Subsequent assessment

The primary goal of burn care is early effective wound closure. However, the burn wound is not a static entity. In the first few days following injury the wound may appear to become deeper. Later in the course areas heal and new wounds are created (i.e. donor sites for skin grafts). Initially, the burn consists of a central area of coagulation necrosis with a surrounding zone of stasis and poor perfusion due to microvascular injury. This zone of stasis frequently progresses to tissue necrosis as the cells die of ischemia, so that a burn may 'convert' from second to third degree over the first 48 to 72 h post-injury. After this initial period, further progression of the wound usually indicates infection which must be controlled aggressively. Frequent reassessment is essential since the remaining open wound is the primary determinant of patient management and prognosis.

Today, with improved wound care and earlier surgical excision, sepsis originating in the burn wound has been replaced by pulmonary sepsis associated with smoke inhalation as the leading cause of death. However, burn wound sepsis is still a major source of morbidity, including prolonged hospitalization and skin graft loss with the need for regrafting. Infection arising in the burn wound during the first 72 h postinjury usually appears as cellulitis surrounding the margins of the burn. The offending organisms are routinely either streptococci or staphylococci. Such infections may initially be difficult to distinguish from adjacent areas of first-degree burn with erythema, heat, and pain. However, serial examinations, often over only a few hours, will demonstrate progression. Such infections occur in about 30 per cent of admitted burn patients. The use of prophylactic antibiotics for 48 to 72 h remains a disputed issue. The cellulitis usually responds promptly once it is recognized and therapy is instituted.

Of much graver concern is the issue of invasive wound infection. It is unusual for such infections to occur prior to the end of the second postburn week. The organisms involved are predominantly Gram-negative enterics and staphylococci arising from the patient's own gastrointestinal tract in at least 80 per cent of cases. The precise organisms involved tend to be unit and institution specific, having previously colonized the patient's aerodigestive tract. Bacterial colonization of the burn wound is impossible to prevent, but tissue damage can usually be minimized if the number of organisms can be kept low. When the number of organisms reaches or exceeds 100 000 per gram of tissue, local defense mechanisms are often overwhelmed and invasion into underlying healthy tissue results. The eschar, if still present, will rapidly separate, demonstrating hemorrhagic discoloration of the underlying fat and violaceous edematous wound margins. If unchecked at this level, systemic sepsis may result. The mechanism by which the wound should be monitored to detect this progression in its earliest stages remains controversial. Visual inspection may demonstrate nothing as the bacterial burden is increasing. The quantity and character of wound drainage are often obscured by the topical antimicrobial applied. The earliest indication of local infection is often a failure to show the expected progress in wound healing. The superficial partial-thickness wound should demonstrate islands of epithelium growing to confluence at a rate sufficient to produce closure in 14 to 21 days, while wounds grafted with meshed skin grafts should show adherent dry grafts at 5 days and by 7 to 10 days most of the interstices of the mesh should be filled with epithelium. Unfortunately, failure of this progression has more than one possible cause. Inadequate nutrition, poor blood supply in the wound bed, and failure to immobilize grafts adequately can all produce similar findings. For these reasons, many burn units routinely monitor the burn wound with surveillance cultures. Such surveillance techniques range from simple swab cultures to quantitative cultures to histology performed on tissue biopsies. The pros and cons of these techniques have been extensively reviewed elsewhere ( Robsgn...1991). Early recognition that control of the wound has been lost offers the best chance of minimizing the resulting damage. Regardless of the technique chosen, changes must be made in the wound management protocol when the number or depth of invasion of organisms increases.

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