Pressure Injury Staging

A pressure injury is localized damage to the skin and/or underlying soft tissue, usually over a bony prominence or beneath a medical or therapeutic device. Sustained pressure, or pressure combined with shear, distorts tissue and reduces its ability to receive oxygen and clear metabolic waste. Several mechanisms act together. Loading can compress blood vessels and cause ischaemia; reperfusion after pressure is relieved can generate additional tissue injury; direct deformation can damage cells even before prolonged ischaemia develops; and impaired lymphatic drainage allows fluid, inflammatory mediators, and waste to accumulate. There is no reliable universal pressure-time threshold. High deformation may injure cells within minutes, while the familiar “capillary closing pressure” explanation describes only one part of the process and should not be used as a bedside timer. Muscle is more susceptible than skin to pressure-related damage. Injury may therefore begin at the bone-muscle interface and appear later as a surface colour change or blister. That deeper-to-superficial pattern explains why a small skin finding can conceal extensive tissue destruction and why a deep tissue pressure injury can evolve quickly. Staging describes the...