Energy metabolism, substrate utilization, and nitrogen balance in parenterally fed postoperative neonates and infants. The effect of glucose, glucose + amino acids, lipid + amino acids infused in isocaloric amounts

In ten postoperative neonates and young infants the effect of three isocaloric, isovolemic intravenous nutritional regimens (glucose alone, amino acids + glucose, amino acids + lipid) on nitrogen balance, energy, and substrate metabolism were tested. Each regimen was given for 24 hours to each infant through three consecutive days, providing the same daily amino acid intake when the amino acid mixture was combined with glucose or lipid. Oxygen consumption and RQ were followed through three or four hours during each study period. The participation of three main nutrients in energy metabolism was calculated from the urinary N excretion and nonprotein RQ. Administration of glucose infusion alone was associated with a negative N balance. Addition of amino acids with glucose produced a marked N retention. This positive N balance remained unchanged when lipid was substituted for glucose as a nonprotein energy source. Alpha amino-nitrogen excretion and participation of protein catabolism in total energy metabolism were found to be identical during the three nutritional regimens, indicating that the amino acids together with glucose or lipid were either retained in nonprotein pools or were utilized for protein synthesis.