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Snm11460 wound bed - a51. Introduction 2. The Bacterial Balance within a chronic wound 2.1 Bacterial involvement in a chronic wound and assessment 2.2 Bacterial screening of a chronic wound 2.3 Variables that affect the bacterial burden of a wound 2.4 Bacterial burden, pathogenicity and the presence of biofilms in wound healing 2.5 Antibiotics and antiseptics in wound infection 3. Management of necrosis 3.1 Surgical and sharp debridement 3.2 Enzymatic debridement 3.3 Autolytic debridement 3.4 Mechanical debridement 4. Exudate Management 4.1 Direct and indirect exudate management 4.2 Wound Dressings 5. Molecular events in wound healing cellular dysfunction 6. Molecular events in wound healing biochemical balance 7. Conclusions Vincent Falanga, MD
Professor of Dermatology and Biochemistry, Boston University School
of Medicine; Chairman of Dermatology Department And Training
Program, Roger Williams Medical Center
Rather suddenly, the term "wound bed preparation" has burst into the wound care field and is already having a tremendous impact on how we approach and think about chronic wounds. One might argue that the term itself is very simple, and some would even wonder what is new about it. Yet, there is little doubt that the focus on wound bed preparation is being successful, for it is galvanising both clinicians and industry into renewed action for the benefit of our patients. Wound bed preparation as a strategy is allowing us to break various aspects of wound care into individual components, while at the same time maintaining a global view of what we wish to achieve. In this comprehensive compendium on wound bed preparation, the various aspects needed for achieving it are discussed in detail and should provide clinicians with a very substantial working knowledge of the field. In this preface, I have the opportunity to comment on wound bed preparation, why it has become so important, and how it will evolve in the next several years. I regard wound bed preparation as the global management of the wound to accelerate endogenous healing or to facilitate the effectiveness of other therapeutic measures. Specifically, with my comments, I want to differentiate wound bed preparation from wound debridement alone, suggest the need for a more prolonged, maintenance debridement phase, and discuss the importance of eliminating wound exudate. I believe that, ultimately, wound bed preparation will also involve the correction of the wound's biological microenvironment. This may require the elimination of phenotypically abnormal cells and correction of corrupt matrix Chronic wounds have always lived in the shadow of acute wounds. Scientific breakthroughs, therapeutic measures would generally first be developed or envisioned for wounds caused by trauma, scalpel, or other types of acute injury. The whole cascade of wound-healing events for which we now have a seemingly endless number of diagrams is really an attempt to explain what happens after acute injury to the skin or, for that matter, to other organ systems. Inevitably, lessons learned about acute injury were extrapolated to the care of chronic wounds, which have often been seen as an aberration of the normal process of tissue repair. There are many examples of how this reliance on acute wounds worked out. For instance, stimulation of re-epithelialisation by dressings providing moist conditions was first observed experimentally in acute wounds.
Later, this lesson was extrapolated to the care of chronic wounds. The acceleration of healing by peptide growth factors was first formally demonstrated in experimental acute wounds in animals. These observations provided proof of principle for the effectiveness of topically applied growth factors, and led to testing and commercialisation of these agents in chronic wounds. There are many other examples, but the point is that knowledge accumulated about acute injury has been the anchor on which we have relied for developing a scientific and therapeutic strategy for chronic wounds. However, there are problems with this rather simplistic approach and, as I will explain, "wound bed preparation" is a vehicle for chronic wounds to regain their independence from models of Let us analyse how reliance on acute wounds, while helpful, has influenced the management of chronic wounds in ways that are not always realistic. For example, if one starts with the same perspective used for acute wounds, one common error is to view wound bed preparation as the same as wound debridement. In acute wounds, wound debridement is a good way to remove necrotic tissue and bacteria. After that is done, one should have a clean wound that can heal with relative ease. This is not the case for chronic wounds, where much more than debridement needs to be addressed for optimal results. For one, defining the necrotic material in chronic wounds is not so easy. Chronic wounds have what I call "necrotic burden", consisting of both necrotic tissue and exudate. Chronic wounds can be intensely inflammatory, e.g., venous ulcers, and thus produce substantial amounts of exudate that interfere with healing or with the effectiveness of therapeutic products, such as growth factors and bioengineered skin.
So, in the context of wound bed preparation, not only do we need to concern ourselves with removal of actual eschars and frankly non-viable tissue, but also with the exudative Another important aspect of chronic wounds, which makes them different from acute wounds in the context of wound bed preparation, is the possible need for a "maintenance debridement" phase. Somehow, we have always thought of debridement, whether it be done by surgical, enzymatic, or autolytic means, as a procedure or a therapeutic step with defined time frames. That may be true of acute wounds that have become colonised and necrotic, and thus need to be revitalised. However, with chronic wounds, we are generally unable to fully remove the underlying pathogenic abnormalities; necrotic material, non-viable tissue, exudate, i.e., the necrotic burden, continues to accumulate.
This notion of an initial debridement phase followed by a maintenance debridement phase is one that we should seriously study and consider adopting within the context of wound bed preparation. It might very well be that we have not paid enough attention to this problem. For example, clinicians will agree that, after initial debridement of chronic wounds, one may observe a temporary positive outcome on wound closure. However, there is often a healing arrest, with a return to a poor wound bed. One explanation is that, because of the underlying and uncorrected pathogenic abnormalities, there is continued accumulation of necrotic tissue and exudate which now cause the healing arrest. Rather than always starting from the beginning, with therefore periodic debridement and exudate control, one might consider a steady state removal of the necrotic burden that should go on throughout the life of the wound.
As already mentioned, in the context of wound bed preparation the exudative component of the "necrotic burden" is not to be underestimated. Chronic wound fluid, in contrast to fluid obtained from acute wounds, has been shown to slow down or block the proliferation of key cells, such as keratinocytes, fibroblasts, and endothelial cells.
Chronic wound fluid contains a number of metalloproteinases that can break down or corrupt essential matrix material needed for optimal movement of cells and for re- epithelialisation. Moreover, there is evidence that macromolecules present in the wound fluid and accumulating in the wound bed can bind or trap growth factors and render them unavailable to the healing process. By focusing on management of wound exudate, and not only on removal of necrotic tissue, we hope to find more effective ways to control the exudate. Also, because of the many deleterious effects of wound exudate on growth factors and matrix material, we are then beginning to place emphasis upon correcting the biological microenvironment of the wound. The biological microenvironment of chronic wounds is clearly not understood, and we might feel that for now we have limited weapons to address it properly. As we read this manual on wound bed preparation, however, we will find that many of the approaches we use to treat chronic wounds may have very beneficial effects on this more elusive component of wound bed preparation. For example, optimal compression therapy for venous ulcers will decrease the amount of exudate, and thus clear the macromolecules that may be trapping growth factors. Similarly, correction of the bacterial burden decreases the possibility of infection but also diminishes the ongoing inflammation that often characterises many chronic wounds. It has been said that some chronic wounds are "stuck" in one of the phases of the normal healing process, such as the inflammatory or proliferative phase. Eliminating the bacterial burden, by the use of debridement or slow-release antiseptics, can help this situation. As another example, appropriate debridement will remove tissue and therefore cells that have accumulated and are no longer responsive to signals required for optimal wound healing. In this respect, it has been shown that fibroblasts from chronic wounds, including venous and diabetic ulcers, have become senescent and are unresponsive to certain growth factors. I have used the term "cellular burden" for these cells. When we debride wounds, we are removing this cellular burden and restoring wound responsiveness. In time, we might develop chemical or biological means for normalising these cells, rather than Realistically, one can regard this manual on wound bed preparation as a living document. I say that because we should recognise that the field will continue to evolve, and undoubtedly new approaches for wound bed preparation and its different components will become available. However, I feel that a major hurdle has been overcome. Specifically, we are now beginning to recognise that chronic wounds have a complex life of their own, and that they are not simply an aberration of the normal healing process. The concept of wound bed preparation allows us to dissect the different components that need to be addressed in chronic wounds, and to develop long-term strategies for the more complex issues that lead to failure in healing.
1. Introduction Throughout the last decade new and innovative technologies, such as topically applied growth factors and bio-engineered skin products (see Table 1), have been at the forefront of the drive to treat chronic non-healing wounds. Unfortunately, despite these exciting and technologically advanced therapies, there remains a lack of knowledge within the medical community of wound healing, with wound bed preparation frequently underestimated. Furthermore, while standards and guidelines are available to clinicians and nurses for wound management these are either frequently not followed or only place emphasis on specific components of wound care, such as wound debridement or control of infection. Therefore, it remains critically important that clinicians provide thorough wound care, and ensure that appropriate wound bed preparation is undertaken, in order to derive the maximum benefit from today's advanced wound care products (Falanga 2000a).
Table 1. Commercial skin substitutes and growth factors/cytokine treatments currently employed in wound healing (Falanga 2000a) Growth factor/Cytokine preparations Regranex® recombinant human PDGF Leucomax® recombinant human GM-CSF Procurren Solution® platelet-derived wound healing formula (PDWHF) Skin substitutes Dermagraft® - human fibroblasts in an absorbable matrix Transcyte® - devitalised fibroblasts on a nylon mesh Biobrane® - a cellular dressing consisting of collagen bound to nylon fabric Epicel®- autologous epidermal graft Alloderm® - a cellular, allogenic dermal graft Integra®- dressing consisting of bovine collagen and chrondroitin-6-sulphate Composite Cultured Skin® - human fibroblasts and keratinocytes in a bovine collagen sponge Apligraft® – human fibroblasts and keratinocytes in a bovine collagen matrix This booklet aims to provide an explanation of the concept of wound bed preparation, and to act as a step-by-step guide on preparing the wound bed, emphasising the key elements of local wound care - bacterial balance, management of necrosis, biochemical balance, exudate management and cellular dysfunction - in order to obtain optimal healing (see algorithm in Figure 1).
Bacterial balance Figure 1. This algorithm demonstrates an approach to wound bed preparation 2. The Bacterial Balance within a chronic A major influence on wound care practice has been the clinicians' fear of wound infection. However, all chronic wounds contain bacteria, and their presence in the wound does not necessarily indicate that infection has occurred or lead to impairment of wound healing (Kerstein 1997; Dow et al 1999). Furthermore, it has also been suggested that the presence of certain bacteria within a chronic wound may actually facilitate the healing process (De Haan et al 1974; Pollack 1984). This would appear to be supported by the observation of Louis Pasteur over 100 years ago, "The germ is nothing. It is the terrain in which it is found that is everything" (Pasteur 1880). 2.1.1 Defining bacterial involvement in the wound Bacterial involvement within a wound can be divided into three categories - contamination, colonisation and infection (see Dow et al 1999; Sibbald et al 2000).
Wound contamination – is defined as the presence of non-replicating microorganisms within the wound and encompasses the majority of the microorganisms present in a Wound colonisation – is defined as the presence of replicating microorganisms adherent to the wound in the absence of injury to the host. This would include skin commensals such as Staphylococcus epidermis and Corynebacterium species, whose presence has been shown to increase the rate of wound healing (Rodeheaver Wound infection – is defined as the presence of replicating microorganisms within a wound with subsequent host injury. A pathogenic micro-organism may initially colonise a wound without inducing host injury, however as the bacterial burden increases, the colonised wound is subtlely transformed into a covert infection (Thompson and Smith 1994), which although not involving extensive tissue invasion is sufficient to inhibit wound healing. Ultimately, as the bacterial burden increases yet further, evident wound infection or systemic dissemination (sepsis) can occur (Dow et The various diagnostic approaches of screening infection within a chronic wound are described in Table 2. However, for routine assessment of the bacterial burden, semiquantitative bacteriology remains the most practical means and correlates well to the gold standard quantitative biopsy results first described by Levine et al (1976) (see Dow et al 1999). Table 2. Techniques for assessing infection in chronic wounds (Dow et al1999) Technique Description Tissue is biopsied, Evaluates for the Invasive procedure. Primarily weighed, placed in a reserved for clinical sterile tissue grinder trials and other with a known volume within tissue as research settings. Time consuming.
homogenised to free Expensive, possibly microorganisms from evaluate surface tissue matrix. The homogenate is seriallydiluted and plated. After incubation, colonies are enumerated and identified and colony counts are calculated. Swab is twirled over a 1 cm2 surface area study to define role.
of the wound and agitated in 1 mL of quantitative biopsy transport media. but less rigorously Then serially diluted colony countsobtained byquantitative biopsyby 1 log.
Swab is rolled across in specificity.
choice under most bed and inoculted practice settings. on standard media in petri dish, then wound bed results in excess presence of surface colonisers.
A rapid technique sample collection be identified. diluted 10-fold and Technique is highly operator sensitive.
closure or delayed A 0.02 mL aliquot is placed on a slide, safely performed.
heater-fixed, and stained. A single bacterium per total field corresponds may be identified.
to >105 CFU/gm of tissue. non-invasive culture quantitate technique requiring thorough irrigation technique to serve bacterial burden.
and then cultured. as an alternative to biopsy. While semi-quantitative bacteriology is a relatively quick and inexpensive diagnostic technique, and is the procedure utilised most frequently in clinics, there can be a loss of specificity (Sapico et al 1980). Furthermore, if the wound bed is inadequately prepared, the clinician may be provided with confusing or nonsignificant results (Sibbald et al There are a number of variables that should be considered by the clinician which are known to affect the bacterial burden of a wound and increase the risk of infection in a wound. These include the amount of necrotic or sloughy tissue in the wound, the number of organisms, bacterial pathogenicity and host factors. The following equation indicates that although bacterial quantity and virulence are important factors in assessing a wound for infection, host resistance is clearly of critical importance (Dow et al 1999; Sibbald et al 2000). Infection = dose x virulence "Host resistance is the single most important determinant of wound infection and must be meticulously assessed in every situation where a chronic wound fails to heal". (Dow at al 1999) Host resistance can be determined by examining any local or systemic factors that will lead to reduced wound healing in a patient.
2.3.1 Local and systemic factors that can affect host resistance Local factors relate to those local wound characteristics (such as wound size, depth and duration) that will increase the likelihood of wound infection. Table 3 lists a number of local factors that are related to an increased risk of infection in chronic wounds.
For instance a larger wound is associated with greater host impairment during wound healing and consequently, a greater risk of infection. The location of the wound over a bony prominence such as a shin and subsequent soft tissue destruction can be indicative of osteomyelitis (Dow at al 1999).
Equally important is the vascular status of the wound, as it has been shown that wounds with a reduced arterial pressure will remain unhealed (EWGCLI 1991; Carter 1993). The extent of wound perfusion is also important, as an inadequately perfused wound is unlikely to show the typical signs of inflammation. Host resistance can also be compromised by systemic factors (Table 3) such as metabolic disorders (diabetes mellitus – raised blood sugar levels may indicate local or systemic infection), underlying Table 3. Systemic factors that increase the risk of infection Vascular disease Diabetes mellitus Corticosteroid medications vascular disease or oedema, or patient malnutrition. Also, patient compliance with regard to smoking, drug and alcohol abuse can have a detrimental effect upon host resistance (Dow et al 1999).
The use of immunosuppressive drugs are also an important factor to be considered when assessing wound infection, as they may mask signs of localised or systemic sepsis (Dow et al 1999). Therefore, host monitoring is a critical feature of wound assessment and management.
It is clear that an increased bacterial load within a chronic wound can lead to reduced healing or indeed, no healing whatsoever! Experimental evidence indicates, that regardless of the type of organism, substantial impairment of healing occurs, when there is between 10 and 10 organisms per gram in a wound bed (see Dow et al 1999), although, it has also been shown that many chronic wounds with a bacterial load greater that 10 will heal without incident (Robson et al 1973). However, it is also thought that the number of organisms in a wound may not necessarily be as critical as the type and pathogenicity of the organism in the wound; for example, low numbers of Streptococcal organisms may cause problems. Furthermore, with an increased bacterial load and/or infection, there may be an increased rate of wound exudate; this will require removal so that it does not provide a focus for increased bacterial infection. In his presentation Falanga (2000b) has also suggested that the presence of sheets of soft adherent material or "bio-films" are an important element in wound infection and that more attention should be paid to their presence. These biofilms represent highly organised bacterial communities that allow individual organisms to interact socially with each other providing a means to exchange nutrients and metabolites. The biofilms represent protected foci of infection and bacterial resistance within the wound and the biofilm itself affords the bacteria protection from the effects of antimicrobial agents especially antibiotics and antiseptics (Davey and O'Toole 2000). Antibiotic resistance has developed as a result of the genetic elasticity of bacteria, which have developed enzymes that can dismantle the antibiotics either before or after entering the bacteria. Others can actively pump the antibiotics out of the cell or alter the shapes of the molecule to which the antibiotic binds. Thus, the actual or potential increase in the occurrence of bacterial resistance has become a major concern when using antibiotics for treating infections. Consequently, it has become essential to restrict the use of antibiotics to situations where they are absolutely necessary. Furthermore it is also important to use the narrowest spectrum of antibiotic possible (see Sibbald et al 2000).
Topical antiseptic agents can also be used in wounds. Although certain of these agents can display cytotoxic properties, if used correctly they maybe extremely effective antibacterial agents (see Sibbald et al 2000). Furthermore, in contrast to antibiotics, which have a more specific mode of action, and are effective against a narrower range of bacteria, antiseptic agents such as iodine (in cadexomer iodine) provide antibacterial action across three target areas – the cell membrane, cytoplasmic organelles and the bacteria's nucleic acid. This multi-target antibacterial effect suggests that bacterial resistance to such a topical agent is less likely to develop.
Whatever the antibacterial agent used, it is important to realise that without appropriate use of these antibiotic and antiseptic agents, wound bed preparation will remain inadequate and bacteria will continue to thrive in the wound and delay healing.
3. Management of necrosis Debridement of devitalised tissue is an essential mandatory step to the success of wound management (Bergstrom et al 1994), provided adequate blood supply to the wound is present. "A nidus for infection, necrotic tissue prolongs the inflammatory response, mechanically obstructs contraction and impedes re-epithelialisation" (Baharestani 1999)-without debridement the healing process cannot start. Table 4 lists the consequences of not debriding necrotic tissue. Although debridement occurs naturally within the wound, studies have indicated that if this process is accelerated, then the process of wound healing will be more rapid (Steed et al 1996). The clinician has the choice of four different methods of debridement, however, the decision to use a particular method depends upon a number of factors (Falanga 2000b; Sibbald et al 2000) (Table 5).
Table 4. Consequences of not debriding tissue (after Baharestani 1999) Establishment of an optimum substratum for bacterial growth with increased risk of infection, amputation, sepsis or death Imposition and perpetuation of metabolic load on the wound and added psychological stress Ongoing inflammation and leukocyte infiltration with delayed progression to the proliferative and remodelling phases of wound repair Compromised restoration of the structure and function of the skin Potential masking of underlying fluid collections or abscesses Inability to evaluate actual wound depth Protein losses through wound drainage Odour management Prevention of wound apposition secondary to the splinting effect of necrotic tissue Increased risk in burns for hypertrophic scarring with delayed healing and suboptimal cosmetic outcomes Table 5 . Key factors in choosing which method of debridement to use in wound repair (after Sibbald et al 2000) Tissue selectivity Surgical and sharp debridement methods are the fastest and most effective ways to remove debris and necrotic tissue. In essence, the scalpel in both these methods acts as an antimicrobial agent, decreasing the bacterial burden and removing "the cellular burden" (ie cells that have become old and senescent and so interfere with wound closure). Surgical debridement is normally performed where the need is extensive: the degree of undermining and tunnelling cannot be determined, there is widespread infection, bone and infected tissue must be removed and/or the patient is septic (Sieggreen and Makelbust 1997). Although, there are a number of advantages to surgical debridement (see Table 6) this method can also lead to a high risk of pain, bleeding (although this allows platelet release of growth factors), transient bacteraemia and damage to tendons and nerves (Baharestani 1999). Importantly, surgical debridement cannot be employed for all patients or in all settings (see Table 7). In contrast to surgical debridement, sharp debridement can be performed in the home or clinic environment. However, in patients with terminal disease, where comfort management is of greater importance, these approaches can be too aggressive. This form of debridement must be performed by an experienced, trained clinician.
Table 6. Advantages of surgical debridement (Drager and Winter 1999) Most rapid and effective technique to remove necrotic tissue, toxic debris and bacteria Local perfusion can be immediately improved Risk of infection is significantly diminished Minor bleeding after debridement leads to the release of several cytokines that have considerable influence on the initial process of wound repair Table 7. Contraindications for surgical debridement (Sibbald et al 2000) Lack of expertise in the procedure Nonhealable ulcer (ie insufficient vascular supply to permit healing) Septicaemia in the absence of systemic antibacterial coverage Medically unfit patient Patient on anticoagulants Home care setting Enzymatic debridement – relies upon the topical application of exogenous enzymes to the wound surface. These agents work synergistically with endogenous enzymes.
Sinclair and Ryan (1994) have stated that "the role of proteolytic enzymes in wound healing can no longer be seen as mere wound debridement. Rather it should be considered as a single, but important player in the wound healing orchestra". The most characterised exogenous enzyme is bacterial collagenase from Clostridium histolyticum, which displays great specificity for the major collagen types in the skin (type I and type III collagen) (Drager and Winter 1999; Jung and Winter 1998). It has been successfully used as an enzymatic debrider for over a quarter of a century and has a number of distinct advantages (Drager and Winter 1999) (see Table 8). Other enzymes such as fibrinolysin/deoxyribonuclease and papain have enjoyed limited success in comparison to bacterial collagenase. Furthermore, in addition to its unique debriding action, bacterial collagenase has been shown to enhance macrophage chemotaxis and activation within the wound itself (see Table 9). (Radice et al, 1996) (Herman and Shujath, 1999) Table 8. Advantages of enzymatic debridement with collagenase (Drager and Winter 1999) Selective removal of dead tissue Painless and bloodless Easily used in long-term care environments and in home-care Can be used in combination with sharp and mechanical debridement Enhances granulation tissue formation Attracts inflammatory cells and fibroblasts to the wound Reinforces the body's own healing mechanisms Table 9. Mode of action of enzymes used in wound debridement (Baharestani 1999) Bacterial collagenase Breaks down fibrin Acts on DNA of Relatively ineffective Degrades native collagen alone, indiscriminate Does not attract fibrin and requires urea Collagen by-products fibrinous exudate may act chemotactically on macrophages, fibroblasts and keratinocytes This occurs naturally to some extent in all wounds, where it is a highly selective process involving macrophages and endogenous proteolytic enzymes that liquify and spontaneously separate necrotic tissue and eschar from healthy tissue. Moist interactive dressings such as hydrogels, hydrocolloids etc can also provide an optimal environment for debridement by phagocytic cells and help to create an environment capable of liquifying slough and promoting tissue granulation (Kennedy et al 1997; Levenson 1996).
Mechanical debridement is a non-discriminatory method that physically removes debris from the wound. Examples of non-selective mechanical debridement include: wet-to- dry dressings, wound irrigation and whirlpool therapy.
Wet-to-dry dressings. This is the simplest form of mechanical debridement and is used to macerate eschar and induce mechanical separation once the dressing is removed from the wound bed (Jeffrey 1995). However, there are a number of detrimental effects to using wet-to-dry dressings, including increased patient dis- comfort and damage to newly formed tissue (Table 10).
Table 10. Detrimental effects of wet-to-dry mechanical debridement Increase in patient discomfort when changing dressings Damage to newly formed granulation tissue and fragile epithelial cells Potential for wound desiccation and peri-wound maceration Pressurised irrigation. This involves the use of either a high pressure or low pressure stream of water. High pressure irrigation has been shown to be effective in removing bacteria, particulate matter and necrotic debris from wounds. However, concerns exist with regards to driving bacteria further into soft tissue.
Whirlpool therapy. Another form of powered irrigation that is used to loosen and remove surface debris, bacteria, necrotic tissue and wound exudate. Although this method is suitable for necrotic wounds at the inflammatory phase, it is inappropriate for granulating wounds which have fragile endothelial and epithelial cells.
4. Exudate Management The elimination of wound exudate or fluid is an important part of wound management and wound bed preparation, yet its role still remains under emphasised (Falanga 2000a).
The best-looking wound bed will simply not heal if copious amounts of chronic wound exudate are associated with it. Furthermore, chronic wound fluid is biochemically distinct from acute wound fluid (Park et al 1998) and has been shown to consist of a biochemical milieu that is deleterious to the wound healing process. The presence of chronic wound fluid leads to the breakdown of extracellular matrix proteins and growth factors, and the inhibition of cell proliferation (Falanga et al 1994; Ennis and Meneses 2000).
Consequently, for proper wound bed preparation, it is imperative that the build-up of chronic wound fluid is managed efficiently to prevent negative biochemical implications occurring (Ennis and Meneses 2000).
For the clinician, the management of wound exudate can be performed either directly or indirectly. Direct wound exudate management involves the use of compression bandages, highly absorbent dressings (Sibbald et al 1999) or vacuum based mechanical systems (Ballard and Baxter 2000), although one of the simplest ways of wound exudate management is through the cleansing and irrigation of a chronic wound with saline or sterile water. This not only facilitates healing of the wound through removal of exudate and cellular debris, but it can also reduce the bacterial burden of the wound and a frequent cause for excess exudate.
Indirect approaches to wound exudate management focus on alleviating the underlying cause, such as extreme bacterial colonisation. It is important to remember that direct management of wound exudate using appropriate dressings will remain unsuccessful if treatment of the underlying cause is neglected (Falanga 2000a).
4 . 2 Wo u n d D r e s s i n g s
Clearly it is important for a wound dressing to protect the wound from either re-injury or re-infection. Additionally, the use of an appropriate dressing may not only remove copious amounts of wound exudate, but also may alleviate patient pain and reduce the costs associated with patient care. Clinicians now widely accept that, by maintaining a moist wound environment, wound healing can be accelerated by as much as 50% compared to a dry wound, often with an increased rate of re-epithelialisation (Geronemus and Robins 1982). Furthermore, as wound healing can be thought of as a continuum, the choice of dressing at one stage of the wound repair process is likely to influence subsequent events in the later phases of healing (Kerstein 1997). The recent recommendations proposed by the Agency for Health Care Policy and Research (AHCPR) in 1994 (Bergstrom et al 1994) which aimed at advising clinicians regarding correct wound dressing procedures, have been published by Ovington (1999). These recommendations consist of seven points and are summarised overleaf (see Sibbald et 1. It is important to use a dressing that will maintain a moist
2. Use clinical judgement to select a moist wound dressing for
the particular wound being treated
3. The dressing chosen by the clinician should be able to keep
the surrounding peri-ulcer skin dry while maintaining the
moisture within the wound
4. The wound dressing chosen should control the wound exudate
and not lead to desiccation of the wound bed: uncontrolled
exudate can lead to maceration of the surrounding skin and
lead to further deterioration of the wound
5. Dressings that are easy to apply and do not require frequent
changes decrease the amount of healthcarer time required
6. When applying the dressing, it is important to fill any cavities
within the wound to avoid impaired healing and increased
bacterial invasion (Stotts 1997): overpacking should be
avoided to prevent damage to newly formed granulation
tissue, which could delay healing; overpacking may decrease
the absorbent capacity of the dressing
7. All dressings should be monitored appropriately, but especially
those applied near the anus as they are difficult to keep intact
None of the many dressings currently available to clinicians address all the requirements contained within the recommendations, although Table 11 does provide a guide for choosing the appropriate dressing based upon the appearance of the wound (Sibbald et al 2000). Of these different categories of wound dressings those employed primarily for sloughy or exudative wounds are the foams, hydrofibres and crystalline sodium chloride gauze (Sibbald et al 2000). Other dressings are also available that maintain a moist environment for wound repair and can be used at other stages of wound bed preparation. Alginates are excellent for infected wounds and form a gel upon contact promoting moist interactive healing (Blair et al 1990; Barnett and Varley 1987). Hydrogels are most appropriate for the treatment of dry, sloughy wounds with low exudate levels, but have weak anti infective properties and require changing every 24-72 hours. Table 11. Choosing appropriate dressings (Sibbald et al 2000) Dressing category Appearance of wound bed Appearance of granulation tissue (bleeding) (healthy granulation/ 4. Calcium alginate 8. Nonadhesive film + = usually appropriate++ = appropriate+++ = highly appropriate Occlusive dressings such as hydrocolloids change their physical properties upon contact with the wound exudate to form a linked matrix gel. They are ideally suited to autolytic debridement, for mild to moderately exudating wounds (Friedman and Wu 1998), and can promote hypertrophic granulation.
Film dressings are ideally suited for the later stages of wound healing, such as granulation and epithelialisation, where there is reduced exudate. While permeable to water vapour and oxygen, they remain impermeable to water and bacteria.
5. Molecular events in wound healing - cellular dysfunction During the normal process of wound healing, a series of rapid increases in specific cell populations are responsible for preparing the wound for repair, deposition of the new extracellular matrix, and eventually complete wound closure. This orderly process of cellular control appears to be impaired in chronic wounds resulting in a failure to complete the repair process. For example, wounds such as venous ulcers and leg ulcers, are characterised by the defective remodelling of the extracellular matrix, a failure to re-epithelialise and prolonged inflammation (Hasan et al 1997; Agren et al 1999; Cook et al 2000). Falanga (2000b) has recently demonstrated that the epidermis in chronic wounds (such as venous ulcers) fails to migrate across the wound tissue, and that there is widespread hyperproliferation associated with the chronic-wound margins. It is believed that it is this hyperproliferation that interferes with normal cellular migration over the wound bed and results from the inhibition of apoptosis, or normal programmed cell death, within the fibroblast and keratinocyte cell populations (Falanga 2000b). Other researchers have also described several phenotypic abnormalities associated with fibroblasts from chronic wounds, including an altered morphology and a reduced rate of proliferation (Stanley et al 1997; Cook et al 2000). Fibroblasts obtained from chronic ulcers and cultured in vitro, also showed a decreased response to an exogenous application of growth factors such as PGDF-β and TGF-β (Hasan et al 1997; Agren et al 1999). Thisreduction in response is thought to be due to the fact that the fibroblasts from chronic wounds are senescent and may indicate in vivo ageing (Mendez et al 1998; Vande Berg et al 1998). It may also explain why topical application of growth factors to a chronic wound does not always lead to wound closure (Falanga 2000b). 6. Molecular events in wound healing - biochemical balance Chronic wounds are "stuck" at a particular phase of the healing process (e.g. venous and diabetic ulcers, are believed to be stuck in the inflammatory and proliferative phases respectively [Falanga 2000b]). Understanding the physiological processes involved in wound healing is essential for the clinician, but it has become apparent that it is equally important for clinicians to be aware of the molecular events that are intrinsic to the wound healing process and in particular the events in a chronic wound. In acute wounds the expression of molecules such as fibronectin and thrombospondin (and other extracellular matrix molecules) follow a defined temporal course of expression.
However, it has been shown that within chronic wounds there appears to be an abnormal over-expression of these extracellular matrix molecules. This is believed to result from cellular dysfunction and disregulation within the wound and may also have important biological implications (Falanga 2000b). Furthermore, whilst a wound bed may be visually excellent, on biopsy, numerous proteinaceous molecules are present which emanate from the circulatory system. Fibrinogen and fibrin are two molecules commonly observed histochemically in chronic wounds, particularly venous ulcers. Falanga (2000b) has recently hypothesised that the presence of these, and other, extravasated macromolecules (such as a2 macroglobulin) act as scavengers for growth factors and certain signal molecules that promote wound repair. Hence, whilst there may be abundant growth factors within the wound, they become trapped or sequestered, and consequently no longer available to the repair process, because the wound bed has been inadequately prepared. In this regard, use of compression bandaging helps to remove the wound fluid containing the fibrin and fibrinogen, thereby releasing the growth factors that can then promote an angiogenic response leading to complete wound closure (Falanga 2000b).
Therefore, it is becoming increasingly clear that to ensure wound healing progresses it is vital that the correct biochemical balance is maintained within the wound, and this can only be achieved through correct wound bed preparation.
7. Conclusions Wound treatment has advanced rapidly over the last 20 years, and coupled with the current rate of progress in treatment technology and our increased understanding of the biology of chronic non-healing wounds, this advancement is likely to continue.
However, if clinicians and (ultimately) their patients are to derive maximum benefits from these evolving therapies and technologies, a greater understanding of the basics of good wound care is essential. In the rush to utilise newer wound treatments, clinicians have often neglected the basics of good wound care. It is simple – unless the wound bed has been prepared properly, futuristic therapies such as bioengineered skin, recombinant growth factors and gene therapy techniques, (all designed to improve wound healing), will not succeed. Consequently, it is becoming apparent that guidelines focusing upon proper wound bed preparation are required to ensure effective wound care. These guidelines should provide a systematic approach to wound bed preparation and focus collectively, not individually, upon the critical components of wound bed preparation including debridement, bacterial balance in the wound, and proper wound exudate management. They should also emphasise the importance of understanding the biochemistry of wound repair and the role of the various cell populations in wound Ultimately, the aim of wound bed preparation is rapid wound healing with the formation of good quality granulation tissue that will lead to complete closure naturally or through the use of technologically advanced skin products or grafting. Only after appropriate wound bed preparation will clinicians achieve the success that they have strived for when using advanced therapies in healing wounds. APPENDIX 1. THE WOUND
Wound healing is a dynamic, natural and efficient process, that involves a Fibrin. platelets Capillaries and epithelium complex series of cellular and biochemical events, which act upon the damaged tissues – blood vessels, dermis and epidermis. Although the biological mechanisms associated with wound healing are complicated and still remain unclear, the entire process Figure 2. The process of wound healing can be divided into different phases The phases of wound healing and the factors involved During coagulation platelets liberate a number of soluble mediators, including platelet-derived growth factor, which initiate the wound healing process Coagulation is followed by an early inflammatory phase that is characterised by vasodilation, increased capillary permeability, complementactivation and polymorphonuclear leucocytes (PMN) and macrophagemigration to the wound PMNs predominate during the first days of post-wound occurrence with macrophages becoming the predominant inflammatory cell within 3 days Macrophages play a key role in regulating the subsequent events in the wound healing process by attracting further macrophages and inducingthe proliferation of fibroblasts and endothelial cells which, with increasingnumbers, form granulation tissue around 5 days post-injury and heraldthe proliferative phase Fibroblasts synthesise collagen and other extracellular matrix molecules to support new cells and the fragile capillary buds, which appear duringangiogenesis. The endothelial buds increase in vascularity, in response tothe large metabolic demand of the repair tissue). Epithelialisationrequires the migration of epithelial cells across the granulation tissue toclose the epidermal defect Collagen synthesis continues after wound closure, but also undergoes continual lysis, so a delicate balance exists between the two processes:the final remodelling phase of the wound is accompanied by increasingtensile strength and decreasing cellularity In healthy individuals, where there are no deleterious factors present, this whole process takes about 21 days and does not normally require further clinical intervention. However, in chronic wounds the orderly sequence of events observed during the normal repair process becomes disrupted or "obstructed" at one or more of the different stages of wound healing.
For the normal repair process to resume it is critical that any "barrier" is removed through correct wound bed preparation and that the healing process reverts back to an orderly series of events (Sibbald et al 2000). To a high degree, wound healing is determined by the general health of the patient.
Therefore, prior to the management of a chronic wound, the clinician should conduct a holistic assessment of the patient and a diagnosis of the wound.
2.1 Provision of an adequate blood supply to the wound
An important consideration when beginning to manage a wound is to ensure that the wound has an adequate blood supply as this will ensure that the process of healing can be fully facilitated (Kerstein 1997; Sibbald et al 2000). It is essential that patients with arterial disease be diagnosed at the outset of treatment – particularly patients with wounds on the lower extremities or with a metabolic disorder such as diabetes mellitus (Kerstein 1997; Sibbald et al 2000). A wound with a poor blood supply will be paler in comparison to the healthy granulation tissue observed in a well-perfused one. Without adequate wound perfusion, there will be insufficient nutrients and oxygen delivery, both of which are essential to support the large metabolic demand associated with the wound repair process. Furthermore, delivery of the cellular components of the immune system (such as leukocytes and macrophages), which are critical for healing to progress, is also impaired. Finally, an impaired venous blood supply cannot facilitate the removal of debris from the wound during the healing process (Kerstein 1997).
A variety of systemic and local factors, diseases, and medications may interfere with wound healing (see review by Cohen et al 1992) (Table 12). Consequently, it is crucial for proper wound management to treat the underlying causes (Kerstein 1997; Sibbald et al 2000; Falanga 2000b).
2.2.1 Nutrition Malnutrition in a patient can be a key factor in wound healing. In particular protein and vitamin deficiency may deprive the body of essential nutrients required for healing (Kerstein 1997; Jung and Winter 1998; Sibbald et al 2000). Protein is essential for the formation of new granulation tissue and severe protein malnutrition results in a decreased rate of wound healing, decreased immunocompetence and increased susceptibility to infection (Mazzotta 1994). In the USA, it is recommended that the daily allowance of protein should be increased from 2.0 to 4.0 g/kg/day during wound healing as opposed to the 0.8 g/kg/day recommendation for healthy individuals (Mazzotta 1994). Protein deficiency in patients is normally measured by their serum albumin concentration and, although figures vary, an albumin concentration of below 3.0 g/L will delay wound healing (Mazzotta 1994; Sibbald et al 2000). Table 12. Systemic and local factors that can interfere with the process of wound repair Systemic Factors – Protein deficiency Wound biochemistry – Vitamin deficiency (A, C and E) Cellular dysfunction – Mineral deficiency (zinc and iron) Compromised circulation Impaired coagulation Immunosuppressive therapy Vitamin deficiency, especially of vitamins A and C also impedes wound healing. Vitamin A is important for each stage of wound repair and a deficiency can lead to a reduction in the extracellular molecule fibronectin which in turn results in decreased cell chemotaxis, cell adhesion and epithelialisation. Vitamin C is also important, with poor wound healing being one of the symptoms of scurvy, whilst deficiency of vitamin C can lead to the breakdown of already healed wounds (Mazzotta 1994).
Minerals such as zinc and iron also play a pivotal role in the promotion of wound repair. Zinc deficiency can lead to delayed wound and ulcer closure, it may also result in a reduction in the number of lymphocytes and an increased susceptibility to recurring infection and hence poor wound healing. Iron is required as a cofactor for the enzymes involved in DNA synthesis which is critical for cell division. Consequently, iron deficiency inhibits cellular proliferation especially of the cells involved in wound debridement and healing (Mazzotta 1994).
2.2.2 The medical history of the patient and their medication Recording the patient's general medical history and monitoring their ongoing medication is also critically important for successful wound management. The presence of a major illness or systemic disease can result in the inhibition of wound healing. Autoimmune diseases such as rheumatoid arthritis or systemic lupus, and the systemic steroids and immunosuppressive agents used to control the underlying disease, can interfere with wound healing (Kerstein 1997; Sibbald et al 2000). The interference of immunosuppression with wound management has become an increasingly common problem and particularly in patients diagnosed with HIV (Kerstein 1997).
Therefore, before wound management can be instigated in autoimmune patients, the heightened immune response in these patients must be reduced to ensure wound repair can progress (Sibbald et al 2000).
Treatment with glucocorticoids results in decreased collagen synthesis and a delay in re-epithelialisation in dermal wounds (Jung and Winter 1998). Impaired coagulation (due either to the patient's genetic disposition, or the use of anticoagulants such as heparin and warfarin) will have a negative impact on the earliest stage of wound healing (Kerstein 1997). Furthermore, metabolic diseases including diabetes mellitus may also lead to an increased incidence of infection following surgery and may increase the time to complete wound healing (Mekkes and Westerhof 1995; Levin 1993; DCCTRG 1993).
2.3 Wound assessment
Inherent to effective wound management is the careful and consistent documentation of the wound itself which will enable the clinician to select the appropriate treatment modalities and evaluate the progress of the patient (see Figure 3 for an example of a wound assessment model). The wound examination includes recording the history, location, depth and dimensions of the Figure 3. Wound assessment model (after Kerstein 1997) wound, evaluation of the wound bed and the surrounding skin, and an analysis of the wound exudate and associated pain (Kerstein 1997; Sibbald et al 2000).
2.3.1 Wound history It is important for the clinician to obtain information relating to the duration of the chronic wound, any previous therapy employed to treat the wound, and if it is a recurrent wound.
The clinician can use such information to address issues concerned with preventing infection, or to assess whether there are systemic or local factors obstructing the healing process.
This information is also important if the patient is referred and another clinician becomes responsible for their treatment, as this would help to prevent the repetition of a previous treatment and also to assist in understanding if a previous diagnosis and treatment were 2.3.2 Wound location and dimensions The precise anatomical location of the wound on the patient should be recorded (Kerstein 1997; Sibbald et al 2000). This will enable the clinician to assess the time required for the particular wound to heal and completely close – a wound with an ample blood supply will heal more rapidly than a wound in a peripheral area of the body – which may have a reduced blood supply. It is also important to remember that the rate of wound healing can be affected by skin adherence; for example, a shin wound will be slower to heal than other wounds because the skin is so tightly adhered to the shin (Kerstein 1997).
The depth and area covered by a wound can also profoundly influence the rate of wound repair, thus, it is important that the depth of the wound is accurately assessed before proceeding with wound management. The wound should be checked for the presence of bone, sinuses or undermining tissue (Kerstein 1997; Sibbald et al 2000).
2.3.3 Condition of the wound bed and characteristics of wound exudate The condition of the wound bed can indicate how healing within the wound is progressing and also how effective the treatment has been (see Sibbald at al 2000). The presence of black eschar is representative of necrotic devitalised tissue and may be soft or firm. If the intention is to heal the wound then for healing to continue it is essential that this necrotic tissue is removed.
A yellow fibrous wound bed can be firm or soft. A firm base indicates that there are structures such as fascia, subcutaneous fat or a fibrin base for the future development of granulation tissue, and does not need to be removed. The presence of soft, sloughy, material may indicate the presence of infection or degraded fibrin that will require removal for healing to progress (Sibbald at al 2000).
The appearance of firm, moist granulation tissue, which is salmon red-pink in colour, is a clear indicator that the treatment regimen employed by the clinician has been effective and healing is progressing normally. Newly formed epithelialised tissue, pink-purple in colour, normally appears after this stage, usually at the edges of the wound (Sibbald et al 2000).
When assessing wound exudate clinicians usually describe it based upon quantity, characteristics and odour (see Table 13). Even if the exudate is clear the presence of a heavy exudate indicates uncontrolled oedema or an increased bacterial burden or possible infection within the wound (Sibbald et al 2000). Table 13. Classification of the exudate in chronic wounds (Sibbald et al 2000) Descriptions of chronic wound exudate Exudate quantity – described as scant, moderate or copious Exudate characteristics – described as serous-serum, sanguinous-blood, purulent-infection, or a combination of these Exudate odour – presence or absence 2.3.4 The wound margin and surrounding skin It is important for the clinician to also focus upon the wound margin in order to monitor the patient for signs of erythema, oedema, pain, or maceration of the surrounding skin. The presence of erythema, swelling and pain can indicate inflammation and infection, or unrelieved pressure, or adverse reactions to wound care treatments (van Rijswijk 1996; Sibbald et al 2000). The presence of skin maceration can be the result of prolonged exposure of the skin to wound exudate indicating that the wound dressing is inappropriate, or not being changed frequently enough, thereby keeping the wound overly moist.
It is also important to avoid exposure of the wound to allergens as chronic wounds provide optimal penetration for these substances and their systemic processing by the immune system (Sibbald et al 2000). 2.3.5 Assessment of wound pain Wound pain can serve as an important indicator of inadequate wound management.
Therefore, pain should be quantitatively assessed and routinely documented, preferably using the visual analogue scale (0 = no pain, 10 = worst pain). Chronic wound pain can be divided into incident pain, recurrent episodic pain, and continuous pain (Krasner 1997). Incident pain results from debridement or trauma to the wound, and can be relieved through the use of analgesia based upon the WHO pain ladder (Ferris et al 2001). Recurrent episodic pain is frequently experienced by the patient when their wound dressings are changed. In such cases, appropriate pain control (administered either locally or systemically) should be initiated prior to the dressing changes. Continuous pain may indicate that the underlying cause of the wound has remained untreated, or that the wound has become extensively infected. It is essential for the clinician to determine whether or not the continuous pain experienced by the patient originates from the local wound or the surrounding tissue (Sibbald et al 2000).
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