Not just skin deep
Pressure ulcers can form in the deep tissue, so looking at the surface of the skin won’t necessarily tell you whether a patient is safe and despite what the name suggests, pressure isn’t the only cause.
From our experience a number of extrinsic factors increase the risk of pressure ulcers, including pressure, shear, friction and microclimate
Friction - A force that occurs when skin slides against another surface. One example of friction is when gravity causes a patient to slip down the bed. The amount of friction depends on how easily the two surfaces can move across each other, and on how much pressure is applied
Pressure - A force applied at right angles to the surface of the skin. Pressure compresses the tissue and can deform skin and soft tissues such as subcutaneous fat and muscle. Deformation is greater when pressure is applied over a bony prominence
Shear - A result of friction, pressure and movement. Changes in position are likely to cause shear, such as when the head of the bed is raised or lowered. Shear forces tend to cause deeper tissue damage that may not be visible immediately
Microclimate - The temperature and moisture levels where skin and support surface meet. Higher skin temperatures lead to sweating. The accumulation of heat and moisture has been shown to weaken skin and increase the amount of friction and shear between the skin and support surface
'Superficial' versus 'deep' pressure ulcers: Possible difference in development
Expert opinion on the causes of pressure ulcers has evolved. We now believe that different types of pressure ulcers may develop in different ways: shallower pressure ulcers are thought to start at the surface of the skin, while those that are more severe are thought to start in the deep tissue
Outside in/top down pressure ulcers
- Caused by superficial damage
- Stage I and II pressure ulcers
Friction and shear at the surface of the skin (or in other factors such as irritant dermatitis) may cause superficial damage. This may also lead to increased shear and pressure in deeper tissues, which results in deeper damage
Inside out/ bottom up pressure ulcers
- Caused by deep-tissue damage
- Stage III and IV pressure ulcers
Pressure and shear cause deep tissue damage near a bony prominence, which then extends outwards towards the surface of the skin
'References'
