Cath Lab Digest

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Index: Ostomy Wound Manage. 2007;53(10):34-38.

  Pressure ulcers are a common problem that significantly contributes to morbidity and mortality among patients with spinal cord injury and other chronic conditions.¹ Pressure ulcer occurrence is frequently viewed as a medical error; efforts to improve pressure ulcer preventive care are a national priority.² However, for such efforts to succeed, a comprehensive understanding of the pathogenesis of pressure ulcers is necessary. As emphasized in one editorial on pressure ulcers, “a strategy designed to limit or solve a problem requires, first and foremost, a clear understanding of the nature and underlying causes of the problem.”³

  Although understanding of pressure ulcer pathogenesis has advanced considerably, confusion still exists among many clinicians. Organizations such as the National Pressure Ulcer Advisory Panel (NPUAP) are examining new data as they grapple with issues such as what defines a superficial pressure ulcer, what constitutes deep tissue injury, and whether the currently used staging system adequately reflects current knowledge.⁴ Traditionally, pressure, shear, friction, and moisture were the major external factors considered to have a causative role in pressure ulcer development.⁵ However, these factors need to be re-examined and factors such as heat, stress, strain, and reperfusion injury considered. Data on pressure ulcer pathogenesis are reviewed herein with regard to an important question in the management of patients with spinal cord injury: Are all pressure ulcers the result of deep tissue injury?

  In order to comprehensively address this question, three corollary questions need to be discussed: 1) what is the nature of pressure-induced tissue injury? 2) are clinically superficial skin injuries induced by pressure associated with deep tissue damage? and 3) if not pressure, what causes most superficial ulcers? A review of the relevant literature was conducted to determine whether all pressure ulcers result from deep tissue injury.

Pressure and Tissue Injury

  How does pressure damage tissue and which tissues are most susceptible to pressure-induced damage? To address this, it is necessary to discuss the fundamental pathophysiological cause(s) of pressure ulcers. The four most commonly hypothesized pathophysiological explanations for the development of pressure ulcers include 1) ischemia caused by capillary occlusion⁶; 2) reperfusion injury – ie, injury resulting from the accumulation of substances associated with the inflammatory response to ischemia as blood is reintroduced into an ischemic region^7,8; 3) impaired lymphatic function that causes metabolic waste products, proteins, and enzymes to accumulate^9,10; and 4) prolonged mechanical deformation of tissue cells.¹¹ Most likely, all four are contributing factors. Regardless of their relative importance, each of the aforementioned factors is fundamentally caused by stress (pressure) and strain (deformation) in soft tissue. The question regarding how force exerted on the skin affects the underlying tissues and subsequently increases risk of pressure ulcer development can be logically simplified to a contemplation of the external forces that cause stress and strain in underlying soft tissue. It is useful to consider that the forces acting on the skin are reactive, countering the gravitational forces that pull the body toward Earth. These gravitational forces are concentrated at various posture-dependent, weight-bearing bony prominences such as the heel, sacrum, and pelvis.