Wound care |

Aetiology of pressure ulcers*

The development of a pressure ulcer is a complex interaction between extrinsic factors (environment) and intrinsic factors (patient related).

Tissue Deformation

 A pressure ulcer is defined as tissue damage caused by unrelieved pressure, friction, shear forces to tissue between a surface and a bony prominence. To understand the mechanism of this injury one must consider the effects of these forces at a cellular level. Pressure, friction and shear forces are interlinked and can exert sufficient deformational force on cells to cause damage to cellular components such as the cytoskeleton of the cell. This damage may result in the failure of the cell membrane to maintain its function of regulating the transport of ions from the extracellular environment.The failure of the cell membrane rapidly leads to cell death. The death of multiple tissue cells results, ultimately, to the formation of areas of tissue necrosis.

Pressure 

skin 1

Shear 

skin 2

Friction

skin 3

 

Ischemia

In parallel to this cell level damage one must also consider the effects of pressure, friction and shear forces to the vasculature of compromised tissue. These forces combine in certain instances to deform and compromise the ability of blood vessels to supply adequate oxygen levels to tissues (ischaemia) and ultimately cells which leads to the accumulation of waste products, changes in cellular pH and eventually cell death.

This process is commonly believed to develop over a period of hours as opposed to that of cellular deformation which is a more rapid process.

Microclimate

An important additional factor in the development of pressure ulcer is that of microclimate which constitutes the temperature and the degree of moisture at the skin/surface interface. Raised skin temperature combined with high moisture levels from sweat, urine or wound exudate can combine to raise the risk of pressure ulcer through increasing metabolic needs of the skin, decreasing the skin’s mechanical resistance to external forces and to increasing the frictional forces between the skin and a support surface.

An individual’s risk of developing a pressure ulcer is further influenced by intrinsic factors such as their age, ability to reposition, mental status, nutritional status, level of tissue perfusion and a range of comorbidities which may be present.

* World Union of Wound Healing Societies (WUWHS) Consensus Document. Role of dressings in pressure ulcer prevention. Wounds International, 2016