Pathophysiology
Clinical meaning
Burns are classified by depth affecting skin layers and total body surface area (TBSA) involved. Superficial (first-degree) burns affect the epidermis only, presenting with erythema and pain without blisters (sunburn). Partial-thickness (second-degree) burns extend into the dermis: superficial partial-thickness involves papillary dermis with painful, moist, pink wounds with intact blisters; deep partial-thickness involves reticular dermis with decreased sensation and dry, pale appearance. Full-thickness (third-degree) burns destroy the entire dermis and may extend into subcutaneous tissue, presenting as painless, leathery, white, brown, or charred tissue. The Rule of Nines estimates TBSA in adults: each arm 9%, each leg 18%, anterior trunk 18%, posterior trunk 18%, head 9%, perineum 1%. Jackson's burn model describes three zones: zone of coagulation (irreversible necrosis), zone of stasis (potentially salvageable), and zone of hyperemia (will recover). Fluid resuscitation using the Parkland formula (4 mL × kg × %TBSA) is critical for burns > 20% TBSA to prevent burn shock.