CHAPTER 17 Wound debridement
Debridement is the removal of nonviable tissue and foreign matter from a wound and is a naturally occurring event in the wound repair process. During the inflammatory phase, neutrophils and macrophages digest and remove “used” platelets, cellular debris, and avascular injured tissue from the wound area. However, with the accumulation of significant amounts of damaged tissue, this natural process becomes overwhelmed and insufficient. Buildup of necrotic tissue then places considerable phagocytic demand on the wound coupled with the continued presence of proinflammatory cells, both of which ultimately retard wound healing (Robson, 1997; Stotts and Hunt 1997). Consequently, debridement of necrotic tissue is an essential objective of topical therapy and a critical component of optimal wound management. Debridement not only is an integral component of wound bed preparation, it also facilitates bacterial balance and moisture balance (Hopf et al, 2006; Robson et al, 2006; Steed et al, 2006; Whitney et al, 2006).
1. Reduce the bioburden of the wound. Because devitalized tissue supports the growth of bacteria, the presence of necrotic tissue places the patient at risk for wound infection and sepsis. Using external measures to remove the necrotic tissue and foreign matter reduces the volume of pathogenic microbes present in the wound.
Necrotic tissue can appear in various forms. Eschar has the firm, dry, leathery appearance of desiccated and compressed tissue layers (see Plate 24). When the tissue is kept moist, the devitalized tissue, called slough, remains soft and may be brown, yellow, or gray in appearance (see Plates 14, 25, 26A, 32). Slough may be adherent to the wound bed and edges, or loosely adherent and stringy (see Plate 25). Components of slough include fibrin, bacteria, intact leukocytes, cell debris, serous exudate, and significant quantities of deoxyribonucleic acid (DNA) (Thomas, 1990). Once the eschar is removed, slough is often visible covering the wound bed. Maintaining a moist wound environment is essential because continued exposure to air dehydrates slough, causing it to return to a hard, leathery state.
Debridement is indicated for any wound, acute or chronic, when necrotic tissue (which may be slough or eschar) or foreign bodies are present. It is also indicated when the wound is infected. Once the wound bed is clean and viable tissue is present, debridement is no longer indicated. Dry, stable (i.e., noninfected or nonfluctuant) ischemic wounds or those with dry gangrene should not be debrided until perfusion to the extremity has improved (Hopf et al, 2006; Robson et al, 2006; Steed et al, 2006; Whitney et al, 2006). Measurement of vascular status, including an ankle-brachial index, is an important component of the assessment process when considering debridement in a patient with lower leg ulceration. Debridement is also contraindicated for stable eschar covered heels. Treatment goals should be consistent with the goals and lifestyle of the individual (Hopf et al, 2006; Robson et al, 2006; Steed et al, 2006; Whitney et al, 2006).
Several methods of debridement are available for removal of devitalized tissue from necrotic wounds. Debridement methods are classified as either selective (only necrotic tissue is removed) or nonselective (viable tissue is removed along with the nonviable tissue) (Table 17-1). More specifically, debridement is classified by the actual mechanism of action: autolysis, chemical, mechanical, biologic, or sharp (conservative or surgical). Although one method of debridement may be the primary approach selected to rid the wound of necrotic tissue, debridement typically involves a combination of methods.
Conservative sharp debridement
Autolysis as a natural, highly selective painless method of debridement. Specifically, autolysis is the lysis of necrotic tissue by the body’s white blood cells and natural enzymes, which enter the wound site during the normal inflammatory process. The body’s proteolytic, fibrinolytic, and collagenolytic enzymes are released to digest the devitalized tissue present in the wound while leaving the healthy tissue intact (Rodeheaver et al, 1994). As a naturally occurring physiologic process, autolysis is stimulated by a moist, vascular environment with adequate leukocyte function and neutrophil count. Therefore, autolysis is contraindicated in patients with compromised immunity. Autolysis as a sole method of debridement is not recommended for actively infected wounds or wounds with extensive necrotic tissue or significant tunneling and undermining (NPUAP-EPUAP, 2009).
A moist environment is facilitated by the application of a moisture-retentive dressing left undisturbed for a reasonable length of time. Maintaining a moist wound environment allows the cellular structures that are essential for phagocytosis (neutrophils and macrophages) to remain intact and avoid premature destruction through desiccation. An important role of macrophages is production of growth factors, so the presence of healthy macrophages in the wound fluid supports continued production of growth factors. Once autolysis is initiated, eschar will loosen from the edges, become soft, change to a brown or gray color, and eventually transform into stringy yellow slough. It is critical to monitor the wound closely during the autolysis process because as the wound is debrided, the full wound bed and walls are exposed and the true extent of the wound is revealed; consequently, the wound will increase in length, width, and depth, necessitating a change in topical therapy. Plate 26 shows the appearance of a wound before and after autolysis.
Clinicians, patients, and family members unfamiliar with the process of autolysis can misinterpret the collection of wound exudate and the accompanying odor as indicative of an infection. It is important to emphasize that the wound exudate contains enzymes and growth factors that are essential to wound repair. In fact, wounds treated with moisture-retentive dressings are less likely to become infected than are wounds treated with conventional dressings because semiocclusive dressings are impermeable to exogenous bacteria. In addition, viable neutrophils and other natural substances in wound fluid inhibit bacterial growth (Hutchinson, 1989; Lawrence, 1994).
The use of semiocclusive dressings to create and maintain a moist wound environment launched the use of autolysis as an alternative to surgical debridement. Semiocclusive dressings trap enzyme-rich wound exudate at the wound site, which is very effective at detaching nonviable tissue from the surrounding skin and wound base. Selection of dressings that promote autolysis is based on the condition of the wound base, depth of the wound, presence of tunnels or undermining, volume of wound exudate, and the patient’s condition. When the wound base is dry, a dressing that will add moisture, such as a hydrogel, should be used. If absorption is needed, a dressing should be selected that will absorb excess exudate without dehydrating the wound surface, such as an alginate dressing for a highly exudative wound or a hydrocolloid for the minimally exudative wound. Chapter 18 provides an in-depth discussion on dressing selection to promote autolysis while matching the needs of the wound.
Debridement by autolysis compares favorably with other methods of debridement in terms of effectiveness (Konig et al, 2005). However, the process is slower than alternative methods such as mechanical and sharp. A multicenter randomized trial conducted by Burgos et al (2000) showed no significant difference in healing of Stage III pressure ulcers with the use of a hydrocolloid for autolysis compared to a commercially prepared topical enzyme product. Another randomized study comparing the same products found the enzyme to be a faster when used to treat Stage IV pressure ulcers on the heel after surgical debridement (Müller et al, 2001). The time frame for the occurrence of autolysis varies depending on the size of the wound and the amount and type of necrotic tissue. Generally, the softening and separating of necrotic tissue is observed within days. If tissue autolysis is not apparent in 1 to 2 weeks, another debridement method should be used (Hopf et al, 2006; Robson et al, 2006; Steed et al, 2006; Whitney et al, 2006).
Autolysis can be used in combination with other debridement techniques. In fact, promotion of autolysis is an important adjuvant to all debridement modalities for ongoing maintenance debridement and prevention of tissue dehydration and cellular desiccation. For example, after surgical sharp debridement of a pressure ulcer, the application of a hydrogel-impregnated gauze maintains a moist wound environment, thus preventing tissue desiccation and promoting continued softening and loosening of residual necrotic tissue. It often becomes necessary to combine dressings to achieve debridement while meeting all the needs of the patient and wound. For example, a transparent dressing is inappropriate for debridement of a wound that has depth or is heavily exudative. Instead, a dressing such as an alginate is warranted because it will fill the wound depth and absorb the exudate (see Chapter 18).
Necrotic wound tissue can be removed through a chemical process using enzymes and sodium hypochlorite (Dakin’s solution). Silver nitrate is another method of chemical debridement; however, it is more commonly used on epibole (closed or rolled wound edges) as described in Chapter 4 and shown in Plate 4 and hypergranulation (see Chapter 6 and Plate 27).
Topical application of exogenous enzymes is a selective method of debridement. Over the years, various sources have been used to manufacture enzymes (e.g., krill, crab, papaya, bovine extract, bacteria). Today the only enzyme available in the United States is collagenase, which is derived from clostridium bacteria. Collagenase digests collagen in necrotic tissue by dissolving the collagen “anchors” that secure the avascular tissue to the underlying wound bed (NPUAP-EPUAP, 2009).
Similar to autolysis, enzymatic debridement is slower than mechanical or sharp debridement but is frequently used for initial debridement when anticoagulant therapy renders surgical debridement unfeasible (Konig et al, 2005; Ramundo and Gray, 2008). The length of time required to achieve debridement may range from several days to weeks. Unlike autolysis, enzymes may also be used to debride a wound with significant bacterial bioburden or infection (Ramundo and Gray, 2008).
Specific ions, including several commonly used antimicrobial dressings and antiseptic solutions, inhibit or inactivate collagenase. Silver dressings and cadexomer iodine have been reported to reduce collagenase activity by more than 50% and 90%, respectively. pH levels below 6.0 or above 8.0 common in antiseptic cleansers containing heavy metal ions, acetic acid, and hyperchlorite also reduce the activity of collagenase.
A secondary dressing is required when an enzyme is used and should be selected based on the needs of the wound. With the previously mentioned exceptions, manufacturer’s state that most dressings can be used safely with enzymes, including gauze, hydrogels, and transparent film dressings; however, silver-impregnated dressings should be avoided. Frequency of enzyme application is at least daily and may be twice daily; therefore, the secondary dressing also should be appropriate for daily or twice-daily changes. Enzymatic debridement can be augmented by using a moisture-retentive dressing. Enzymes require a prescription, so their use has cost and reimbursement implications. In addition, daily or twice-daily dressing changes dictate considerable commitment on the part of the caregiver (patient, family, or staff) that may not always be reasonable or acceptable.
When collagenase is used on a wound with intact eschar, the eschar must be cross-hatched to allow penetration of the enzyme, and the wound surface must be kept moist. Cross-hatching the eschar is achieved by using a no. 10 blade to make several shallow slits in the eschar without damaging the viable wound base. Once the eschar begins to separate or demarcate from the surrounding skin, the enzyme can be applied to the wound edges along the line of demarcation to hasten separation. At this point, conservative sharp debridement can be used to remove softened necrotic tissue. Enzyme treatment can then be continued, or another debridement technique such as autolysis can be instituted. Because these enzymes are selective, damage to viable tissue in the wound bed should not occur if the dressing is continued once debridement is completed and viable tissue is exposed. However, enzyme application typically is discontinued when the wound bed is free of necrotic tissue. More appropriate dressings are available at a fraction of the cost and should be implemented once the wound is debrided. A transient stinging or burning sensation, particularly when the enzyme comes into contact with intact skin, has been reported (Ramundo and Gray, 2008). Barrier ointments can be used to protect the periwound skin.
Originally used as a topical disinfectant for wounds sustained in war, Dakin’s solution (diluted sodium hypochlorite solution) has a long history of being used to cleanse, debride, and control odor in wounds (Lindfors, 2004). As a debriding agent, Dakin’s solution denatures protein, therefore loosening slough and rendering it more easily removed from the wound. Collagen degradation and fibroblast migration are affected by the concentration of Dakin’s solution. Vick et al (2009) found that less than 0.5% concentration resulted in little or no collagen degradation, whereas 0.5% either partially or completely degraded collagen.
Dakin’s solution is most appropriately used in conjunction with periwound skin protection for wounds with a large amount of slough or odor. Gauze is saturated with the diluted Dakin’s solution is saturated into gauze, lightly packed into the wound, and covered with a secondary dressing. If the goal is debridement, the dressing is changed twice daily. Use of Dakin’s solution should be considered a short-term treatment (fewer than 10 days). Once infection and odor are under control and viable tissue exposed, alternative dressing and debridement techniques should be implemented.
Originating from the battlefield, maggots have been used to achieve a biologic method of debridement. Physicians noted anecdotal reports from medics who observed the rapid removal of necrotic tissue when maggots were present on the wound bed. Today, therapeutic maggot therapy involves sterilizing the eggs of Lucilia sericata (greenbottle fly). Once the eggs hatch (again, under sterile conditions), the sterile larvae are introduced into the wound bed.
It is theorized that larvae secrete proteolytic enzymes, including collagenase, allantoin, and other agents, which rapidly break down necrotic tissue (NPUAP-EPUAP, 2009). It is also believed that the larvae ingest microorganisms, which are then destroyed. Some researchers are investigating the effects of maggots on fibroblasts and extracellular matrix interaction and enhancement of healing beyond the debridement effects (Chambers et al, 2003; Horobin et al, 2003). Because of this reported action and the emergence of resistant organisms, there is renewed interest in maggot therapy in some centers, and more research supporting this therapy is available (Sherman 2002, 2003; Wallina et al, 2002; Wolff and Hansson, 2003).
Despite the renewed interest in clinical centers and reports in the literature, maggot therapy is still generally considered a last resort option when the patient is not a surgical candidate and the wound has not responded to conventional methods of debridement. A review of evidence concluded that maggot therapy offers no more overall effectiveness than other methods of debridement (Gray, 2008).
Care should be taken to prevent the larvae from coming in contact with healthy skin because the proteolytic enzymes can cause damage. Pain and bleeding have been reported, so the patient should be monitored for both, particularly with the widespread use of antiplatelet therapy (Steenvorde and van Doorn, 2008; Steenvorde et al, 2005). The main disadvantage to maggot therapy is the sensation of crawling that some patients experience, but confinement of the larvae to the wound bed decreases this sensation. Various dressings have been described; most involve periwound protection with mesh or nylon net to contain the larvae and an absorbent pad to absorb exudate (Van Veen, 2008). Biosurgical therapy should not be used with wounds that are poorly perfused, require frequent inspection, or have exposed blood vessels, necrotic bone, or limb-threatening infections (NPUAP-EPUAP, 2009).