Effect of the Quality of Infused Energy on Substrate Utilization in the Newborn Receiving Total Parenteral Nutrition

Newborn infants (n = 26), subdivided into three groups in which only the nonprotein energy was manipulated, were studied during continuously adminis- tered total parenteral nutrition. Nonprotein energy intake was provided as a glucoselfat mixture, and fat energy represented 18% (group A), 29% (group B), and 40% (group C). Energy expenditure and substrate utilization were measured by indirect calorimetry during a 6-h period. Other analyses included 24-h urinary nitrogen excretion, glycemia, and lipid profile. The results showed that glucose oxidation increased with increasing total glucose intake (p < 0.05). Net fat oxidation was observed in all groups and increased with increasing percentage of energy infused as fat. The maximal oxidative glucose disposal rate observed was in group A (11.2 g/kg/d). Maximal fat oxidation observed was in group C (2 g/kg/d), in which energy delivered by fat represented 40%. This group was more energy efficient than the others. Oxygen consumption was not affected by modification of the source of energy, but carbon dioxide production was higher in group A (p < 0.05), as was the nonprotein respiratory quotient (p < 0.05). Despite differences in carbon dioxide production, arterial capillary Pco2 was not affected and, together with the higher (p < 0.05) minute ventilation, suggests that adequate pulmonary compensation occurred during the low-fat regimen. Arterial capillary Po2 was lower during the high-fat regimen (p < 0.05). Protein oxidation was greater in group A (1.14 f 0.32 g/kg/d) than in group B (0.70 2 0.21 g/kg/d) or group C (0.78 f 0.28 g/kg/d). These data suggest that total parenteral nutrition regimens containing between 29 and 40% of calories as fat emulsion result in enhanced protein retention. (Pediatr Res 33: 11 2- 1 17, 1993) Abbreviations