PROTEIN BALANCE IN THE FIRST WEEK OF LIFE IN VENTILATED NEONATES RECEIVING PARENTERAL-NUTRITION

Background: Protein intake is frequently delayed in ill neonates becau se of concerns about their ability to metabolize substrates. Objective : We aimed to determine the factors affecting protein balance in venti lated, parenterally fed newborns during the first week of life. Design : Leucine kinetic studies were performed in 19 neonates by using the [ 1-C-13]leucine tracer technique after 24 h of a stable total parentera l nutrition (TPN) regimen. TPN intakes were prescribed by rotating att ending physicians, enabling assessment of protein metabolism over a ra nge of clinically used nutrient intakes. Results: Mean (+/-SD) birth w eight was 1.497 +/- 0.779 kg, gestational age at birth was 30.3 +/- 4. 0 wk, and age at study was 3.9 +/- 1.4 d. Amino acid intakes (AAIs) ra nged from 0.0 to 2.9 g . kg(-1) . d(-1). Based on leucine kinetic data , protein balance was calculated as the difference between protein syn thesis and catabolism. By multiple regression analysis, AAI was the on ly predictor associated independently with protein balance (P < 0.01); energy intake, lipid intake, glucose intake, birth weight, and gestat ional age were not. Both leucine oxidation and nonoxidative leucine di sposal rates were significantly correlated with leucine intake (P < 0. 0005 and P < 0.01, respectively). Of the 12 infants with AAIs >1 g . k g(-1) . d(-1), only 1 infant was significantly catabolic (protein bala nce < -1 g . kg(-1) . d(-1)). There was no evidence of protein intoler ance as determined by elevated creatinine (69 +/- 31 mu mol/L), plasma urea nitrogen (6.7 +/- 2.53 mmol/L), or metabolic acidosis (pH: 7.36 +/- 0.05). Conclusions: Ill neonates can achieve a positive protein ba lance in the first days of life without laboratory evidence of protein toxicity.