Energy cost of fat-fuel mobilization in geriatric trauma.

Age-related changes in body composition may result in varied responses to acute accidental injury. Gaining fat as age advances is common and therefore the mobilization of fat fuel resources in traumatized geriatric patients needs closer examination. We have measured in six elderly (age, 60 to 74 years) and seven young (age, 18 to 46) traumatized, hypermetabolic, and highly catabolic patients, in the "flow phase" of the metabolic response to injury, the rates of whole-body lipolysis and net fat oxidation. This enabled us to calculate the rate of triglyceride/free fatty acid (TG/FFA) cycling in the whole body and to assess its contribution to energy expenditure. Energy metabolism in general and the fat metabolism in particular were found to be somewhat slowed in elderly trauma patients compared with equally injured young individuals, although the aged patients had more total body fat. The energy cost of TG/FFA cycling is significantly (P less than .025) lower in elderly trauma victims (0.28 +/- 0.06 kcal/kg/d) compared with young patients (0.63 +/- 0.1 kcal/kg/d). This can account for approximately 3% to 4% of the elevation in metabolic rate over that predicted in the uninjured state.