Wound bed preparation (WBP) is a systematic approach to wound management by identifying and removing barriers to healing. The concept was originally developed in plastic surgery. It includes wound assessment, debridement, moisture balance, bacterial balance, and wound cleaning.
Conceptual frameworks
As applied to chronic wounds During the year 2000, the concept was applied to systematizing the treatment of chronic wounds. The 2000 proposals recommended that wound management address the identifiable impediments to healing in order to achieve more successful outcomes. Three publications appeared that year that focused on the concept of managing the healing processes of a wound exudate, bioburden and devitalized tissue. Initially, emphasis was placed on debridement, moisture balance and bacterial balance as the three guiding principles of good wound care, while at the same time recognizing that the provision of care includes a vast array of patient, clinical and environmental variables.
TIME acronym (Tissue, Inflammation and Infection, Moisture, Epithelial) Since the year 2000, the wound bed preparation concept has continued to improve. For example, the TIME acronym (Tissue management, Inflammation and infection control, Moisture balance, Epithelial (edge) advancement) has supported the transition of basic science to the bedside in order to exploit appropriate wound healing interventions and has not deviated from the important tenets of debridement, moisture balance, and bacterial balance. The TIME framework is not a continuum and as such is applicable to a wide range of wounds. The WBP model can be effectively applied only when a high level of precision is utilized in the assessment of the patient and their wound. The corollary of this is that intervention demands an equally high level of precision and this should be preceded by a comprehensive wound assessment.
Aspects of wounds and wound care
Wound assessment
Wound assessment is a vital first step in the precision management process. The purpose of wound assessment is: To identify:
the origin of the wound, the effects of the wound on the individual, the effects of the individual on the wound. To determine:
if healing is taking place, the most appropriate management of the wound. To gather data:
to permit a comparison of wounds and their management. Unfortunately, universal agreement as regards the precise mechanisms of how this should be accomplished is yet to be agreed.
Debridement
Debridement is an essential element of effective wound care. Although this view is deeply rooted in practice it is nonetheless based on empirical observation. Bradley et al. have stated that it is "unclear whether wound debridement is a beneficial process that expedites healing". Despite this confusing situation, current recommendation favours regular debridement. It is thought that even in an immune compromised patient debridement can assist in establishing a favourable balance of the wound bioburden.
Moisture balance Establishing a moisture balance beneficial to the wound bed is another prerequisite of care. The natural response to injury is inflammation typified by the local expression of histamine and bradykinin and leading to vasodilation of the vessels that are in relative close proximity to the site of injury. As serum based fluid moves out of the vessels into the interstitial spaces the resultant soft tissue oedema manifests on the wound surface as exudate. In the chronic wound this exudate contains a surfeit of proteolytic enzymes and other components not seen in acute wounds and these compounds have a corrosive effect on the wound bed and surrounding peri-wound skin. The application of dressings, topical negative pressure, compression garments and leg elevation/exercise have been identified as methods for management of wound exudate.
Bacterial balance All wounds are considered to harbor microorganisms. Management of the bacterial balance is of vital importance if delays in healing are to be avoided. The biological removal of micro-organisms, including potential pathogens, and tissue debris from the wound of an immune-competent patient is a wound cleansing activity that takes place almost immediately after wounding and which helps to reduce the threat of infection. However, a range of risk factors exist that increase the likelihood of infection intervening, and these include; age, depleted nutrition, down-regulation of the immune system, systemic disease, and poor tissue perfusion of oxygen. Thus, in the above circumstances or when a wound has become infected, wound cleansing activities beyond the natural biological processes are required so that the wound bioburden is maintained at a level where the host can remain in control.
Biofilms
Biofilm infection
Attaching to a surface is a natural association for bacteria in the wild. Biofilm phenotype bacteria are microbial communities that are attached to a surface and are embedded in an extracellular polymeric substance (EPS) consisting of proteins, glycoproteins, nucleic acids (RNA, DNA) and polysaccharides (slime). This mantle affords protection from antimicrobial and cellular attack. In contrast, planktonic phenotype bacteria are free-floating in nature and do not possess the defence structures afforded by the creation of the EPS slime. Within the biofilm, a rich biological diversity may be found. The attached (sessile) bacteria release proteases which help to perpetuate a chronic inflammatory state. Therefore, the potential exists for these exogenous proteases to work in tandem with endogenously produced proteases and degrade growth factors and tissue proteins that are necessary for the healing process.
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