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What are the risk factors?

When looking at the risk factors for pressure ulcers, both intrinsic and extrinsic factors must be considered.

General health, nutritional status, skin moisture, age and history of previous pressure ulcers are some of the key intrinsic components that affect the risk for a patient developing pressure ulcers. Extrinsic factors include pressure, friction, shear, and microclimate.

Intrinsic risk factors

To identify intrinsic risk factors, an assessment should include:

  • General health status – Does the patient present multiple health issues? Conditions such as diabetes mellitus and respiratory conditions may increase a patient's risk for the development of pressure ulcers.
  • Mobility status – Reduced mobility affects the ability to relieve pressure on vulnerable tissues.
  • Nutritional status – Poor nutrition may have multiple effects. Nutritional status can be assessed though simple weight monitoring and the assessment of specific indicators such as hemoglobin or serum albumin.
  • Skin moisture – The effects of incontinence and body temperature should be considered when assessing skin's condition.
  • Age – The effects of age may increase risk. However, if a mix of risk factors are present, pressure ulcers can occur at any age.
  • History of previous pressure ulcers – Healed ulcer sites represent a high risk as scar tissue may only be 80% as strong as original tissue.
  • Drug history – Steroids are an example of a drug that may affect skin integrity.
  • Perfusion / oxygenation related issues – CVS instability, inotrope support, and oxygen requirements are all reported to increase the risk of pressure ulcers.

Extrinsic risk factors

Four extrinsic factors are most commonly reported to pose a risk of tissue damage:  

  • Pressure
  • Shear
  • Friction
  • Skin microclimate

It is often the combination of forces that create the highest risk for a vulnerable patient. Tissue deformation happens in soft tissue, adipose tissue, connective tissue and muscle when these forces occur. This stress and strain affect the perfusion and cellular mechanisms essential for normal functioning. In the clinical setting, non-uniform forces are usually witnessed and shear forces are often present. Age, lifestyle, and chronic illnesses can affect the ability to respond to these forces.


Definition - a force applied perpendicular to tissue

Fast Facts

  • Affected by stiffness of surface, load, tissue composition, and geometry
  • Usually expressed in lb/in2 (psi) or mmHg
  • Bony prominences can be exposed to higher stresses/strains and therefore may be reflected in deep tissue injury
  • Combination of pressure with other forces may exacerbate issues
  • Pressure wounds tend to be uniform or circular in shape and tend to present with a neat appearance
  • Influence of time – high loads experienced for short periods of time can be as damaging as smaller loads experienced for long periods of time


Definition - an action or stress resulting from applied forces which causes or tends to cause two contiguous internal parts of the body to deform in the transverse plane

Fast Facts

  • Occurs when the patient is lying flat and increases with lateral movement
  • Tissue deformation may increase when constant pressure and shear forces are present
  • Increased shear forces can exacerbate tissue damage
  • Shear-inflicted ulcers often present with a shallow area that progresses to a depth represented by bruising; skin edges may also be ragged
  • Shear forces tend to cause deeper tissue damage which may not be immediately visible
  • Changes in position are likely to cause shear – for example when the head of bed is raised or lowered


Definition – the contact force parallel to the skin surface in case of sliding – i.e. sliding of the surfaces along each other

Fast Facts

  • Friction results in the disturbance of the skin, potentially impairing its barrier ability and posing an increased risk of infection or exposing the underlying structures
  • Friction often presents as a shallow, denuded and painful area
  • The buttocks, sacrum, back elbow and heels are the most common areas for friction wounds
  • Friction wounds may be characterized by being very untidy wounds with ragged edges


Definition – the local tissue temperature and moisture at the body/support surface interface

Fast Facts

  • Moisture is known to impact the ability of the skin to function
  • Increased temperature and moisture may:

     - Reduce stiffness, soften skin, may cause maceration
     - Reduce strength of skin by up to 96% and may lead to erosion
     - Increase the co-efficient of friction
     - Increase adhesion to contact surface and may increase the risk of shear
     - Promote abrasion, slough and ulceration
     - Shift skin pH from acidic to alkaline
     - Increase metabolic rate


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