Coronary Haemodynamic Effects of Surgery during Enflurane‐Nitrous Oxide Anaesthesia in Patients with Ischaemic Heart Disease

Abstract

The systemic and coronary haemodynamic effects of 1.5 MAC enflurane-nitrous oxide anaesthesia and abdominal surgery were investigated in nine patients with ischaemic heart disease. Anaesthesia decreased systemic blood pressure (-56%) by a combination of cardiodepression and peripheral vasodilation. A marked fall in myocardial oxygen extraction suggested a moderate coronary vasodilation. Surgery markedly increased the circulating levels of adrenaline and noradrenaline, manifested by increases in blood pressure (+76%) and systemic vascular resistance (+83%). Pulmonary capillary wedge pressure increased by 70% without any change in cardiac or stroke volume index, suggesting that the patients were performing at the horizontal part of their left ventricular function curve. Despite the marked rise in coronary perfusion pressure and a 62% increase in myocardial oxygen demand, coronary blood flow remained unaltered. This could be due either to coronary vasoconstriction overriding the normal coronary autoregulation or to an increase in coronary back pressure opposing the diastolic aortic pressure. When coronary blood flow could not increase to meet the demand for oxygen, the myocardium had to extract more oxygen to ensure appropriate oxygenation, demonstrating interference with coronary autoregulation. Surgery markedly increased myocardial extraction of adrenaline and noradrenaline. We could not find any relationship between myocardial adrenaline extraction and heart rate response to surgery or between myocardial noradrenaline extraction and changes in coronary blood flow, calculated coronary vascular resistance, incidence of myocardial ischaemia or cardiac dysrhythmias.