4. Pressure ulcers comprise the fourth major type of wounds. These typically occur in people who are bedridden or whose mobility is severely limited. They are caused by a loss of blood circulation that occurs when pressure on the tissue is greater than the perfusion pressure in capillaries, thereby cutting off circulation, rendering tissue ischemic. The combination of anesthesia and paralysis is a potent inducer of tissue break down. Data from spinal cord units at Veterans Affairs Medical Centers show an alarmingly high prevalence and incidence of pressure ulcers in young soldiers paralyzed by spinal cord injuries.