Nitrous oxide does not exacerbate pulmonary hypertension or ventricular dysfunction in patients with mitral valvular disease Using the rapid-response thermistor pulmonary artery catheter and transoesophageal echocardiography, this study examined the effects of 100 per cent oxygen, 70 per cent nitrous oxide/30 per cent oxygen, and 70 per cent nitrogen/30 per cent oxygen on the pulmonary circulation and ventricular function in ten patients with pulmonary hypertension. In comparison with baseline measurements, nitrous oxide administration resulted in small but statistically significant (P less than 0.05) changes in mean arterial pressure (76 +/- 14 to 67 +/- 12), mean pulmonary arterial pressure (37 +/- 14 to 33 +/- 13 mmHg), and cardiac output (3.7 +/- 1.4 to 3.2 +/- 1.1 L.min-1). Seventy per cent nitrogen resulted in no significant changes from baseline. The repeat 100 per cent oxygen measurements were nearly identical to the nitrous oxide measurements. It is concluded that nitrous oxide does not exacerbate pulmonary hypertension or ventricular dysfunction during high-dose fentanyl anaesthesia in patients with mitral valvular disease. 