Protein and glucose fuel kinetics and hormonal changes in elderly trauma patients

We investigated the responsiveness of whole-body protein and glucose kinetics to severe trauma and the role of regulatory hormones in the early catabolic "flow phase" of injury in a group of patients ranging in age from 19 to 85. Energy metabolism (indirect calorimetry), protein kinetics (primed-constant infusion of [15N]glycine), glucose metabolism (primed-constant infusion of [U-14C]glucose and [6-3H]glucose), and circulating hormone levels were measured during basal conditions within 48 to 60 hours after injury when the patients were receiving maintenance fluids without N or calories. Experimental data were analyzed as two groups (young, age 18 to 59, and elderly, age 60 to 85) and also as linear function of advancing age. The geriatric trauma (GT) group lost less N (11.9 +/- 1.3 v 17.7 +/- 1.7 g N/d, P = .025) than the younger group, mainly due to a significantly decreased whole-body protein breakdown (WBPB) rate. Despite a similar production and oxidation rate of glucose, hyperglycemia was more exaggerated in the elderly group. Advancing age resulted in significant positive correlations with plasma glucose levels and negative correlations with circulating growth hormone levels, urinary nitrogen loss, and protein turnover. These results suggest an age- and body composition-related reduced energy and protein metabolic response to severe trauma in elderly individuals.