NON-PROTEIN CARBON BALANCE, GULCOSE AND FAT UTILISATION IN TERM INFANTS ON FAT-FREE PARENTERAL NUTRITION

Abstract

Glucose is the main energy source for infants on total parenteral nutrition. In order to study the impact of increasing levels of glucose intake we performed continuous open circuit indirect calorimetry during 4 hrs on 38 AGA term infants. The energy intakes ranged between 13.1 and 105.0 kcal/kg.d and the glucose intakes between 3.5 and 24.1 g/kg.d Glucose oxidation increased significantly with increasing glucose intake (r=0.90; p<0.001), but was only 80% of the intake at all levels of intake up to 24 g/kg.d. Endogenous fat oxidation decreased significantly with increasing energy intake (r=-0.80; p<0.001) and with increasing glucose oxidation (r=-0.95; p<0.001). The increase in glucose intake resulted in a significant increase in energy expenditure (r=0.82; p<0.001), in non-protein carbon dioxide production (r=0.87); p<0.001) and non-protein oxygen consumption (r=0.66; p<0.001). Non-protein carbon balance was negative at low glucose intakes becoming positive with increasing levels of glucose infusion.

CONCLUSIONS: 1) Indirect calorimetry shows no upper limit in glucose oxidation in newborn infants on fat-free parenteral nutrition. 2) 1/5 of the glucose carbon atoms are stored as fat, glycogen or in an unidentified tissue carbon pool (e.g.: glycerol, cholesterol, non-essential amino acids, glycoproteins, etc.), depending on the level of energy intake. 3) At high glucose intakes, there is increasing lipogenesis which wastes energy and produces more carbon dioxide than it consumes oxygen; this might impose a respiratory stress on the neonate with borderline lung function.

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