Metabolic, thermal and circulatory effects of intravenous infusion of amino acids in tetraplegic patients.

Metabolic, circulatory and thermal effects of intravenously (i.v.) administered amino acids were studied in eight patients with complete cervical spinal cord injuries, and compared with the effects in eight healthy subjects. Using indirect calorimetry and catheter techniques, whole-body and splanchnic oxygen consumption, blood flow and blood temperatures were measured before and at timed intervals during 2.5 h of i.v. infusion of 600 kJ of a mixture of 19 amino acids. Pulmonary oxygen uptake increased from 209 +/- 11 to 267 +/- 13 ml min-1 in the patients and from 268 +/- 5 to 320 +/- 8 ml min-1 in the controls. The thermic effect of amino acids was 21 +/- 3% and 16 +/- 2% in patients and controls, respectively. In both groups the splanchnic tissues accounted for approximately half of the rise in whole-body oxygen consumption. Cardiac output rose by, on average, 0.5 +/- 0.1 and 0.8 +/- 0.2 1 min-1 in patients and controls, respectively, while the hepatic blood flow remained unchanged in both groups. Pulmonary arterial blood temperature increased by 0.647 +/- 0.100 degrees C in the patients and by 0.244 +/- 0.174 degrees C in the controls (P < 0.05). The whole-body specific heat was low in the patients, its calculated maximum value being approximately 20% below the normal level. During the amino acid infusion the arterial blood concentration of amino acids rose by approximately 170% and 112% of its basal levels in patients and controls, respectively, indicating a significantly reduced capacity for cellular uptake of amino acids in tetraplegic patients. It is concluded that, in tetraplegic patients, i.v. infused amino acids induce prompt thermogenesis of normal magnitude accompanied by supranormal temperatures and amino acid concentrations in the blood, and that low whole-body specific heat contributes to the well-known thermoregulatory instability in tetraplegia.