Abstract
The effects of isoflurane on myocardial oxygen uptake, metabolism and coronary blood flow (argon washin-technique) were studied in 10 patients undergoing three-vessel coronary artery bypass surgery. All patients were men with stable angina and normal left ventricular function and were receiving maintenance doses of beta-receptor antagonists or calcium channel blocking drugs. Anaesthesia consisted of isoflurane and 50% nitrous oxide in oxygen. Measurements were performed and blood samples were taken with the patients awake, 20 min after induction of anaesthesia without surgical stimulation, and during sternotomy and sternal spread. End-tidal isoflurane concentrations averaged 0.4% after induction of anaesthesia and 1.5% during sternotomy. Isoflurane significantly decreased myocardial blood flow by 18% following induction of anaesthesia, while sternotomy increased myocardial blood flow to pre-induction levels. Induction decreased myocardial oxygen uptake by 32%, while sternotomy increased oxygen uptake by 21% vs post-induction values. Myocardial uptake of glucose, lactate, free fatty acids and pyruvate significantly decreased after induction and increased to pre-induction levels during sternotomy. Myocardial lactate production, indicating myocardial ischaemia, was observed in 1 patient after induction and in three patients during sternotomy; three additional patients demonstrated a marked reduction in myocardial lactate uptake after induction and during sternotomy. It is concluded that all changes in myocardial metabolism, oxygen uptake and coronary blood flow were the result of a decrease in haemodynamic load on the myocardium and reduced contractility, while the increase in these parameters during sternotomy was due to an increase in myocardial work.(ABSTRACT TRUNCATED AT 250 WORDS)
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