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 proposalsCherry GW, Harding KG, Ryan TJ. Wound Bed Preparation. International Congress and Symposium Series 250. London, UK: Royal Society of Medicine Press Ltd, 2000. 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.
Biofilm management We are developing greater insight into the association between delayed healing and the presence of biofilm.Percival SL, Dowd SE. The Microbiology of Wounds. In: S.L. Percival KFC, editor. The Microbiology of Wounds. New York: CRC Press, Taylor & Francis Group LLC, 2010. The relationship between delayed healing and the need for debridement is also being acknowledged. It has been suggested that the presence of wound slough provides an indication of biofilm presence,Cutting KF, Wolcott R, Dowd SE, Percival SL. Biofilms and significance to wound healing. In: S. L. Percival KFC, editor. The microbiology of wounds. Boca Raton, FL, USA: CRC Press, Taylor and Francis Group 2010. therefore, indicating the need to reduce the wound bioburden.
Methods of effectively managing wound biofilms have been reported and include the use of topical agents, systemic antibiotics and regular episodes of debridement.
Despite these advances it has been recognised that indiscriminate and widespread use of antibiotics both inside and outside of medicine is playing a substantial role in the emergence of bacterial resistance.
On a more positive note, antiseptics have been reported to possess a clear cut role in the control of wound bioburden where there are indications or risk of infection.
Wound cleansing and excision
Wound cleansing is a fundamental component of wound care. It consists of the removal of foreign matter, dead (devitalized) tissue and other physical impedimenta to healing, such as ragged edges. Despite the move in the 21st century toward evidence-based practice, the only general consensus that exists here is that cleansing and excision reduce infection rates. The recommendation has been made that cleansing is required when:
excess exudate is delaying healing, infected exudate is present, there is contamination by a foreign body including dirt and bacteria devitalised tissue (slough and necrosis) is present.
Wound cleansing is often undertaken as a ritual exercise rather than as an evidence-based activity. However, it has a role to play in all four domains of the WBP model. Wounds that are 'clean' and progressing do not require extraneous cleansing.
Criteria for a cleansing agent Wound cleansing forms an integral part of wound management and generally suggests the application of a fluid to aid the removal of surface contaminants, bacteria, and debris from the wound surface and surrounding skin.Rodeheaver GT, Ratliff CR. Wound Cleansing, Wound Irrigation, Wound Disinfection. In: D.I. Krasner GTR, R.G. Sibbald, editor. Chronic Wound Care: A Clinical Source Book for Healthcare Professionals. Malvern, P.A.: HMP Communications, 2007. Water as a cleansing agent, especially in chronic wounds has been proposed and is widely used especially in the management of infected wounds. Despite the plethora of work focussing on the value of water/saline in wound cleansing there is no current consensus as to whether water has an active role to play in the promotion of healing.
With this unclear position in mind, alternative cleansing agents such as antiseptics that possess the potential to improve clinical outcomes should be considered.
The use of antiseptics on open wounds is justified in terms of prevention/treatment of infection and improved healing outcomes.
Criteria by which a wound cleansing agent could be deemed suitable for use on wounds include: non-toxic to mammalian cells broad spectrum in action reduction of wound bioburden maintaining optimal moist wound environment easy to apply manages wound pain and malodor does not cause pain on application compatible with a variety of available wound dressings
There is a scant evidential provision in respect of guidance as to the optimal wound cleanser. In general, recommendations for practice are based on consensus opinion often derived from clinical experience and in vitro and/or in vivo studies.
Specific agents
Polyhexamethylene biguanide (polyhexanide, PHMB)
Polyhexamethylene biguanide hydrochloride is a fast-acting, broad-spectrum synthetic compound that binds to the cell envelope of both Gram-positive and Gram-negative bacteria, disrupting the bacterial cell membrane and enabling seepage of ions. PHMB has a long history of use as a contact lens cleanser, mouthwash and more recently in wound care.
It is regarded as being quite safe to use as it has been incorporated as a preservative in cosmetics. A retrospective analysis of wound cleanser clinical efficacy and cost-effectiveness focused on polyhexamethylene biguanide solution, Ringer's solution or saline in 112 venous leg ulcer patients. The study group received the polyhexamethylene biguanide solution (n=59) and the control group received either Ringer's solution or saline (n=53). In both arms, ulcer healing patterns were evaluated. Within the first 3 months of treatment, a shorter time to healing was recorded in the study group when compared with the control group - 60% v. 28% with corresponding mean time to healing being 3.31 months (study group) compared to 4.42 months (control group) p= <0.0001. More patients in the polyhexamethylene biguanide group healed in the 6-month period when compared with the controls - 97% v. 89%. The authors concluded that optimization of the local wound environment was significantly influenced through cleansing with polyhexanide solution.