The Response of Premature Infants to Parenteral Amino Acids in the First Week of Life

This study investigated the response of premature infants to parenteral amino acids and related that response to gender, amino acid concentration at birth, amino acid status prior to infusion, postnatal age, caloric intake, weight, intake of individual amino acids, and gestational age. Plasma samples were collected from 21 premature infants (gestational age 31. 2 ± 2.3 weeks) before the initiation of amino acid infusion and after 24 hours of infusion. Mixed umbilical cord samples were available from 10 of these infants. Eleven (11) infants (gestational age 30.8 ± 2.8 weeks) receiving parenteral amino acids with no enteral supplementation were evaluated at oneweek. Plasma amino acid concentrations were compared to those reported in breast fed term infants and in preterm umbilical cord samples. Intakes were compared to published recommendations. The amino acid source was Aminosyn ( Abbott Laboratories, Chicago, Ill. ).

Neither gender, plasma amino acid concentration at birth or weight were influencing factors. Changes in concentration of most amino acids appeared to be. more a result of endogenous regulation than simple intake. Alanine infused at a high concentration showed relatively little plasma accumulation while the same concentration of glycine in the infusate lead to excessive plasma concentrations of glycine and possibly serine. Plasma concentration of histidine was high in most infants and varied directly with gestational age. Plasma phenylalanine levels varied inversely with postnatal age and tyrosine concentration varied directly with gestational age. There were indications of cysteine and taurine synthesis in some infants. Methionine intakes exceeded recommendations in all infants at one week and were associated with excessive plasma concentration. Valine concentration varied directly with caloric intake, gestational age, and valine intake. Leucine concentration also increased with gestational age from 27-33 weeks, but the relationship after that time is unclear.

The amino acid source (Aminosyn, Abbott Laboratories, Chicago, Ill.) does not appear to have ideal composition for preterm infants. For use during the first week of life when intake of both amino acids and calories is low, the infusate should contain less glycine and methionine and possibly less serine, proline, histidine, and valine.