Thermogenic effect of amino acids not demonstrated in heart surgery with cardiopulmonary bypass.

BACKGROUND: In abdominal surgery and in healthy volunteers, amino acids increased thermogenesis. In this double-blind study we investigated if a similar effect would ensue in heart surgery and accelerate the rewarming process postoperatively. METHODS: Thirty-four patients undergoing coronary artery bypass grafting or aortic valve replacement were randomized into two groups, and received either 500 ml of amino acids or Ringer's solution intravenously during 4 h. The infusion was started approximately 30 min before the end of a cardiopulmonary bypass (CPB), performed at a temperature of 34 degrees C with rewarming to 36-37 degrees C. The lowest pulmonary artery (PA) temperature after the CPB and the time interval until the temperature reached 37 degrees C were recorded. Oxygen uptake was calculated from cardiac output (thermodilution) and the pulmonary av-difference of oxygen after induction of anaesthesia, at the end of surgery, and 1 and 2 h after the CPB. RESULTS: Demographic data, medication including beta-blockers, CPB data and case mix were similar. The lowest temperature after the CPB was 35.9 +/- 0.1 degrees C in the amino acid group and 35.6 +/- 0.2 degrees C in the control group, and the increase per hour was 0.6 +/- 0.1 degrees C and 0.6 +/- 0.0 degrees C, respectively, with no differences between the groups. During the infusion, oxygen uptake was higher in the amino acid group, 115 +/- 4 ml m(-2), than in the controls, 102 +/- 3 ml m(-2) (P < 0.05). No adverse effects of the infusions were noted. CONCLUSION: The lack of a thermal effect of the amino acids in the heart surgery was most probably due to the temperature gradients between the different body compartments, and also may have been due to the use of beta-blockers.

[Amino acid administration counteracts hypothermia during anesthesia]. / Aminosyretillförsel motverkar hypotermi under anestesi.

General anesthesia induces hypothermia due to decreased metabolic rate and impaired thermoregulation. Adverse effects of hypothermia are common. Many warming devices are in use to prevent heat loss, but little attention has been paid to stimulating the body's own heat generation. NIT, nutrient-induced thermogenesis, signifies the concept that all nutrients raise energy expenditure. The greatest thermic effect is ascribed to amino acids and proteins, 30-40%. During anesthesia the thermogenic effect of i.v. amino acids was increased. The results support the existence of an inhibitory action normally exerted by central thermosensors in order to prevent hyperthermia. During anesthesia, central thermosensors are impaired, and hence amino acid thermogenesis is exaggerated, which may prevent hypothermia.

Amino acid-induced thermogenesis reduces hypothermia during anesthesia and shortens hospital stay.

UNLABELLED: Amino acid infusion during general anesthesia induces thermogenesis and prevents postoperative hypothermia and shivering. We propose that amino acid prevention of hypothermia during anesthesia shortens the hospital stay. Core temperatures and pulmonary oxygen uptake were measured in 45 patients, receiving an IV amino acid mixture, 126 mL/h, before and/or during isoflurane anesthesia and 30 control patients receiving acetated Ringer's solution. At awakening, mean core temperature was 36.5 degrees+/-0.1 degrees C in the amino acid group and 35.7 degrees+/-0.1 degrees C (P < 0.001) in the controls. Energy expenditure increased by 54%+/-9% from baseline in amino acid patients in whom shivering was uncommon, but only by 5%+/-4% (P < 0.001) in control patients, of whom the majority developed postoperative shivering. The estimated difference in hospital stay between the two groups was 2.7 days (CI 95%: 1.3-4.0). Multiple regression analysis showed that the variables best predicting hospitalization were duration of surgery, amino acid treatment, and awakening temperatures. Duration of surgery was similar in the two groups and core temperatures at awakening were a result of amino acid infusion, which indicates that amino acid infusion during anesthesia and surgery was the most important factor for the shorter hospitalization. IMPLICATIONS: Amino acid infusion during general anesthesia induces thermogenesis and prevents postoperative hypothermia and shivering. Multiple regression analysis indicated that this resulted in a shorter hospital stay.

Amino acid-induced thermogenesis to prevent hypothermia during anesthesia is not associated with increased stress response.

UNLABELLED: Intraoperative infusion of amino acids stimulates oxygen uptake with a resulting increase in heat production, especially during emergence from anesthesia. To determine whether the increased thermogenesis in response to amino acid infusion during and after anesthesia induces any additional stress in surgical patients, plasma catecholamines were measured. Fourteen patients aged 44+/-15 yr scheduled for gall bladder surgery during isoflurane anesthesia were studied. Seven patients received an IV amino acid infusion at the rate of 126 mL/h throughout anesthesia, and seven control subjects received equal volumes of nutrient-free saline. At five defined times during and after anesthesia, arterial adrenaline and noradrenaline concentrations were determined. Arterial blood pressure and heart rate were recorded simultaneously. There were considerable variations from baseline in levels of plasma adrenaline and noradrenaline, heart rate, and blood pressure during the study period, but there were no significant differences between the two groups at any time throughout anesthesia and surgery. In conclusion, the augmented thermogenic effect of amino acids during and at emergence from anesthesia is suggested to occur without imposing any additional stress in the surgical patient. IMPLICATIONS: Amino acid infusion during anesthesia has been demonstrated to markedly increase oxygen consumption and heat production. To determine whether this evokes any stress in the patients, we measured plasma catecholamines during anesthesia. We suggest that temperature preservation during anesthesia by an amino acid infusion occurs without additional sympathoadrenal activity.

Postoperative nitrogen excretion after amino acid-induced thermogenesis under anesthesia.

UNLABELLED: Amino acid infusions during general anesthesia induce thermogenesis and prevent postoperative hypothermia. The effects of increased heat production during anesthesia on postoperative nitrogen balance have not been examined. Therefore, we studied the effect of perioperative amino acid infusions on postoperative nitrogen excretion in 24 patients scheduled 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 received an IV amino acid mixture, 240 kJ/h, before and during anesthesia. Rectal temperature and energy expenditure were measured. The urinary nitrogen content was calculated from urea, creatinine, and urate the day before surgery and for 4 days postoperatively. Diets were recorded. In anesthetized control patients, postoperative nitrogen excretion was less than preoperative levels. Those patients also experienced the largest 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 pronounced (1.0+/-0.1 degrees C; P < 0.001) and postoperative shivering disappeared. In addition, the nitrogen excretion was unchanged postoperatively, perhaps indicating an increase in protein turnover known to generate heat. In conclusion, the increase in heat production induced by amino acids reduced hypothermia, abolished shivering, and attenuated/normalized the postoperative nitrogen saving that occurred in patients who did not receive amino acids. IMPLICATIONS: We compared nitrogen excretion 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 shivering, and attenuated/normalized the postoperative nitrogen saving that occurred in patients who did not receive amino acids.

Augmented thermic effect of amino acids under general anaesthesia occurs predominantly in extra-splanchnic tissues.

1. Intravenous infusion of amino acid mixtures stimulates human oxidative heat production more effectively under general anaesthesia than in the unanaesthetized state. To analyse the splanchnic and extra-splanchnic regional distribution of this stimulation, whole body and splanchnic oxygen uptake, blood flow and blood temperatures were measured by a catheterization technique in 14 patients undergoing isoflurane anaesthesia for abdominal surgery. During the anaesthesia period, a mixture of 19 amino acids (240 kJ/h) was infused intravenously into seven of the patients while the others served as controls, receiving isovolumic infusions of a nutrient-free saline solution. 2. Whole body oxygen consumption fell by approximately 40% during anaesthesia and surgery in the controls. Approximately 80-95% of the reduction occurred in the extra-splanchnic tissues. The splanchnic oxygen uptake fell by 31 +/- 6% in the controls during the initial phase of anaesthesia, after which it returned to the pre-anaesthesia level. The initial reduction of the controls' splanchnic oxygen consumption accounted for only approximately 23% of the simultaneous anaesthesia-induced reduction in pulmonary oxygen uptake. No initial reduction of the splanchnic oxygen uptake was observed in the patients treated with amino acid. 3. The amino acid infusion stimulated the whole body oxidative heat production by approximately 18 W during anaesthesia and surgery and by approximately 70 W at the emergence from anaesthesia. Approximately 74% of the stimulation occurred in the extra-splanchnic tissues. At awakening, the splanchnic oxygen uptake rose to approximately 64% above the pre-anaesthesia level in the amino acid group. 4. During the entire period of anaesthesia, the whole body heat content fell by 282 +/- 68 kJ in the controls and by 57 +/- 25 kJ in the amino acid group. Amino acid treatment thus prevented approximately 80% of the anaesthesia-induced reduction in whole body heat content. 5. During anaesthesia and surgery, cardiac output was approximately 25% and approximately 16% below the baseline, preanaesthesia levels in the control and amino acid groups, respectively. At awakening, it rose to approximately 44% above baseline in the amino acid group while in the controls it remained unchanged. In both groups the splanchnic blood flow was unaffected by anaesthesia or by amino acid infusions.

Preoperative infusion of amino acids prevents postoperative hypothermia.

Intraoperative infusion of amino acids has been found to stimulate energy expenditure and thereby prevent anaesthesia-induced hypothermia. Rectal temperature and respiratory gas exchange were measured in 24 female patients before and after isoflurane anaesthesia. Sixteen patients had an amino acid mixture of 240 kJ h-1, infused over 1-2 h before anaesthesia and eight control patients received saline. We compared the results with data from six female volunteers treated with amino acids; they were not premedicated or anaesthetized. In lorazepam premedicated patients, amino acids increased the pre-anaesthesia temperature by 0.3 degrees C h-1, twice that observed in the volunteers. At awakening after anaesthesia, energy expenditure increased to 50-60% above baseline in the amino acid treated patients, while in the control patients, receiving saline, no increase occurred, despite vigorous shivering. Amino acid infusion prevented hypothermia by increasing heat accumulation and causing delayed stimulation of heat production. The heat accumulation response to amino acid infusion was increased after premedication with lorazepam.

Augmented thermic effect of amino acids under general anaesthesia: a mechanism useful for prevention of anaesthesia-induced hypothermia.

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)