Pressure and shear: their effects on support surface choice.

Many support surfaces are available, each with advantages and disadvantages, that claim to relieve or reduce the external forces contributing to the development of pressure ulcers. This article describes pressure and shear, and what a patient support surface must do to relieve those forces. Pressure is the vertical force of the weight of the patient's body on the surface. Shear is a horizontal force that causes the bony prominence to move across the tissue as the skin is held in place, and results from patient movement, nurse movement of the patient, and bed movement. There are seven basic requirements a support surface must meet in order to prevent pressure and shear: The surface must (1) conform to bony prominences without resistance, (2) not have significant memory, (3) allow patient immersion, (4) not bottom out, (5) relieve shear caused by patient movement, (6) prevent skin maceration, and (7) provide patient comfort. Six types of support surfaces are listed along with a summary of each surface's theoretical ability to deal with the forces described in this article. Understanding the physical forces that contribute to pressure ulcers, and each support surface's theoretical ability to relieve these forces, should make it easier to choose an appropriate support surface for each patient.