A pressure injury is damage to the skin and the tissue below from pressure that lasts too long. It usually forms over a bone, where tissue is squeezed between the bone and the bed or chair.
Pressure and blood flow
When outside pressure is higher than the pressure inside small vessels, blood stops reaching the tissue. Without oxygen, cells start to die within hours, with muscle and fat often damaged before the skin.
Shear, friction and moisture
Shear happens when the skin stays still while the body slides, as when the head of the bed is raised, and it tears small vessels. Moisture from sweat or incontinence softens the skin and makes it break down faster.
Who is at risk
Patients who cannot move or feel well, such as after a stroke or spinal injury or under sedation, are at highest risk. Poor nutrition, low blood pressure and old age add to it.
Common sites
The sacrum, heels, hips, elbows and the back of the head. Medical devices such as masks, tubes and splints can also cause injuries where they press on the skin.
| Stage | What you see | Depth |
|---|---|---|
| Stage 1 | Intact skin, red that does not blanch when pressed | Skin intact |
| Stage 2 | Shallow open area or blister, pink wound bed | Partial thickness |
| Stage 3 | Full-thickness loss, fat may show | Into the fat layer |
| Stage 4 | Bone, tendon or muscle visible | Full thickness and deeper |
At the bedside
Check skin over bony areas every shift and press red spots to see if they blanch. Reposition at-risk patients regularly, often about every 2 hours, and use a risk score such as the Braden scale.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).