Pressures greater than approximately 32 mm Hg exceed capillary filling pressure and result in potential tissue ischemia. The standard recommendations of a 2 hour turning cycle for the immobile patient are based on animal models. Ninety percent of pressure sores occur below the waist, with two-thirds of those localized around the buttocks or hips. Location of pressure sore correlates well with pressure maps based on the anatomy of bony prominences and positioning. The initiating circumstances can often be identified by considering where the ulcer was found.
Prevalence correlates with advanced age and dependent mobility status.
Pressure is distributed non-homogenously. Normally, individuals shift weight frequently because of skin discomfort from remaining in a fixed position and unacceptable pressures for prolonged periods are avoided. When an individual is unable to recognize or respond to high pressures, skin and underlying soft tissue is placed at risk for ulceration. The key to prevention is elimination of intolerable pressure. Identification of individuals on the basis of activity level, mobility status, mental status, and incontinence often is valuable in calling attention to and focusing resources on those at highest risk.