Ratio of non-protein calories to grams of amino acids and amino acid blood levels in preterm infants receiving parenteral nutrition

BackgroundStudies evaluating the optimal intake of amino acids for preterm infants have often not considered the effect of the non-protein calorie to grams of amino acids ratio (NPKcal:g AA) in parenteral nutrition solutions. The objectives of this study were to document the ratio in a group of preterm infants and explore any associations of the ratio to AA and acylcarnitine levels.MethodsThis was descriptive cohort study of data collected from a previously published prospective study evaluating the influence that gestational age had on amino acid and acylcarnitine profiles in preterm infants ≤31 weeks postmenstrual age. Acylcarnitine and AA levels on day of life 7 of three study groups, based upon terciles of the NPKcal:g AA, who were receiving minimal enteral feedings and an enterally fed comparison group were measured. Growth velocities and changes in z-scores were also evaluated.ResultsNPKcal:g AA terciles were: 6.3-17.6:1 (low, <i>N</i> = 153), 17.7-21.2:1 (mid, <i>N</i> = 150), and 21.3-36.2:1 (high, <i>N</i> = 159). Higher levels of ornithine, citrulline, blood urea nitrogen, isovalerylcarnitine + methylbutyrylcarnitine, and octenoylcarnitine were found in the low versus the high group. From day 1-42 of life, the low group had a lower head circumference (HC) growth velocity and the low and mid groups had more negative HC changes in z-scores versus the enteral group.ConclusionsThis study suggests that preterm infants may receive parenteral nutrition solutions containing inadequate energy to prevent oxidation of administered AA. The impact of inadequate non-protein caloric intake needs to be considered when evaluating growth and outcomes in nutritional studies of VLBW infants.