Pressure sores: prolonged pressure and local tissue ischaemia
A pressure sore is breakdown of skin and tissue over a bony prominence (a weight-bearing bony area), caused by prolonged pressure that reduces blood flow and causes ischaemia.
Remember
Prolonged pressure over a bony prominence reduces blood flow and causes ischaemia, so pressure sores are largely preventable by regular repositioning, which relieves the pressure.
In a pressure sore, prolonged pressure squeezes the tissue between a bony prominence and the surface the patient lies or sits on. The small blood vessels are compressed, so blood flow falls and the cells are starved of oxygen. This is ischaemia. How bad the damage becomes depends on both how intense the pressure is and how long it lasts.
If the pressure is not relieved, the cells die (necrosis) and the skin and the tissue under it break down into an ulcer. The first visible sign is non-blanching erythema, which means red skin that does not fade when pressed. It reflects damage from ischaemia before the skin breaks down.
Shear forces (sliding forces, typically generated when people slide down in a bed or chair) can stretch and tear small blood vessels. Friction and moisture can make the damage worse. Without pressure there is no pressure sore.
Pressure sores usually form on the heels, elbows, hips, sacrum and tailbone, the bony areas that bear weight when a person is lying or sitting. Reduced mobility is an important risk factor, and poor nutrition and older age raise the risk too.
Pressure sores are painful, and once the skin barrier is broken there is a large risk of infection. They are linked with higher mortality, but they are largely preventable. Regular repositioning (moving the patient at intervals) relieves the pressure and is the core of prevention.
Key facts
- Cause
- sustained pressure, with or without shear (sliding forces), over a bony prominence.
- Mechanism
- the blood supply to compressed tissue falls, so its cells are starved of oxygen and die if the pressure is not relieved.
- Early sign
- non-blanching erythema, which is red skin that does not fade when pressed.
- Typical sites
- heels, elbows, hips, sacrum and tailbone.
- Extra factors
- shear, friction and moisture add to the damage but are not the main cause.
- Risk factors
- reduced mobility, poor nutrition and older age.
- Core of prevention
- regular repositioning of the patient, which relieves the pressure.
Exam traps
- Autoimmune destruction of skin does not explain a pressure sore, because the immune system does not destroy the skin in its development: the injury follows pressure.
- Infection of intact skin does not start a pressure sore: infection is a secondary complication that follows broken skin, because intact skin is a barrier.
- Friction from bed linen can tear the skin surface, but that surface damage is not the deep damage caused when pressure reduces the blood flow to the tissue.
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