Pressure ulcers are mainly caused by localized pressure on the body for a long period of time, causing obstruction of blood circulation, resulting in ischemia of the local skin and subcutaneous tissues here, which leads to a series of manifestations such as erythema, blistering, ulceration and even necrosis, and is often clinically divided into four phases.1. Phase I pressure ulcer bruising and erythema: The clinical definition of Phase I is a red, swollen, hot, painful or numb feeling at the pressure ulcer that does not subside for 30 minutes. . In addition, in the more raised areas of the skin, there will be limited erythema, and pressure will not fade; 2. Phase II pressure sore inflammatory infiltrative phase: clinically visible symptoms such as purple-red, hard nodules, pain, and blisters, with shallow open ulcers on the surface of the pressure sore, accompanied by pink trauma, which may also manifest as an intact or ruptured serous blister; 3. Phase III pressure sore superficial ulcerative phase: clinically defined in Phase III, there will be significant of epidermal rupture and ulcer formation. The subcutaneous fat is even visible at the pressure ulcer, but the bones, tendons, and muscles are not exposed, and there will also be rotting flesh present, which smells foul. 4. Stage IV pressure ulcer necrotic ulcer stage: clinically, the breakage of the pressure ulcer is seen to have invaded the subdermis, muscle layer, bone surface, and can even be seen in the bone, tendons, or muscles, and there is rotting flesh or scorched crust in some parts of the wound bed, often with submersion or tunneling.