Serum Concentrations and Urinary Excretion of Amino Acids During Total Parenteral Nutrition After Abdominal Surgery

Abstract

The effects of five days of postoperative total parenteral nutrition (TPN)—no oral intake—including a fat emulsion, Intralipid 20%, and varying amounts of amino acids and carbohydrates, on the fasting serum concentrations of amino acids, the nitrogen balance and the rate of urinary excretion of free amino acids were studied in three groups of patients, A, B and C, undergoing abdominal surgery. Group A was given 9.4 grams of nitrogen every 24 hours as 18 L-amino acids in proportions corresponding to the amino acid composition of egg protein; groups B and C were given 9.3 and 13.9 grams of nitrogen every 24 hours, respectively, including the same 18 L-amino acids in proportions corresponding to those present in human milk protein. During the first seven postoperative days, the changes in the serum concentrations of amino acids conformed largely to five patterns in all the groups. On day five, the serum concentration of methionine was higher in group B than in group C, whereas there was no difference in the urinary excretion rate for 3-methylhistidine; this suggests that an increased supply of an amino acid may be reflected in a decrease in the fasting serum concentration of this amino acid administered. During the five days of TPN, the rate of urinary excretion of glycine and histidine decreased in all the groups. The 24-hour urinary excretion of most of the amino acids administered was numerically greater in group C than in group B on all days studied with significant difference for methionine and valine on day five, whereas the excretion rate for amino acids expressed as a percentage of the total amount on a molar basis was similar for these groups. This suggests that an increase in the intravenous supply of amino acids in proportions corresponding to the amino acid composition of human milk protein is reflected in an increased rate of urinary excretion of the amino acids administered. The rate of urinary excretion of total nitrogen was similar in groups A and B. The nitrogen balance values showed efficient utilization of the two amino acids solutions studied, but no difference between them in this respect.