Haemodynamic Response to Nitrous Oxide during High-Dose Fentanyl Pancuronium Anaesthesia

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Abstract
Patients (10) subjected to conronary bypass surgery were studied to determine the hemodynamic effects of replacing FiO2 [fractional inspiratory O2] 1.0 normoventilation with N2O in O2 (FiO2 0.3) after induction of anesthesia with fentanyl (50 .mu.g/kg), flunitrazepam and pancuronium. In all patients the application of N2O decreased systemic arterial pressure by an average of 10% (P < 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 < 0.001) at the time when the rate-pressure product was decreased by 20% (P < 0.001). The cardiac depression produced by N2O was most prominent in patients with left ventricular wall hypokinesia and a ejection fraction below 55%, in whom the cardiac work index was diminished by 29%. The replacement of O2 with N2O in O2 during high-dose fentanyl-pancuronium anesthesia seems not to be associated with sympathetic stimulation, and the myocardial depressant effect of N2O should be weighed against the possible reduction in myocardial O2 consumption with special care in patients with compromised myocardial function.