Measuring tissue perfusion during pressure relief maneuvers: insights into preventing pressure ulcers

BACKGROUND/OBJECTIVE: To study the effect on tissue perfusion of relieving interface pressure using standard wheelchair pushups compared with a mechanical automated dynamic pressure relief system. DESIGN: Repeated measures in 2 protocols on 3 groups of subjects. PARTICIPANTS: Twenty individuals with motor-complete paraplegia below T4, 20 with motor-complete tetraplegia, and 20 able-bodied subjects. METHODS: Two 1-hour sitting protocols: dynamic protocol, sitting configuration alternated every 10 minutes between a normal sitting configuration and an off-loading configuration; wheelchair pushup protocol, normal sitting configuration with standard wheelchair pushup once every 20 minutes. MAIN OUTCOME MEASURES: Transcutaneous partial pressures of oxygen and carbon dioxide measured from buttock overlying the ischial tuberosity and interface pressure measured at the seat back and buttocks. Perfusion deterioration and recovery times were calculated during changes in interface pressures. RESULTS: In the off-loading configuration, concentrated interface pressure during the normal sitting configuration was significantly diminished, and tissue perfusion was significantly improved. Wheelchair pushups showed complete relief of interface pressure but incomplete recovery of tissue perfusion. CONCLUSIONS: Interface pressure analysis does not provide complete information about the effectiveness of pressure relief maneuvers. Measures of tissue perfusion may help establish more effective strategies. Relief achieved by standard wheelchair pushups may not be sufficient to recover tissue perfusion compromised during sitting; alternate maneuvers may be necessary. The dynamic seating system provided effective pressure relief with sustained reduction in interface pressure adequate for complete recovery of tissue perfusion. Differences in perfusion recovery times between subjects with spinal cord injury (SCI) and controls raise questions about the importance of changes in vascular responses to pressure after SCI.