Branched-chain and mixed amino acid solutions and thermogenesis in postoperative patients

The effect of amino acid composition on the thermogenic response to amino acid infusion was studied in 20 spontaneously breathing postoperative coronary bypass patients and 6 healthy volunteers. On the 1st postoperative day, patients received either a balanced amino acid solution (2510 kJ/24 h) or an amino acid solution consisting primarily (88.8%) of branched-chain amino acids (BCAAs; 2510 kJ/24 h) for 6 h. Another group of patients receiving only hypocaloric glucose served as control subjects. The volunteers randomly received the same balanced amino acid solution (2510 kJ/24 h) or the same BCAA-enriched solution (2510 kJ/24 h) for 6 h. In the coronary bypass patients, both infusion regimens resulted in an increase in resting energy expenditure (REE) (p < 0.01). The thermogenic response to nutrition was 28.5 +/- 5.8 and 46.9 +/- 4.3% (mean +/- SE) in the patients receiving the balanced and BCAA-enriched solutions, respectively (p < 0.05). REE did not change in the control group. Alveolar ventilation increased in both groups (p < 0.05), and the change was more prominent in patients receiving the BCAA-enriched solution. PaCO2 decreased significantly in both nutrition groups. In the healthy subjects, REE increased only during the balanced amino acid infusion (p < 0.05). The thermogenic response to the balanced amino acid solution was 20.7 +/- 4.2% (p < 0.05), whereas no thermogenic response to the BCAA-enriched solution was observed (-5.6 +/- 3.3%, NS). This difference was probably due to the smaller energy cost of BCAA metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)