Assessment of pressure ulcer category
The four categories of pressure ulcers
Pressure ulcers are the result of persistent pressure or shear of the skin and underlying tissues – typically in places on the body where the bones are close to the skin and where there is little fat.
Pressure occurs when a person’s weight is pressed down against the ground. Whether the person is lying, sitting or standing, the pressure is transmitted to the underlying tissue and the tissue is compressed between the surface and the bone. Muscle tissue does not tolerate as much pressure as skin. Therefore, the damage will occur close to the bone and often only be visible on the skin 1-2 weeks after it has been exposed to pressure.
In shear, a torsion occurs that damages tissues and blood vessels. This means that less pressure is needed to reduce blood flow to the injured area. Therefore, pressure damage to tissues exposed to shear will occur more quickly.
Pressure is caused by a lack of change in position or external pressure from medical equipment such as oxygen and catheters.
Shear occurs when the body is moved without being lifted off the ground. This can happen, for example, when a person sits with a raised headboard and slides into bed.
In addition to the above four categories of pressure ulcers, two other categories have been added which are relevant when a pressure ulcer is observed but it is not possible to categorise the ulcer as category 1, 2, 3 or 4.
The other two categories are;
- suspected deep tissue injury
- unclassifiable pressure ulcer
A pressure ulcer can be categorised as suspected deep tissue injury if an area of skin with tissue damage due to pressure or shear is seen that is expected to develop into a deep pressure ulcer but has not yet done so.
The skin around the pressure injury is typically discoloured purple or reddish brown and may show haemorrhagic (blood-filled) blisters. Haematoma (blood collection) also indicates deep tissue damage. It can be painful and oedematous (swollen).
It can be either warmer or cooler than the surrounding tissue.
The evolution to a deep wound can be rapid even with optimal treatment.
A pressure ulcer can be categorised as unclassifiable if there is complete loss of skin layer, with the actual depth of the ulcer not visible due to slough (yellow, light brown, grey, green or brown) and/or crust (light brown, brown, black) in the wound bed. It is not possible to determine whether the wound is grade 3 or 4 until enough slough and/or crust has been removed to expose the base of the wound.
Intact skin with redness, lack of capillary response
Typically over a bone spur.
The area may be painful, firm, soft, warmer or colder than the surrounding tissue.
It may be more difficult to observe redness in people with brown and black skin. Here it is essential to observe whether there are areas of skin around bone prominences that have a different colour from the rest of the surrounding tissue.
A category 1 pressure ulcer may indicate that the person is at risk of progression to a full-blown ulcer – that is, a category 2 or higher pressure ulcer.
Partial skin loss or blistering
Partial skin loss appearing as a superficial, open wound with a red/pink wound bed, without dead tissue. May also appear as an intact, or open/cracked serous (thin fluid) or bloody blister. It must be a shiny or dry, superficial wound without dead tissue or haematoma (blood collection) to be categorised as a category 2 pressure ulcer.
It is essential to be aware of. this category is often confused with skin lacerations, tape or bandage injuries, abrasions, incontinence-related dermatitis or maceration. The latter two are instead categorised as moisture-related skin damage. Read more about these and other moisture-related skin conditions here.
Full skin loss
Complete loss of skin layer. Subcutaneous fat may be visible, but bones, tendons or muscles are not exposed. Necrosis (dead tissue) can be seen, but it does not hide the depth of the pressure ulcer. There may be undermining and fistulae. The depth of category 3 pressure ulcers varies according to anatomical location.
Wound undermining occurs when there is significant erosion (loss of cells on the surface of a tissue) below the outwardly visible wound edges, resulting in more extensive damage below the skin surface. Therefore, the outer wound will typically appear small, but there will be large areas of tissue loss below the surface.
A fistula is an abnormal passage between a specific area of the body and an external or internal body surface. A fistula is usually tubular.
Deep tissue damage
Loss of any tissue layer with visible bone, tendon or muscle. Necrosis (dead tissue), fibrin (seen as a jelly-like coating) and slough (yellow or white coating of dead cells, generally wet with soft texture) may be present.
The depth of category 4 pressure ulcers varies according to anatomical location. In places on the body with little subcutaneous fat, such as the bridge of the nose, ears and malleoli, category 4 pressure ulcers can be superficial. Elsewhere on the body, category 4 pressure ulcers are typically deep and often with undermining and fistulae.
Because category 4 pressure ulcers typically extend to muscles, tendons and bones, there is a risk of infection of the bones (osteomyelitis or osteitis).
