Protein and energy balance following femoral neck fracture in geriatric patients

Abstract

To elucidate the effect of total peripheral parenteral nutrition (TPPN) on protein kinetics following injury, we compared the whole-body leucine kinetic response using a primed-constant infusion of l-[1- 14C]leucine in 33 elderly patients (aged 82 ± 1.0 years) following hip fracture and 33 healthy elderly control subjects (aged 75 ± 0.7 years). Following a 36-hour fast, leucine release from protein breakdown was 1.2 ± 0.10 μmol · kg −1 · min −1 and leucine incorporation into protein was 0.94 ± 0.095 μmol · kg −1 · min −1 in control subjects, and in injured subjects leucine release from protein breakdown was 1.3 ± 0.14 μmol · kg −1 · min −1 and leucine incorporation into protein was 0.97 ± 0.092 μmol · kg −1 · min −1. Control and injured subjects were then administered TPPN (protein, 1.5 g amino acids · kg −1; carbohydrate, 10.0 kcal · kg −1; lipid, 15.0 kcal · kg −1) for 24 hours, and leucine kinetics were redetermined. Compared with protein kinetics in the fasting state, leucine release from protein decreased to 1.0 ± 0.14 μmol · kg −1 · min −1 and leucine incorporation into protein increased to 1.16 ± 0.097 μmol · kg −1 · min −1 in control subjects. Injured patients also responded to TPPN with a decrease in leucine release from protein breakdown (1.12 ± 0.156 μmol · kg −1 · min −1) and an increase in leucine incorporation into protein (1.29 ± 0.164 μmol · kg −1 · min −1). These results indicate that in a geriatric population, whole-body leucine kinetics following hip fracture and the anabolic response to TPPN are not significantly altered from those of uninjured subjects. The overall metabolic response of energy expenditures and efficiency of nitrogen retention does suggest a mild catabolic response that may be reversed by nutritional intervention.