Haemodynamic response to nitrous oxide during high-dose fentanyl pancuronium anaesthesia

Ten patients subjected to coronary by-pass surgery were studied to determine the haemodynamic effects of replacing Fio2 1.0 normoventilation with nitrous oxide in oxygen (Fio2 0.3) after induction of anaesthesia with fentanyl (50 micrograms/kg), flunitrazepam and pancuronium. In all patients the application of N2O decreased systemic arterial pressures by an average of 10% (P less than 0.001), but left pulmonary arterial pressures and systemic vascular resistance unchanged. The slight bradycardia induced was associated with moderate depression of the cardiac index and the left ventricular stroke work index (P less than 0.001) at the time when the rate-pressure product was decreased by 20% (P less than 0.001). The cardiac depression produced by N2O was most prominent in patients with left ventricular wall hypokinesia and an ejection fraction below 55%, in whom the cardiac work index was diminished by 29%. The replacement of oxygen with nitrous oxide in oxygen during high-dose fentanyl-pancuronium anaesthesia seems not to be associated with sympathetic stimulation, and the myocardial depressant effect of N2O should be weighed against the possible reduction in myocardial oxygen consumption with special care in patients with compromised myocardial function.