POSTOPERATIVE NITROGEN-EXCRETION AFTER AMINO ACID-INDUCED THERMOGENESIS UNDER ANESTHESIA

Amino acid infusions during general anesthesia induce thermogenesis an d prevent postoperative hypothermia. The effects of increased heat pro duction during anesthesia on postoperative nitrogen balance have not b een examined. Therefore, we studied the effect of peri operative amino acid infusions on postoperative nitrogen excretion in 24 patients sch eduled for hysterectomy. Seven volunteers not subjected to anesthesia or surgery were used as awake controls. During isoflurane anesthesia, 8 patients received acetated Ringer's solution, and 16 patients receiv ed an TV amino acid mixture, 240 kJ/h, before and during anesthesia. R ectal temperature and energy expenditure were measured. The urinary ni trogen content was calculated from urea, creatinine, and urate the day before surgery and for 4 days postoperatively. Diets were recorded. I n anesthetized control patients, postoperative nitrogen excretion was less than preoperative levels. Those patients also experienced the lar gest decrease in core body temperature during anesthesia (1.7 +/- 0.1 degrees C). All had postoperative shivering. In the amino acid-treated patients, the temperature decrease during anesthesia was less pronoun ced (1.0 +/- 0.1 degrees C; P < 0.001) and postoperative shivering dis appeared. Ln addition, the nitrogen excretion was unchanged postoperat ively, perhaps indicating an increase in protein turnover known to gen erate heat. Ln conclusion, the increase in heat production induced by amino acids reduced hypothermia, abolished shivering, and attenuated/n ormalized the postoperative nitrogen saving that occurred in patients who did not receive amino acids. implications: We compared nitrogen ex cretion before and after surgery in patients who received a saline or amino acid infusion during isoflurane anesthesia. The increase in heat production induced by amino acids reduced hypothermia, abolished shiv ering, and attenuated/normalized the postoperative nitrogen saving tha t occurred in patients who did not receive amino acids.