Characteristics of protein sparing effect of total parenteral nutrition in the surgical infant.

To determine the best formula to prevent protein depletion, 31 surgical infants on intravenous (IV) diet were studied. The study was divided into two phases. Phase I diet included 5% glucose and 1.5% or 2% amino acid infusion; phase II diet consisted of 5% glucose and 1.5% or 2% aminoacid plus 10% Intralipid. In each phase, oxygen consumption, carbon dioxide production, and energy expenditure were determined. The utilization of carbohydrate, fat, and protein was calculated from urinary nitrogen excretion and nonprotein respiratory quotient. The mean caloric intake during phase I and phase II was 62 and 94 kcal/kg/d, respectively. A positive nitrogen balance was obtained in infants receiving fat-free total parenteral nutrition (TPN) with a mean protein intake of 2.6 g/kg/d and a mean energy intake exceeding the energy expenditure by 24%. Infusion of more calories as Intralipid (phase II) caused a significant reduction in protein oxidation, thus protein contribution to the energy expenditure and an increase in protein retention. We conclude that supplementation of low-calorie TPN diets with Intralipid increases protein sparing and is preferable to the administration of very high glucose loads.