Clinical meaning
Burns are tissue injuries caused by thermal, chemical, electrical, or radiation energy that produce cellular damage ranging from reversible injury to complete tissue destruction. Thermal burns are the most common type, caused by contact with flames, hot liquids (scalds), hot surfaces, or steam. Understanding burn pathophysiology requires knowledge of Jackson's burn wound model, which describes three concentric zones of tissue injury. The zone of coagulation is the central area of the burn wound where temperatures were highest, causing irreversible protein denaturation and coagulative necrosis of all cells. This tissue is non-viable and cannot recover regardless of treatment. The zone of stasis surrounds the zone of coagulation and represents tissue with decreased perfusion and potentially salvageable cells. Cells in this zone have sustained thermal injury but are not yet irreversibly damaged -- they exist in a precarious state where adequate resuscitation and wound care can preserve viability, but inadequate resuscitation, infection, edema, or vasoconstriction can convert this zone to coagulative necrosis (wound deepening). Preventing zone of stasis conversion is a primary goal of burn management. The zone of hyperemia is the outermost zone where tissue has sustained minimal injury but demonstrates increased blood flow (hyperemia) as part of the inflammatory response. This tissue will recover completely unless complicated by severe sepsis or prolonged hypoperfusion. Burns are classified by depth: superficial (first-degree) burns involve only the epidermis (sunburn is the prototype -- erythema, pain, no blistering, heals in 3-7 days without scarring). Superficial partial-thickness (superficial second-degree) burns extend through the epidermis into the superficial (papillary) dermis -- they produce blisters with a moist, pink, painful wound bed that blanches with pressure (indicating intact dermal blood supply); these wounds heal in 7-21 days from surviving epithelial appendages (hair follicles and sweat glands) with minimal scarring. Deep partial-thickness (deep second-degree) burns extend into the deep (reticular) dermis -- the wound appears mottled pink and white, with decreased sensation (damaged nerve endings), sluggish capillary refill, and may or may not blister; healing takes 3-8 weeks with significant risk of hypertrophic scarring. Full-thickness (third-degree) burns destroy the entire epidermis and dermis -- the wound appears white, waxy, brown, or charred, is insensate (destroyed nerve endings), does not blanch with pressure, feels leathery (eschar), and CANNOT heal without skin grafting because all epithelial regenerative structures have been destroyed. Fourth-degree burns extend through the full thickness of skin into underlying subcutaneous tissue, fascia, muscle, or bone. Burn size is assessed using standardized methods. The Rule of Nines divides the adult body surface into regions each representing 9% (or multiples): head 9%, each upper extremity 9%, anterior trunk 18%, posterior trunk 18%, each lower extremity 18%, perineum 1%. For children, the Lund-Browder chart provides more accurate age-adjusted calculations because children have proportionately larger heads and smaller extremities. For scattered or irregular burns, the patient's palm (including fingers) represents approximately 1% of total body surface area (TBSA). Only partial-thickness and full-thickness burns are included in TBSA calculation -- superficial (first-degree) burns are excluded. The systemic response to major burns (>20% TBSA in adults, >10% in children) is a massive, life-threatening physiological derangement. Within minutes of injury, massive release of inflammatory mediators (histamine, prostaglandins, kinins, cytokines including IL-1, IL-6, IL-8, TNF-alpha) from damaged tissues causes a dramatic increase in capillary permeability throughout the body (not just at the burn site). This systemic capillary leak results in massive shifts of intravascular fluid, electrolytes, and plasma proteins into the interstitial space (third-spacing), producing burn shock -- a combination of hypovolemic (from fluid loss) and distributive (from vasodilation and capillary leak) shock. Without aggressive fluid resuscitation, burn shock progresses to cardiovascular collapse and death within hours. Fluid resuscitation is guided by the Parkland (Baxter) formula: 4 mL x body weight (kg) x %TBSA burned of lactated Ringer's solution in the first 24 hours, with half given in the first 8 hours from the TIME OF INJURY (not time of arrival to hospital) and the second half over the next 16 hours. The target of resuscitation is a urine output of 0.5-1 mL/kg/hour in adults (1-2 mL/kg/hour in children), which serves as the primary indicator of adequate end-organ perfusion. Fluid resuscitation is titrated to urine output, not given as a fixed rate -- the Parkland formula provides a starting estimate, but actual requirements may be higher or lower. The capillary leak phase typically resolves by 18-24 hours post-burn, after which capillary integrity is restored and mobilization of third-spaced fluid begins (heralded by a spontaneous diuresis). The RN's role in burn assessment is critical: accurate initial burn size and depth estimation directly determines resuscitation requirements, transfer criteria, and surgical planning. Common errors include overestimating burn size (including erythema/first-degree burns in TBSA), underestimating depth (deep partial-thickness burns may initially appear superficial before wound evolution), and starting the 24-hour clock from hospital arrival rather than from time of injury. The nurse must also perform a systematic primary and secondary trauma survey because burns may coexist with other traumatic injuries (inhalation injury, fractures from falls or explosions, blast injuries).