Extrinsic Risk Factors

Extrinsic factors include direct pressure, shearing forces, friction, and moisture. Direct pressure results in hypoperfusion of the affected tissue, which can lead to hypoxia, acidosis, and if prolonged, tissue death and necrosis. Pressure sores most frequently occur over bony prominences below the

Table 4-8 Risk Factors for Pressure Sore Development Table 4-9 Risk Factor Modification

Extrinsic Factors

Pressure Shear Friction Moisture

Intrinsic Factors

Impaired mobility Malnutrition Sensory impairment



Support devices to reduce pressure

Donut-type devices

Frequent repositioning

Massage over bony prominences

Positioning devices such as pillows

Raising head of bed above 30 degrees

Lifting devices such as a trapeze

Dragging the patient during transfers

waist: the sacrum, greater trochanter, malleolus, heel, ischial tuberosity, and fibular head. Of note, heels are the second most common site for pressure ulcer development. As the prevalence of pressure ulcers at other sites has decreased or remained the same, prevalence of heel pressure ulcers has increased.

Shear forces result from traction on the skin, which causes a relative displacement of the underlying structures. This usually occurs when patients are positioned in bed more than 30 degrees, or seated, and then slide down. In these patients the underlying sacrum is at risk for pressure sore development. Friction between the skin and a stationary source such as bedclothes or sheets is another factor. Care must be taken to avoid friction, especially during transfers in and out of bed. Excessive moisture can lead to skin maceration and subsequent skin breakdown. Common causes include incontinence, diarrhea, and excessive perspiration (AHCPR, 1994; Patterson and Bennett, 1995).

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