The National Pressure Advisory Board developed a classification system for staging ulcers. There are four stages:Stage One: A redden area of the skin that does not turn white when you press it.Stage Two: Partial thickness skin loss involving the top to layers of the skin: the dermis and epidermis. This looks like a blister or abrasion.
Full thickness skin loss involving the subcutaneous tissue and maybe theunderlying facia. This presents as a deep crater and might involve adjacent tissue.Stage Four: Full thickness skin loss with extensive destruction, tissue death, muscle, tendon damage, or damage to bone.A constant pressure of 70 mm of mercury for more than two hours leads to tissue death.
If pressure is intermittently relieved, minimal changes occur. Thus, the standard of turning patients is every two hours. This traditional recommendation is a minimal requirement and actually is dependant on the degree of patient mobility and the support surface used.