dermatologic disorders
Pressure Injuries
Pathophysiology of Pressure Injuries
The main factors contributing to pressure injuries are Pressure:When soft tissues are compressed for prolonged periods between bony prominences and external surfaces, microvascular occlusion with tissue ischemia and hypoxia occurs. Pressures exceeding normal capillary pressure (range is 12 to 32 mm Hg) result in reduced oxygenation and compromise the microcirculation of the affected tissue. If compression is not relieved, a pressure injury can develop in 3 to 4 hours. This most commonly occurs over the sacrum, ischial tuberosities, trochanters, malleoli, and heels, but pressure injuries can develop anywhere. Friction:Friction (rubbing against clothing or bedding) can help trigger skin ulceration by causing local erosion and breaks in the epidermis and superficial dermis. Shearing forces:Shearing forces (eg, when a patient is placed on an inclined surface) stress and damage supporting tissues by causing forces of muscles and subcutaneous tissues that are drawn down by gravity to oppose the more superficial tissues that remain in contact with external surfaces. Shearing forces contribute to pressure injury but are not direct causes. Moisture:Moisture (eg, perspiration, incontinence) leads to tissue breakdown and maceration, which can initiate or worsen pressure injuries. Because muscle is more susceptible to ischemia with compression than skin, muscle ischemia and necrosis may underlie pressure injuries resulting from prolonged compression. 