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injury and lasts between 4 days and 2 weeks. Re-epithelialisation involves the migration of epithelial cells from the wound margins and other nearby skin appendages. The purpose of this process is to cover the wound and re-establish an intact epithelial barrier. Angiogenesis is stimulated by the low oxygen tension and high lactate levels typical of underperfused wound tissues. New vessels form under the influence of angiogenic growth factors and matrix metalloproteinases degrade the extracellular matrix to facilitate passage of these vessels. Once vascularisation is improved and the oxygen tension increases, the angiogenic stimulus is switched off and apoptosis occurs. Fibroblasts migrate into the wound to supplement the provisional wound matrix by the secretion of proteoglycans, glycosaminoglycans, collagen and other proteins. A number of fibroblasts Table 1.1. The process of wound healing. Phase Cellular and biophysiological events Haemostasis Vasoconstriction Platelet aggregation, degranulation, fibrin thrombus formation Inflammation Neutrophil migration Monocyte migration and differentiation into macrophage Lymphocyte infiltration Proliferation Re-epithelialisation Angiogenesis Collagen synthesis Extracellular matrix formation Remodelling Collagen remodeling Vascular maturation and regression Source: Guo and Dipietro, 2010. 8 Textbook of Plastic and Reconstructive Surgery will be stimulated to differentiate into myofibroblasts, thus causing wound contraction, an essential process that reduces the size of the wound. The remodelling phase is the longest phase of wound healing, lasting up to a year after the injury. Collagen is synthesised for about 5 weeks, initially in a disorganised fashion, and predominantly consisting of type III collagen. Continued turnover produces stronger type I collagen, the fibrils of which are laid down in a more organised arrangement affording greater strength. At 1 week, the wound has 3% of normal breaking strength, at 3 weeks 30% and at approximately 3 months after injury, strength peaks at 70–80%. 4. WOUND MANAGEMENT The fundamental principles of wound healing are essential in reconstructive surgery, regardless of the procedure being conducted. These principles are: Comprehensive debridement of the wound Diligent infection control Provision of an adequate blood supply. From a clinical perspective, wounds can heal in three ways: Primary intention – skin edges are directly opposed and good healing occurs with minimal scar formation. Secondary intention – the wound is left open and closes naturally, usually via a combination of contraction and epithelialisation. Delayed primary intention – the wound is left open for some time and then closed if it is found to be clean. This is usually used when closing badly contaminated wounds to enable drainage of infected material. Management of wounds involves at the first stage a comprehensive assessment of both the patient as a whole and the wound itself. Assessment of the patient should include a general health screen, focusing particularly on the conditions and factors known to affect wound healing (see Table 1.2). In plastic surgery, numerous wound assessment tools are used in different units. The DIME (Debridement, Infection/ Inflammation, Moisture balance, Edge of wound) model is one such tool, and is very useful in assessing prognostic characteristics of wounds and assisting in the selection of suitable interventions such as dressings. 4.1. Debridement This assesses the need to remove any unwanted material from the wound. Unwanted material may include necrotic or dead tissue, biofilms, senescent cells, foreign bodies or non-viable tissue (slough or Principles of Reconstructive Surgery 9 eschar). Slough usually has the appearance of grey or yellow, soft or stringy material, whereas eschar is thick, leathery and either black or brown. Unwanted material within the wound is undesirable as it (1) impedes wound healing by harbouring infection; (2) prevents healing from progressing past the inflammatory phase; and (3) prevents wound contraction and re-epithelialisation. There are five ways to debride wounds: 1. Autolytic 2. Mechanical 3. Enzymatic 4. Surgical/excisional 5. Biological/maggot. Autolytic debridement occurs when macrophages and proteolytic enzymes cause separation and liquefaction of non-viable tissue. Autolytic debridement can occur naturally or be produced by dressings such as hydrogels, occlusive/semi-occlusive dressings (e.g. film/transparent dressings) or hydrocolloids. Mechanical debridement uses physical force to remove necrotic tissue. Examples include hydrotherapy, wound-scrubbing and wet-to-dry dressings. Caution should be exercised with this technique because of the potential to debride healthy granulation tissue. Wet-to-dry dressings are moistened dressings, which are applied to the wound and attach to the wound tissues on drying. On removal of the dried gauze, the attached tissue (both necrotic and healthy) is debrided. As this method is non-selective and frequently causes pain, it is generally seen as an unfavourable method of debridement. Enzymatic debridement involves application of synthetic enzymes (e.g. collagenase) to the wound bed to degrade bonds that link non-viable tissue to the wound (e.g. collagen).
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