| Sign | Abnormality |
|---|---|
| General condition | Lethargy-electrolyte imbalance Analgesic effects Hyperventilation Pain, topical agents Tachycardia Pain, volume depletion, hypermetabolism |
| Fluid balance | Hypovolemia Initial injury Delayed-evaporative loss |
| Fluid composition | Hypernatremia Free water loss Inadequate fluid replacement Hyponatremia Excessive free water Effects of topical silver nitrate Hyperglycemia Stress |
| Temperature | Hypothermia Heat loss to the environment Large fluid requirement Hyperthermia Hypermetabolism Endotoxin from the wound |
| Neutrophil response | Neutrophilia Acute 5–7 days after injury Neutropenia 2–3 days after injury |
Injury pathophysiology and susceptibility to infection
The initial approach to the burn-injured patient is oriented toward limiting the progression of the injury by stabilization of the patient and maintenance of blood flow to the wound. The zone of coagulative necrosis consists of tissue that has been irreversibly damaged, whereas the surrounding zone of stasis contains areas of potentially reversible injury. Adjacent areas, known as the hyperemic zone, may also evolve to become necrotic if the blood flow is not maintained. For this reason, the primary goal of early burn therapy is to ensure adequate delivery of oxygen, nutrients, and circulating cells to the wound. In addition to prevention of progression of the injury, immediate burn care focuses on maintenance of a viable tissue interface at which both specific and nonspecific defenses against infection can be mounted.
The depth of burn injury is categorized as partial or full thickness. Full-thickness injuries will heal only by contraction, ingrowth of surrounding epidermis, or grafting of tissue because all epidermis in the wound has been destroyed. These wounds are leathery and dry, contain thrombosed vessels, and are insensate. Partial thickness wounds contain residual epidermis, which can close the wound if blood flow is maintained and infection does not supervene.
Partial thickness wounds are red and moist, and pain is elicited by touch. Deep partial-thickness wounds contain only epithelial elements associated with organelles of the skin. They take longer to heal (2 to 3 weeks) than superficial partial-thickness wounds, and there is a greater functional and cosmetic deformity if they are allowed to heal primarily. These wounds are difficult to differentiate by clinical evaluation from superficial partial-thickness injuries, which usually heal within 10 days to 2 weeks.
The dynamic aspect of burn wounds is dramatically seen when partial-thickness wounds convert to full-thickness wounds during a difficult resuscitation of a patient. Although this is rarely seen with current methods of resuscitation, resuscitation that is delayed or performed on patients at extremes of age occasionally will show this progression.
Any agent that causes cellular death can lead to a deeper wound. With this in mind, caustic topical agents and vasopressors are avoided, the wound is not allowed to desiccate, and the patient is kept warm.
Both mortality and susceptibility to infection correlate directly with the extent of the surface area injury. Distribution of surface area varies with age, so a chart is used to plot accurately the extent and depth of surface area burned. The rule of nines may be used to estimate the extent of injury as follows: torso, back and front, each 18%; each leg 18%; each arm 9%; and head 9%. Calculation of the extent of injury is helpful in estimating fluid requirements and prognosis. Patients with greater than 25% to 30% total body surface area burn exhibit the pathophysiologic features already described.
Prevention of infection
Current data do not support the general use of prophylactic systemic antibiotics in the inpatient population. Frequent evaluation of the wound and surrounding tissue allows early and appropriate therapy of cellulitis while sparing a majority of patients exposure to unnecessary antibiotics. However, some practitioners give systemic antibiotics (cephalexin) to outpatients with burns because it is not possible to observe closely and ensure appropriate care of the wound. The use of systemic antibiotics in these patients is individualized such that those who are likely to follow up with their care and recognize changes in their wounds are not given antibiotics. The one time that prophylactic systemic antibiotics are used in inpatients is at the time of surgical manipulation because this may cause bacteremia. Antibiotics are administered immediately before and during burn wound excision. The choice of antibiotics is dictated by knowledge of the current flora in the burn center or, more specifically, by the burn wound flora of the individual patient.
The mainstay of prevention of burn wound infection is aggressive removal of the necrotic tissue and closure of the wound with autograft. In the interim, topical antimicrobial prophylaxis will decrease the incidence of conversion of partial-thickness to full-thickness wound by local infection, and these agents may prolong the sterility of the full-thickness burn wound. Silver sulfadiazine is the most commonly used topical agent and is a soothing cream with good activity against gram-negative organisms. Because it does not penetrate the wound, it is used only as a prophylactic antimicrobial. Bacterial resistance to silver sulfadiazine has been reported, and it has been reported to cause neutropenia. Silver
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