Anaesthesia for abdominal aortic surgery in patients with coronary artery disease, part II: effects of nitrous oxide on systemic and coronary haemodynamics, regional ventricular function and incidence of myocardial ischaemia

This study examines the effects of nitrous oxide on haemodynamics, anterior left ventricular (LV) function and incidence of myocardial ischaemia in abdominal vascular surgical patients with coronary artery disease. Forty-seven patients were randomly assigned to isoflurane-fentanyl anaesthesia with nitrous oxide-oxygen vs air-oxygen (control). Systemic and coronary haemodynamics, 12-lead ECG, LV anterior wall motion by cardiokymography (CKG) and myocardial lactate balance were recorded at four intervals: before and during anaesthesia and 10 and 30 minutes into surgery. Systemic haemodynamics were controlled by anaesthetic dose, and, when insufficient, by i.v. nitroglycerine (NG) in case of LV failure (PCWP > 18 mmHg) and by phenylephrine during hypotension. We found that nitrous oxide was associated with greater need for i.v. nitroglycerin (patients: P = 0.031, episodes P = 0.005) and more myocardial ischaemia (patients P = 0.012, episodes P = 0.001) despite systemic and coronary haemodynamics comparable to the control group. We conclude that nitrous oxide, known to have both sympathomimetic and cardiodepressive actions, produced cardiodepression in the face of sympathetic stimulation. Our study design did not allow to conclude if myocardial ischaemia was the consequence of increased wall stress or a reason for the observed LV dysfunction. The higher incidence of introperative myocardial ischaemia and need for NG did not cause increased cardiac morbidity.