The Relative Significance of Thermal and Metabolic Demands on Burn Hypermetabolism

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Abstract

To evaluate the claim that burn hypermetabolism can be eliminated by making patients warm and comfortable, respiratory gas exchange was measured, using a canopy hood system, in 20 burn patients and five normal controls resting in a 30°C ambient environment. Metabolic rates of burn patients determined by the canopy hood system were comparable to previous values obtained using Douglas bag techniques. In another study, the effects of induced hyperthermia were evaluated in seven febrile, hypermetabolic burn patients. External heating elevated rectal temperatures from 38.6 ± 0.3 to 39.4 ± 0.2 (mean ± S.E.M., p < 0.001) but did not significantly reduce metabolic rate (76.5 ± 3.7 kcal/m2± hr vs. 73.9 ± 3.5). When five normals and seven burn patients adjusted room temperature until they were comfortable, the “preferred‘’ environmental temperature selected by the burn patients was 31.5 ± 0.7°C, significantly warmer than the 28.6 ± 0.7°C selected by the controls. In this comfortable environment the sleeping, febrile burn patients remained hypermetabolic (63.9 ± 5.7) and the Q10 effect of the hyperpyrexia accounted for only 20 to 30% of the hypermetabolism observed.

These studies demonstrate that the hypermetabolic response to burn injury is not significantly reduced in comfortable patients resting or sleeping in a warm environment, and the increased oxygen consumption cannot be accounted for by the elevated body temperature. This evidence does not support the contention that burn hypermetabolism is primarily the result of thermoregulatory drives. The increased heat production following injury is the consequence of an elevated metabolic state.

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