THE INDEPENDENT METABOLIC EFFECTS OF HALOTHANE AND ISOFLURANE ANESTHESIA

Twelve healthy, unpremedicated women scheduled for total abdominal hys terectomy were given either isoflurane (n = 6) or halothane (n = 6) an aesthesia. They all received general anaesthesia for a period of 3 h, with surgery being carried out only in the last hour. The anaesthesia consisted of thiopentone, pancuronium and a mixture of oxygen-enriched air (Fio2=34%) supplemented with 1 MAC of either isoflurane or haloth ane. The patients were maintained normothermic, and with an arterial S ao2 above 95% throughout the period of the study. The following measur ements were made before, during and after anaesthesia (with and withou t surgery): oxygen consumption (Vo2), carbon dioxide production (Vco2) ; circulating concentrations of various hormones (insulin, growth horm one and cortisol); various metabolites; selected amino acids and album in; forearm arterio-venous concentration difference of glucose, lactat e, free fatty-acids and selected amino acids (four patients in each gr oup). Whole body Vo2 decreased significantly by over 20% during anaest hesia (with or without surgery), P < 0.05). Although the circulating c oncentration of most amino acids showed little or no change during ana esthesia alone, there was a tendency for the flux of most metabolites to decrease, and this persisted during surgery (P < 0.05). During anae sthesia alone there was a twofold reduction in the plasma cortisol con centration (P < 0.05), and a decrease in albumin concentration (P < 0. 01). With the onset of surgery, plasma cortisol concentration increase d rapidly (in association with several other hormones and metabolites) but hypoalbuminemia persisted.