Wound Bed Preparation: The Science Behind the Removal of Barriers to Healing

Wound Debridement

Clinically, debridement has been used for many years to enhance wound closure. Steed and co-workers^[40,41] have earlier highlighted its significance. The 1996 study compared rates of healing in patients with diabetic foot ulcers whose wounds were debrided using either topically applied growth factors (PDGF) alone or in combination with sharp debridement. The results showed that a lower rate of healing was observed in those centers that performed less frequent debridement. The authors concluded that debridement is a vital adjunct to topically applied growth factor therapy in the care of patients with chronic wounds.

Removal of necrotic tissue by debridement is beneficial for a number of reasons. Debridement removes dead, devitalized, or contaminated tissue, and any foreign material from a wound, which helps to reduce the number of microbes, toxins, and other substances that inhibit healing.^[42,43,44] Foreign bodies, including soft necrotic tissue, bone fascia, nonviable muscle, and ligaments, have been shown to reduce host immune defenses and encourage active infection.^[45,46]

There are five main methods of debridement: surgical or sharp, autolytic, enzymatic, mechanical, and biosurgery. The choice of debridement method will depend upon many factors, including the size, position, and type of wound, efficiency and selectivity of debridement method, pain management, exudate levels, risk of infection, and the cost of the procedure.^[32] In some cases, it may be appropriate to use more than one method of debridement.

Surgical Debridement

Surgical or sharp debridement is not a new technique, and historical texts show that ancient civilizations often made surgical changes to the wound bed.^[47] Surgical debridement is the fastest way to remove dead tissue. It causes considerable pain, and hence, it was earlier restricted to the treatment of neuropathic diabetic ulcers where the use of anesthesia and pain management was not necessary. However, this problem could be overcome with the use of topically applied local anesthetics (e.g., combination of lidocaine [lignocaine] and prilocaine), applied 30 to 45 minutes prior to debridement.^[48] Although surgical debridement is thought to be selective, there may be some damage to viable tissue, and bleeding is likely. Nevertheless, this may help to revitalize the wound and encourage healing by inundating the wound bed with growth factors and cytokines. Mild to moderate bleeding could be controlled by the application of pressure and a hemostatic calcium alginate dressing.

Autolytic Debridement

All wounds experience some level of autolytic debridement, which is the natural and highly selective process by which endogenous proteolytic enzymes break down necrotic tissue. These endogenous enzymes are mainly produced by neutrophils and include elastase, collagenase, myeloperoxidase, acid hydrolase, and lysosomal enzymes.^[49]

Autolytic debridement may not take place fast enough to encourage rapid wound healing and closure, but the use of occlusive dressings can enhance this natural process, while maintaining a moist wound bed and managing excess exudate.^[50] This allows painless, selective debridement and promotes the formation of healthy granulation tissue.^[51]

Autolytic debridement can result in the production of significant quantities of exudate. Typical practice for autolytic debridement involves the use of a hydrogel to soften and break down necrotic tissue covered with an absorptive, occlusive dressing to absorb the excess exudate.

With an increase in antibiotic-resistant pathogens, there has been a renaissance in recent times in the use of honey for the treatment of wounds and ulcers.^[52] As well as having an antibacterial action, honey provides rapid autolytic debridement and deodorizes wounds, in addition to having anti-inflammatory properties^[53] and stimulating immune responses.^[54] Though the exact mode of action remains unclear, Tonks, et al.,^[55] observed that reactive oxygen intermediate production was significantly decreased (p < 0.001), and TNF-a release was significantly enhanced (p < 0.001) by pasture honey and manuka honey.

Although on practical grounds, autolytic debridement is the easiest method of debriding wounds, it usually takes a prolonged period of time to achieve complete removal of necrotic tissue.

Enzymatic Debridement

Enzymatic debridement is a highly selective method of wound debridement that uses naturally occurring proteolytic enzymes that are manufactured by the pharmaceutical and healthcare industry specifically for wound debridement. These exogenously applied enzymes work alongside the endogenous enzymes in the wound. Several enzyme debriding agents have been developed including bacterial collagenase, papain/urea, fibrinolysin/DNAse, trypsin, streptokinase-streptodornase combination, and subtilisin. Only the first three products are widely available commercially in those markets where they are registered, although availability varies geographically.

Collagenase-based debridement. Collagenase, derived from Clostridium histolyticum, is the best characterized of all of the enzyme debriding agents. It specifically digests all triple helical collagen and will not degrade any other proteins lacking the triple helix. This is a unique feature of bacterial collagenase, since none of the other available proteases can digest collagen.^[56] It has been used for over 25 years and has a number of clinical advantages, including selectively removing dead tissue, being painless, and causing the least amount of blood loss.^[57] This type of debridement can be appropriate to use in long-term care facilities and in the home care setting.^[58] Clinical research has shown that bacterial collagenase is an effective and selective enzyme debriding agent in a range of wound types.^{[59,60,61,62,63,64,65]}

Papain-based debridement. Papain is a nonspecific proteolytic enzyme derived from the fruit of the papaw tree (Carica papaya). Papain breaks down fibrinous material in necrotic tissue and requires the presence of sulfhydryl groups, such as cysteine, for its activity. It does not digest collagen,^[66] and it requires specific activators that are present in necrotic tissue in order to be stimulated. Urea is combined with papain because urea is able to expose the activators of papain in necrotic tissue. Urea also denatures proteins, making them more susceptible to proteolysis by papain. The combination of papain and urea is approximately twice as effective at digesting protein compared with papain alone.^[67] Papain use is known to produce an inflammatory response and possibly as a result of this, considerable pain is often experienced with the use of this method.^[68,69] Therefore, chlorophyllin, an anti-agglutinin, has been added to preparations of papain/urea in an attempt to reduce the pain.^[70,71] Current preparations containing the above combination tend to cause less pain. Papain/urea preparations, however, may be particularly useful in patients with pressure ulcers combined with a loss of sensation (e.g., spinal injuries), as pain may not be a limiting factor for its use in such instances.^[33]

Mechanical Debridement

Mechanical debridement is a nonselective, physical method of removing necrotic tissue and debris from a wound using mechanical force. This debridement method is generally easy to perform and is more rapid than autolytic and enzymatic debridement. However, this nonselective method can damage healthy granulation tissue both in the wound bed and at the margins of the wound thus causing significant discomfort to the patient. Despite these disadvantages, there are a number of mechanical debridement methods that are in use.

Wet-to-dry dressings are the simplest method of mechanical debridement, but due to the frequent dressing changes, it can require considerable nursing time and hence is costly.^[72] Wet gauze dressings are placed onto the wound bed and allowed to dry, trapping the necrotic debris within the gauze. Upon removal of the dressing, embedded necrotic tissue and debris are mechanically separated from the wound bed.^[73] Pressurized irrigation involves applying streams of water, delivered at either high or low pressure, to wash away bacteria, foreign matter, and necrotic tissue from the wound. However, if the pressure is too great, there may be a risk of forcing bacteria and debris deeper into the wound or damaging viable tissue.^[74] Whirlpool therapy uses powered irrigation and can be very effective at loosening and removing surface wound debris, bacteria, necrotic tissue, and exudate from the wound. Ultrasound treatment has been used to remove necrotic tissue and has been shown to effectively debride wounds and reduce infection caused by bacteria.^[75] Vacuum-assisted closure is a noninvasive form of mechanical or physical debridement that exposes the wound bed to negative pressure (approximately 125mmHg below ambient pressure) by way of a closed system. It helps healing of chronic wounds by minimizing exudate and slough in the wound bed, reducing tissue edema,^[76,77] increasing peripheral blood flow, improving local oxygenation, and promoting angiogenesis and good quality granulation tissue.^[78]

Biosurgery (Myiasis)

For a decade since its introduction in 1931, fly maggots have been known to help debride and heal wounds. This technique uses sterile maggots, which digest sloughy and necrotic material from the wound without damaging the surrounding healthy tissue.^[37] In the study by Mumcuoglu, et al.,^[79] complete debridement was achieved using maggots in 38 of the 43 patients (88%) with chronic leg ulcers and pressure ulcers. Among them, five patients had their limbs salvaged after being referred for amputation of the leg. Likewise, Sherman^[80] in a cohort of 103 patients with pressure ulcers observed that 80 percent of maggot-treated wounds were completely debrided compared to only 48 percent of wounds that were treated by conventional therapy alone (p = 0.021). The precise mechanism by which maggots debride the wound and promote wound healing remains unclear. However, there is speculation that they probably act by ingesting and killing bacteria, exerting a bacteriostatic effect by increasing wound pH,^[81] secreting proteolytic enzymes that are important in eschar degradation,^[82] and increasing tissue oxygenation.^[83] Nevertheless, despite recent encouraging reports,^[80] some patients complain of increased pain with maggot therapy.^[84] Likewise, the potential psychological and aesthetic considerations cannot be ignored.

Wounds. 2003;15(7) © 2003  Health Management Publications, Inc.

Cite this: Wound Bed Preparation: The Science Behind the Removal of Barriers to Healing - Medscape - Jul 01, 2003.