Debridement: wound bed preparation

The word ‘debridement’ dates back to the sixteenth century where it literally translated from French as to ‘remove a bridle’ or ‘a constraint’. The term was later used in the eighteenth century in a surgical context in relation to gunshot wounds as ‘wound incision’ in French and later to ‘wound excision’ in English (Saadia & Schein, 2000). The aim being to rid the wound of any contaminated and devitalised debris to reduce the risk of infection. The modern day interpretation of the term still links to the need to cleanse and prepare the wound for healing, but frequently in a less invasive manner.

Wound debridement

There are two well established aims of debridement; firstly, to remove tissue contaminated by bacteria and foreign bodies and secondly, to remove permanently devitalised (dead or ischaemic) tissue (Westaby, 1985). Debridement is viewed as an essential component of wound bed preparation the aim of which is to create an optimal wound healing environment by producing a stable, well-vascularised, minimally exuding wound (Vowden & Vowden. 2002). Failure to remove devitalised tissue can lead to infection, generalised sepsis and failure to heal or reduce in size (O’Brien, 2002).

Wound bed preparation is what we have always done and is therefore not a new concept; the difference is that increasing knowledge of the healing process at cellular level combined with the realisation and acknowledgement that systemic disorders will positively or negatively influence healing rates and successful management.

Cleansing the wound

Healthy skin is home to natural commensals such as Staphylococcus epidermidis, Mycobacteria, Propionibacterium (anaerobic) and Corynebacterium most of which are gram⁺ aerobes. It follows that all open wounds will be colonised by commensal flora and, depending on a range of factors both internal and external to the patient, may or may not cause infection. Wound infection is caused by pathogenic microorganisms evading the victim’s immunological defences, entering and establishing themselves within the host’s tissues, and multiplying, causing a host reaction (Collins et al., 2002). Accurate management of wound infection is dependent upon identifying and treating the infecting organism.

The presence of devitalised tissue in a wound will increase the risk of infection as micro-organisms evade the host immunological defences, establishing themselves and multiplying, causing a host reaction (Collins et al., 2002). Early removal of necrotic tissue should reduce the risk of contamination and infection thereby facilitating healing.

Competencies for debridement

While the most suitable method of debridement should be selected, the competence of the practitioner must be carefully considered. The practitioner must have a working knowledge of the range of debridement methods but recognise his/her professional limitations and accountability in terms of knowledge, training and competence. In view of this, for example, the vast majority of nurses will not be trained and in a position to sharp debride a wound, and should know when to make a specialist referral to the tissue viability service for advice. Safety is the key issue and the risks and benefits carefully weighed before a decision is made, in conjunction with the patient, and with their informed consent.

Devitalised tissue

In simple terms, tissue in the wound bed dies due to the lack of blood supply; however, underlying and/or untreated pathological clinical conditions such as diabetes mellitus or vascular disease or external mechanical factors will have contributed to the initial wound and will influence its longevity. This is recognised as necrotic burden which will persist for as long as the underlying systemic condition remains uncontrolled (Ayello & Cuddigan, 2004). Lack of blood supply causes death at a cellular level, the dead cells accumulate in either a dry or wet mass which is recognised as necrotic tissue or slough. The thick, leathery, dried-out, brown or black appearance suggests necrotic tissue or eschar. Slough, which presents as white, cream,

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Figure 1: Sacral pressure ulcer - post surgical debridement.

yellow tenuous (tethered), fibrinous tissue, comprises a complex mixture of fibrin, deoxyribonucleo-protein, serous exudate, leucocytes and bacteria. Slough and devitalised tissue will act as a bacteriological culture medium and inhibit the action of leucocytes in a wound and thus predispose a wound to infection (Mulder et al., 2002).

Contributing factors

Examples of intrinsic and extrinsic factors that influence the rate of healing include pressure, infection, dessication, trauma, nutritional status, pre-existing and current medical conditions, and the presence of necrotic tissue (Hess, 2002). Enoch and Harding (2003) highlight the complexity of the normal healing process and suggest a combination of three approaches:

• Treatment of underlying medical problems;
• Assessment and treatment of local wound bed;
• Effective management of any patient-centred concerns.

The aim being to achieve a clean, healthy, granulating wound bed based on the principles of wound bed preparation (WBP) by removing any obstacles to healing, such as necrotic tissue, treating infection and effective management of exudate. Therefore, when faced with a patient with a wound a thorough patient assessment is essential prior to even looking at the wound.

Debridement methods

It is important to remove devitalised tissue as soon as possible to prevent infection and reduce the noxious odour that can be distressing to patients (Poston, 1996). With the aim being to remove devitalised or contaminated tissue, debris and foreign material (Collins et al., 2002), this helps to reduce the number of microbes, toxins, and other substances that inhibit healing (Fowler, 1992; Fowler & van Rijswijk, 1995; Berger, 1993). Selective and non-selective methods may be employed and it is done to optimise healing. Selective methods are accurately targeted to the area of devitalised tissue, as when scissors or scalpel might be used, to remove specific sections of tissue. Non-selective methods, as the term suggests, do not discriminate between live and dead tissue and so may have the undesired effect on healthy tissue of causing maceration and/or trauma. The most commonly employed methods are surgical (instrumental/sharp), using chemicals, mechanically and by autolysis using appropriate dressings. Frequently a combination of methods will be used over time but the method chosen will depend on the amount of necrotic tissue present in the wound bed, the extent of the wound, the patient’s medical history, and overall medical condition.

Autolysis

Collins et al. (2002) define autolysis as the body’s own natural capacity for removing necrotic tissue using its own enzymes and macrophages to lyse or break down devitalised tissue. The process can only happen within a moist, vascular environment and is dependent on a fully functioning immune system. The separation of viable from non-viable tissue is facilitated by enzymes which rehydrate and liquefy non-viable tissue much like when we use washing-up liquid to dissolve dried-on food. The application of moisture-retentive dressings artificially enhances the process and further facilitates proliferation and activity of white blood cells and growth factors (Ramundo & Wells, 2000). Hydrocolloid and film dressings and hydrogel, hydrofibre, capillary dressings (Lisle, 2002), alginate dressings covered by a moisture-retentive secondary dressing are examples of dressings that support autolysis in moist wounds. The advantage of this method is that it is generally painless but a major disadvantage is the length of time needed to achieve the desired result.

Surgical debridement

Sharp debridement or conservative sharp debridement (Figure 1), is the selective removal of loose devitalised tissue which lies above the level of viable tissue using scalpels or scissors (National Institute for Health & Clinical Excellence (NICE), 2001). It is quick, may reduce the length of hospital stay for some patients and positively influence the length of time to healing when combined with appropriate supportive measures. However, its widespread use is limited by the clinical setting, lack of expertise and the need for anaesthetic in some cases and the risk of damage to nerves, blood vessels and healthy tissue.

In the past, this was mostly performed by medical staff particularly when large areas of necrotic tissue need removing or when the patient has a serious infection associated with the wound, but, with appropriate training, is now undertaken by tissue viability nurses and podiatrists. The legal and professional issues must be carefully considered in relation to conservative sharp debridement by nurses (O’Brien, 2002). Education, skill, competence and experience must be demonstrated before any such procedures are undertaken in practice. Contraindications to this procedure include patients with bleeding conditions, vascular insufficiency, underlying malignancy and where there is uncertainty about the nature of tissue visible in the wound. The thinking behind surgical

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debridement is that the chronic wound reverts to an acute wound leading to an acute inflammatory process and ultimately, healing (Armstrong & Ruckley, 2002).

Chemical debridement

Traditionally, topical antimicrobials such as solutions of EUSOL and hydrogen peroxide were used to treat sloughy and infected wounds but were found to be toxic with prolonged use (O’Toole, 1996) and are no longer recommended for surgical wounds (NICE, 2008). The term chemical debridement can be used to include the use of silver, honey and iodine based dressings. Povidone-iodine based dressings have been used for debriding sloughy wounds but their use should be limited due to the possibility of absorption of the iodine (BNF, 2010). Dressings containing Manuka honey are currently popular as concerns increase about antibiotic resistance; their natural antibacterial, deodorising, immune system stimulation and anti-inflammatory actions cause rapid debridement (http://www.manukahoneyusa.us/FAQ.htm, n.d.) by drawing excess fluid and devitalised tissue from the wound bed by osmosis (Gethin, 2004) but the evidence of effectiveness remains sparse

Enzymatic debridement

Separation of non-viable from viable tissue is achieved by the use of fast-acting enzymes to lyse or break down necrotic tissue. The high costs, potential for instability after mixing, need for a secondary dressing and patient reports of discomfort precludes their routine use combined with the lack of evidence of effectiveness when compared with alternative, safer, more convenient methods (NICE, 2008).

Mechanical methods

Mechanical debridement methods range from the whirlpool and wet-to-dry dressings to the more sophisticated pulsed lavage and hydrosurgery. Whilst the latter could be considered to be selective, the whirlpool and wet-to-dry dressings are liable to remove viable as well as non-viable tissue; there are also concerns about cross infection and pain caused when removing the dry dressings. In the wet-to-dry method, gauze is soaked with saline and applied to the wound where it dries and adheres to the top layer of the wound bed. During removal any tissue that has adhered to the gauze is removed some of which might be viable tissue. These methods are not generally used in the UK. Hydrosurgery uses a device that creates a tight beam of sterile saline parallel to the wound causing a vacuum. The selected tissue is irrigated and debrided under pressure and any debris is irrigated from the wound. This method is complex and more commonly used in operating theatre settings. Other methods include ultrasound therapy which has been used to remove necrotic tissue and has been shown to effectively debride wounds and reduce infection caused by bacteria (Kloth & McCulloch, 1996), and topical negative pressure therapy (TNP). TNP is a non-invasive method that supports healing by removing excess exudate and slough, reducing tissue oedema, increasing local blood flow and oxygenation and promoting the formation of healthy granulation tissue (Voinchet & Magalon, 1996).

Biosurgery or larval therapy

The use of therapeutic, sterile maggots has increased substantially over the last few years to now be described as a ‘mainstream wound treatment’ (Jones, 2008) and particularly so since their inclusion on the Drug Tariff in 2004.

Despite the associated ‘yuk’ factor, there is compelling evidence both from research and anecdotally of the efficacy and cost-effectiveness of larval therapy for debridement of certain wounds (Wayman et al., 2004; Dumville et al., 2009; Jones. 2008). The larvae of Lucilia sericata (greenbottle fly) do an excellent job of debriding devitalised tissue without harming viable tissue. They secrete proteolytic enzymes on to the devitalised tissue which liquefies and is ingested by the larvae over a few days. This action destroys bacteria reducing odour and exudate as well as de-sloughing the wound. The wound pH changes and this is also thought to improve healing. They are supplied ‘loose’ or in net bags (Biofoam) and placed over the wound. During the two to five days in situ they have to be kept moist and have an oxygen supply in order to live. The larvae are supplied by Zoobiotic and need to be ordered 24 hours in advance following patient and wound assessment and the patient’s expressed, informed consent. Intended specific uses such as for malodorous, highly exuding malignant, fungating wounds should be discussed with the company nurse advisors. My personal experience highlights the importance of involving the patient in the discussion regarding the potential use of larval therapy; however, only one patient has ever shown any reluctance towards using the ‘loose’ maggots but later accepted that they would work best in her case. The main disadvantages relate to non-acceptance by staff and relatives who seem to have more of a problem accepting larval therapy than patients. There are certain precautions that need to be observed such as avoiding using them in sinuses or fistulae of unknown origin, extra care in positioning when applied to a weight-bearing part of the body e.g. sacrum or heel, or using in wounds that bleed easily or are on anti-coagulant medication.

Earlier this year a review of the VenUS II randomised controlled trial of larval therapy in leg ulcer management concluded that, although larval therapy reduced the time to debridement compared with hydrogel, it did not significantly increase the overall rate of healing. However, it should be considered where debridement is an interim goal before further treatment. It must be remembered that this trial was conducted in leg ulcer patients who have various underlying pathologies and concordance issues.

Summary

Before selecting a method of debridement consideration must be given to the aims and desired outcome of such an intervention. This requires knowledge and experience of the factors that initially led to the appearance of the devitalised tissue, the underlying patient factors, the patient’s perception, understanding and acceptance, their medical history and current medical state and how deficiencies may be corrected, the clinical setting, the history of the wound and the expertise, training and clinical competence of the practitioner.

Conclusion

Wound debridement has been described as the most important factor in wound management but not all patients with necrotic wounds will be suitable for all methods of debridement. A clear understanding of the need for debridement and the available options is necessary to make the best choice. Often debridement is not a single intervention but must be repeated using one or a combination of methods, until healthy granulation tissue becomes established in the wound bed. Surgical debridement should be reserved for the right clinical situation and only carried out by a competent practitioner under supervision until they can practise safely. Regular patient and

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wound assessment should be ongoing until the goal of healing or debridement prior to another procedure has been achieved.

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