What are pressure ulcers?
Pressure ulcers – also called pressure injuries, bedsores or decubitus ulcers – are sores that develop on the body in areas where blood supply to the tissues has been reduced due to prolonged pressure.
They can happen to anyone, but usually affect people confined to bed or who sit in a chair or wheelchair for long periods of time. If you are at risk you should be regularly monitored and offered advice and treatment to reduce the risk of pressure ulcers, but sometimes they can develop even with the highest standards of care.
While pressure ulcers can appear anywhere on the body, they are most commonly seen over bony areas such as the heels, ankles, hips and pelvis.
Why do pressure ulcers form?
Pressure ulcers form when blood flow to the tissues of the skin and surrounding area is reduced.
Amazingly, skin blood flow accounts for 5% to 10% of the blood in your body, which shows the high oxygen demand of this area.
Capillaries are the smallest blood vessels. They bring oxygenated blood from the arteries into the skin and underlying tissue, as well as taking deoxygenated blood away from the skin and tissues back into the veins.
When a person is sitting or lying on a surface the pressure between the seat/mattress and the body compresses the capillaries in this area. This is especially noticeable over bony areas, like your heels or pelvis. Just like squeezing a hosepipe if this pressure is high enough it can reduce blood flow through these capillaries or even stop it altogether.
While pressure is the most direct cause of pressure ulcers, it can also be caused by shear and friction forces.
For more information on these forces, see our article Shear and Friction in Pressure Ulcer Development.
How do we naturally prevent pressure ulcers?
If someone’s blood vessels are closed or compressed due to pressure, oxygen supply to the surrounding tissues falls. This means the cells in this area become distressed.
Interestingly, in people at full health, this fall in oxygen prompts an unconscious reflex to move; this is the reason you cross and uncross your legs or roll over in bed at night without really thinking about it! Ignore this reflex and you will start to feel pain and discomfort, a sign from your body that it’s time to get moving.
If the pressure is relieved in time, and the circulation is restored, local capillaries open up again and increased blood flow takes place. It is this that causes the pink patch on your skin you can see if you have had your legs crossed for a sustained period. This pink patch is called a ‘blanching erythema’. A blanching erythema is identifiable by the pale spot you can see when you press on it with a finger.
To see strategies to support pressure ulcer prevention click here.
What happens if we keep pressure on the skin?
If we keep pressure on the capillaries, then the reduced oxygen levels start to damage the surrounding cells. This can happen both on the surface and in deep tissues.
The first sign in the skin is often a non-blanching erythema, where the skin remains red when pressed with a finger.
Interestingly, the deep tissue area is sometimes more susceptible to damage than the skin. This means in some cases the severity of pressure injury can be tricky to grade as the skin can be less affected than the underlying muscle and fat. These are known as deep tissue injuries. As the cells are damaged, and ultimately begin to die, pressure ulcers form.
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