Total parenteral nutrition in the newborn: amino acids-energy interrelationships

As part of an ongoing study on the influence of intravenous glucose and fat on nitrogen metabolism we evaluated the relationship between the source of infused energy and plasma amino acid levels. Thirty-two studies were performed in 16 appropriate-for-gestational-age newborn infants (birth weight, 2150 +/- 115 g; means +/- SEM). In a crossover design each patient received two 6-d periods of isocaloric and isonitrogenous infusions, differing only by the source of calories (high or low fat intakes). For an energy intake of 80 kcal.kg-1.d-1 (335 kJ.kg-1.d-1) there was a significant hypoaminoacidemia (2338 +/- 185 vs 2937 +/- 196 mumol/L, high fat vs low fat) under the high-glucose intake. These data suggest that above an energy intake of 60 kcal.kg-1.d-1 (251 kJ.kg-1.d-1) there is a threshold at which changes in plasma amino acid levels are triggered by variations in the source of infused energy. Careful examination of all variables, including energy sources, is essential when aminograms are compared.