Clinical meaning
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 wound base obscured by slough (yellow) or eschar (black); cannot be staged until debridement reveals the wound bed. Deep tissue pressure injury (DTPI) — intact or non-intact skin with localized area of persistent non-blanchable deep red, maroon, or purple discoloration; represents damage to underlying soft tissue from pressure/shear; may evolve rapidly. The Braden Scale (scored 6-23) assesses six domains: sensory perception, moisture, activity, mobility, nutrition, and friction/shear. Score <=18 indicates at-risk; <=12 indicates high risk.