Bony Prominence: An area where bone lies close to the skin’s surface, such as the sacrum, heels, ischial tuberosities, and trochanters. Bony prominences are common sites for pressure injury development.

Deep Tissue Pressure Injury (DTPI): A subtype of pressure injury presenting as discolored intact skin or a blood-filled blister due to damage of underlying soft tissue from pressure and/or shear. It often originates in muscle layers and may rapidly progress to full-thickness necrosis.

Friction: A mechanical force generated when 2 surfaces move across each other, causing superficial skin damage such as abrasions. Friction alone may not cause deep tissue injury but weakens the epidermis and amplifies the effects of shear and pressure.

Ischemia: A restriction of blood flow to tissues, depriving them of oxygen and nutrients. In pressure injuries, ischemia results from capillary occlusion when external pressure exceeds the normal capillary closing pressure.

Maceration: The softening and breakdown of the skin due to prolonged moisture exposure (eg, incontinence, perspiration, wound exudate). Macerated skin is more vulnerable to friction and shear injury.

Medical Device-Related Pressure Injury (MDRPI): A pressure injury caused by a diagnostic or therapeutic device, where the injury pattern mirrors the device’s shape or contact points. Common sites include the face, ears, nares, and mucous membranes.

Microclimate: The local temperature and moisture conditions at the skin-surface interface. Poor microclimate management (eg, heat and humidity under devices or dressings) reduces skin tolerance and increases PI risk.

Pressure Injury (PI): Localized damage to the skin and/or underlying soft tissue, usually over a bony prominence or under a medical device, caused by sustained pressure, or pressure combined with shear and/or friction, resulting in tissue ischemia and necrosis.

Prophylactic Dressing: In the context of pressure injuries, a protective dressing applied to at-risk skin to reduce friction, shear, and moisture accumulation.

Repositioning: The systematic changing of a patient’s position to periodically redistribute pressure on at-risk areas.

Shear: A tangential mechanical force that occurs when layers of tissue slide over one another, stretching and distorting blood vessels. Shear disrupts microcirculation and is a key contributor to deep tissue injury.

Support Surface: A specialized mattress, overlay, or cushion designed to redistribute pressure and minimize shear. Static surfaces (foam, gel, air-filled) distribute pressure evenly; dynamic surfaces (alternating air, low-air-loss) actively change load points to relieve pressure.

Tissue Deformation: The distortion of cells and extracellular structures due to sustained pressure or shear. This mechanical strain disrupts cellular membranes, triggers inflammatory signaling, and can lead to cell death within minutes, even before ischemia develops.

Tissue Tolerance: The ability of skin and underlying structures to endure pressure without damage. Tissue tolerance may be influenced by both intrinsic factors (age, nutrition, vascular health, diabetes) and extrinsic factors (moisture, temperature, shear).