Effects of postoperative infusion of branched chain amino acids on nitrogen balance and forearm muscle substrate flux.

A branched chain amino acid (45% BCAA)--enriched solution was compared with a standard amino acid (25% BCAA) solution in a randomized blinded study in eight patients undergoing cystectomy and ileal loop diversion. Solution administration rates were designed to provide 20 kcal/kg/day and 0.26 gm nitrogen/kg/day postoperatively from days 1 to 8. Daily urine creatinine and nitrogen levels were measured. On day 4 during infusion, forearm blood flow was measured by capacitance plethysmography. Arterial and antecubital deep venous blood samples were drawn simultaneously for determinations of glucose, lactate, pyruvate, and amino acids; substrate flux was calculated (mumol/ml/min, uptake = +, release = -). The mean total amino acid flux was significantly improved In the 45% BCAA group (+1.7 +/- 0.4) versus the 25% BCAA group (-0.03 +/- 0.2, P less than 0.05). The mean total BCAA flux was significantly improved in the 45% BCAA group (+1.1 +/- 0.4) compared with the 25% BCAA group (-0.03 +/- 0.2) (P less than 0.02). There were no significant differences between groups in alanine, glutamine, glucose, lactate, or pyruvate forearm flux. The cumulative adjusted 7-day nitrogen balance was -1.4 +/- 7 gm in the 45% BCAA group and -14.2 +/- 4 gm in the 25% BCAA group (NS). the 45% BCAA solution resulted in significant uptake of total amino acid and BCAA into forearm muscle, which was not significantly demonstrated in whole body nitrogen balance studies. Sixty-six percent of the increase in total amino acid forearm flux with use of the 45% BCAA solution was due to the uptake of BCAA even though less leucine was given compared with the 25% BCAA solution.