Pulmonary Vascular Responses to Nitrous Oxide in Patients with Normal and High Pulmonary Vascular Resistance

Abstract

The pulmonary vascular responses to 50% N2O were studied in 32 anesthetized patients ventilated to maintain normal PaCO2 [arterial CO2 torsion]. One group consisted of 16 patients with coronary artery disease (CAD) and normal pulmonary vascular resistance (PVR) about to undergo coronary artery bypass surgery. A 2nd group consisted of 16 patients with markedly elevated PVR values due to chronic mitral valve stenosis (MVS). CAD patient showed a significant increase in PVR irrespective of whether halothane or fentanyl was used as background anesthetic. Individual changes did not exceed the upper limit of normal and are not of clinical importance in these patients. In patients with MVS subjected to fentanyl anesthesia. N2O caused a marked increase in PVR from 357 to 530 dyn.cntdot.s.cntdot.cm-5. Halothane anesthesia did not significantly attenuate the effect of N2O on the pulmonary vasculature as mean PVR increased from 351 to 451 dyn.cntdot.s.cntdot.cm-5. Evidently, the preexisting PVR value is of more importance for the pulmonary vascular response to N2O than the influence of background anesthesia. Evidently, N2O should be used with caution in patients with elevated PVR, particularly in the presence of right ventricular dysfunction and/or right CAD.