Pressure injuries (formerly pressure ulcers or decubitus ulcers) result from prolonged, unrelieved pressure on tissue, causing localized damage to skin and/or underlying soft tissue usually over a bony prominence. The primary mechanism is tissue ischemia: external pressure exceeding capillary closing pressure (~32 mmHg) occludes blood flow, causing ischemia, hypoxia, metabolic waste accumulation, and cellular death. Contributing factors include shear (parallel forces that cause tissue layers to slide against each other, damaging blood vessels), friction (superficial skin damage from rubbing), and moisture (maceration weakening the stratum corneum). Staging: Stage 1 — intact skin with non-blanchable erythema (press and release the reddened area; if it does NOT blanch/turn white, it is Stage 1). Stage 2 — partial-thickness skin loss involving epidermis and/or dermis; presents as a shallow open ulcer with red-pink wound bed, or intact/ruptured serum-filled blister. Stage 3 — full-thickness skin loss; subcutaneous fat may be visible but bone, tendon, and muscle are NOT exposed; may include undermining and tunneling. Stage 4 — full-thickness tissue loss with exposed bone, tendon, or muscle; may include osteomyelitis. Unstageable — full-thickness tissue loss with...