Deep tissue injury from a bioengineering point of view

The phrasing of the National Pressure Ulcer Advisory Panel's (NPUAP) definition of deep tissue injury (DTI) was based on case reports, clinical observations, and experience. Although etiological studies of DTI, primarily related to characterizing biomechanical factors affecting onset and progression, support and strengthen parts of the NPUAP's definition, some recent findings suggest a need to re-evaluate the wording and perhaps refine future definitions of DTI. Application of existing bioengineering research to underlying biological, physical, biomechanical, and biochemical mechanisms involved in the definition of DTI suggests the following: 1) changes in skin color - ie, deviation of the local skin color from the surroundings - may indicate a DTI might be present, but color is not useful for quantifying the severity of injury; 2) the pressure and/or shear definition is inaccurate because it creates an artificial distinction between pressure and shear, which are physically coupled, and because it ignores tensional loads; 3) palpating tissue firmness at the wound site provides limited assessment information because tissue firmness will depend on the point in time along the course of DTI development. Damaged tissues might appear stiffer than surrounding tissues if examined when muscle tissue is locally contracted due to local rigor mortis but at a later stage damage might manifest as tissues that are softer than their surroundings when digestive enzymes start decomposing necrotic tissues; 4) skin temperature changes near the DTI site may reflect inflammatory response, causing local heating, or ischemic perfusion, causing local cooling; and 5) rapid deterioration of DTI is likely occurring due to muscle tissue stiffening at the rigor mortis phase; stiffened tissues abnormally deform adjacent tissues and this effect is amplified if muscles are atrophied. The application of interdisciplinary research may help clinicians and researchers move from evolving jargons, staging systems, and injury definitions to valid and reliable clinical instruments, which will improve clinical practice.