If too much pressure is exerted on the underlying tissue, this can lead to the appearance of pressure ulcers. Decisive factors for the occurrence of pressure ulcers are also specific risk factors of the patient, as well as the duration of high pressure on the tissue.
If the pressure exceeds a certain value, blood vessels may be compressed and die as a result of oxygen and nutrient deficiency.
Lying and sitting:
The risk of developing pressure sores is particularly high if there is very limited mobility, i.e. patients can only sit or lie down for a long period of time. This risk group includes above all elderly people who are confined to bed due to acute or chronic illnesses, or people who are dependent on a wheelchair. It can also frequently affect diabetics, who are less sensitive to external pressure and do not perceive it to the appropriate extent.
Pressure sores are particularly common in areas where more pressure is applied to the tissues. These include, above all, areas where there is little fat and muscle tissue, and thus the bones are not protected. Sites where bones are located directly under the skin include the buttocks, the large trochanters on the outer side of the thigh, and the heels, with the heels and buttocks being the most common sites of origin. However, unusual sites of origin may also be considered, depending on the patient's position or sitting posture. These include the ears, the back of the head, the shoulder blades, and the toes.
In rare cases, pressure ulcers can occur when the patient is in the prone position, during surgery for example. In this case, the knees, face, pubic area, and tops of the feet are the primary areas at risk for developing a pressure ulcer.
If a patient is confined to a wheelchair, for example after paraplegia, pressure ulcers are more likely to develop in the heel, buttock, toe or knee areas.
Blood supply and drainage are impaired:
Another problem is the interrupted blood supply and the reduced outflow via venous blood vessels due to the increased pressure. This condition causes an increase in acid metabolites in the tissue, which triggers a natural reflex in healthy people: movement relieves the affected part of the body, as a result of which the pressure decreases and normal blood flow to the tissue is restored.
However, if a person moves insufficiently, as is the case with bedridden patients, an accumulation of acidic metabolic products and an associated dilatation of the small arterial blood vessels occurs. The result is reddening of the skin, which is supplied with more blood due to the widening of the vessels. As a further phenomenon, fluid leaks from the blood vessels into the surrounding tissue. This results in a swelling of the tissue, in which water accumulates between the cells. Furthermore, it can be observed that blisters form and the tissue is thus more extensively destroyed.
Thin, inelastic skin:
Since pressure ulcers mostly affect older people whose skin loses elasticity and tightness over time, "sliding around in bed" can cause abrasion of the usually thin skin. This can result in the separation of entire layers of skin.
Further decisive factors for the development of a decubitus are the nutritional condition and the age of the patient, as well as the cause of the bed confinement. If the skin is already damaged by previous illnesses, as is often the case with diabetics, for example, a pressure sore can develop in less than 2 hours. If patients have less protective fat, the bone is also exposed to higher pressure.
Another cause of development is reduced control over urine or stool and the associated constant dampness in the area of the anus or vagina. Because moist skin softens more quickly, a pressure ulcer is more easily formed. Painkillers and other medications can also increase the risk of a pressure ulcer.