Augmented Thermic Effect of Amino Acids under General Anaesthesia: A Mechanism Useful for Prevention of Anaesthesia-Induced Hypothermia

Abstract

1. Intravenous infusion of amino acids stimulates energy expenditure and heat accumulation in normal man. To find out whether such stimulation also occurs during general anaesthesia, thermogenesis was measured in 21 patients before, during and after anaesthesia and surgery. 2. Ten patients received a mixture of 19 amino acids (240 kJ/h) infused intravenously throughout the anaesthesia. The other 11 patients, serving as controls, received saline. Using catheters previously inserted into the pulmonary and a systemic artery, cardiac output, arteriovenous oxygen difference, pulmonary oxygen uptake and mixed blood temperature were measured. 3. During anaesthesia and surgery, the blood temperature fell by 0.67 +/- 0.09 degrees C/h in the control patients and by 0.38 +/- 0.06 degrees C/h in the amino acid-treated patients. Anaesthesia during 34 +/- 4 min before surgery reduced the pulmonary oxygen uptake by 145 +/- 9 ml/min in the control patients and by 81 +/- 10 ml/min in the amino acid-treated patients, corresponding to reductions in total energy expenditure of 47 W in the control group and 26 W in the amino acid-treated group. The difference, 21 W, illustrates the thermogenic action of the amino acids. This value may be compared with that of 4 W, observed in unanaesthetized individuals subjected to 30 min of identical amino acid infusions. 4. At awakening after the anaesthesia, the oxygen consumption rose to 71 +/- 21% above the pre-anaesthesia level in the amino acid-treated patients, who, without shivering, rapidly returned to normothermia, whereas in the control patients the oxygen uptake remained slightly below the pre-anaesthesia level, despite sustained hypothermia and vigorous shivering.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of Myofibrillar Proteolysis Following Infusion of Amino Acid Mixture Correlates Positively with Elevation of Core Body Temperature in Rats

“…In fact, plasma MeHis concentrations that would reflect increased protein turnover as discussed above displayed good correlations with rectal temperature under both anesthetic and conscious conditions. Furthermore, it is well known that AA administration increases oxygen consumption and elevates Tb under both conscious and anesthetized conditions (1)(2)(3)6). These findings therefore indicate that increased protein turnover in rats given AA contributes to increased metabolic heat production, resulting in elevated Tb.…”

Bolus Oral or Continuous Intestinal Amino Acids Reduce Hypothermia during Anesthesia in Rats

“…The heat production from infusion of amino acids is markedly increased during anesthesia and reduces the degree of hypothermia at emergence from anesthesia (4-6, 9, 10). The underlying mechanisms may be explained incompletely, and hence discussed by several authors (4,7,10,14,15). Most probably there is a combination of thermoregulatory and molecular factors.…”

Amino Acids during Perioperative Period

“…The elevation in both synthesis and degradation rate of amino acids in the skeletal muscle provide collateral evidence of the critical role of elevated turnover in muscular protein metabolism, well known to generate heat. During anesthesia, when thermoregulation is impaired and the central inhibitory pathway in metabolism is depressed, the heat production in this process is increased compared to the awake state [4]. Another finding suggesting a key role of skeletal muscle as an organ for thermogenesis, was that infusion of amino acid mixture showed no effect on hypothermia in a rat model of skeletal muscle atrophy [34].…”