Amino acid infusion induces thermogenesis and reduces blood loss during hip arthroplasty under spinal anesthesia

The thermic effect of amino acids is augmented under general anesthesia and counteracts hypothermia. Mild hypothermia may increase surgical bleeding. We studied whether amino acids also induce thermogenesis under spinal anesthesia and whether this endogenous heat production reduces bleeding during hip arthroplasty. Rectal temperature, oxygen uptake, and perioperative bleeding were measured in 22 patients receiving an IV amino acid mixture (Vamin 18), 240 kJ/h) for 1 h before and then during spinal anesthesia and in 24 control patients receiving acetated Ringer's solution. Blood loss was calculated after surgery by weighing the swabs and the content of the suction tubes after subtraction of the saline used. After surgery, the closed drains were weighed after 24 h. In the amino acid group, the preanesthesia temperature increased by 0.4 degrees C +/- 0.2 degrees C (P < 0.01) and was unchanged in controls. At end of surgery, core temperature had decreased by 0.9 degrees C +/- 0.4 degrees C in controls and by 0.4 degrees C +/- 0.3 degrees C in the amino acid patients (P < 0.01). Oxygen uptake increased by 26 +/- 7 mL/min, or 16% +/- 5% (P < 0.05), from baseline in the amino acid patients, whereas it was unchanged in the controls. Blood loss during surgery was significantly larger in the control patients (702 +/- 344 mL) than in the amino acid patients (516 +/- 272 mL) (P < 0.05). After surgery, there were no significant differences in shed blood volume. In conclusion, amino acid infusion also induced a thermogenic response under spinal anesthesia. In addition, the prevention of temperature decrease during spinal anesthesia seemed to have a positive effect on intraoperative blood loss. IMPLICATIONS: Infusion of a balanced mixture of amino acids during spinal anesthesia prevented core body temperature decrease. Bleeding was also less pronounced.