treat wounds as far back as the 16th century, but these maggots occurred naturally, rather than being introduced as deliberate therapeutic interventions. The first known instance of deliberate therapeutic use of maggots was during the American Civil War. In the first world war, William Baer introduced the use of unsterilised maggots but some patients developed tetanus. During the 1930s sterilisation methods were developed and maggots were commercially marketed. However, the 1940s brought the introduction of antibiotics, and maggot therapy fell out of use. The recent emergence of antibiotic resistance has brought the need to develop alternative methods, and in 1995 the Biosurgical Research Unit at Bridgend started marketing maggots again.
It is unclear exactly how the maggots result in debridement. It is possible that they secrete proteolytic enzymes that liquefy the necrotic tissue, which is then ingested. However, it is also possible that the physical presence of larvae increases the levels of exudate, which washes out bacteria. The larvae secretions may alter the wound's pH levels, which may possibly destroy bacteria and promote healing. It has also been suggested that the movement of larvae may stimulate granulation. At present, much of this is speculation. The University of York is currently carrying out an NHS-funded randomised trial (VenUS 2) comparing maggot therapy with hydrogel for debridement of leg ulcers and hopes to discover whether maggot therapy promotes faster healing.
Maggots, which have been specially bred, are applied directly to the sloughy area of the wound and left for three days. Maggots can be applied "loose" (when the surrounding skin is protected and the maggots are contained through building a nylon net "cage" over the wound) or in bags applied directly to the wound. It is unclear which method is the most clinical, most cost- effective and most acceptable to patients and clinicians. Maggots should not be applied to wounds that communicate with the body cavity or any internal organs, or to wounds that bleed easily or contain exposed large blood vessels. Patients with clotting disorders or receiving anticoagulant therapy should not receive maggot therapy unless they are under constant medical supervision in a healthcare facility. 
Although some patients may refuse maggot therapy, most patients are willing to accept it, and clinician reluctance seems to be more of an issue. Some adverse reactions may be experienced, such as pain or discomfort, which may vary from a mild pricking sensation to pain that is so severe that the maggots need to be removed. Analgesia may help.
Transient pyrexia may also occur and is thought to be due to the absorption of pyrogenic material that is released from the cell walls of Gram-negative bacteria during their passage through the maggots' gut. An antipyretic agent, such as paracetamol, is usually effective in managing this side-effect. 

Conclusion
The choice of debridement method has to be tailored to the needs of the patient and the clinical skills of the nurse. It is possible that debriding sloughy and necrotic wounds may speed up healing. However, even if the evidence eventually shows that this is a mistaken belief, debridement might be viewed as an appropriate palliative measure that often improves the patient's quality of life.

References

  1. RCN Institute. The management of patients with venous leg ulcers. London:RCN; 2006.
  2. Bradley M, Cullum N, Nelson EA, et al. Systematic reviews of wound care management: dressings and topical agents used in the healing of chronic wounds. Health Technol Assess 1999;17(3):2.
  3. Lewis R, Whiting P, Ter Riet G, O'Maer S, Glanville J. A rapid and systematic review of the clinical effectiveness and cost effectiveness of debriding agents in treating surgical wounds healing by secondary intention. Health Technol Assess 2001;5:14.
  4. NICE. Pressure ulcers: the management of pressure ulcers in primary and secondary care. London:NICE; 2005.
  5. NMC. Code of professional conduct. London: NMC; 2004.
  6. Edwards L. Conservative sharp debridement. J Commun Nurs 2005;19(9):16-22.

Resources
Biosurgical Research Unit
W:www.larve.com
Electronic Journal of Wound Management Practice
W:www.worldwidewounds.com