Pulmonary and systemic vascular responses to nitrous oxide in patients with mitral stenosis and pulmonary hypertension.

Pulmonary and systemic circulatory responses to inhalation of 50% nitrous oxide were studied in 11 patients with pulmonary hypertension prior to elective mitral valve replacement. All patients were premedicated with intramuscular morphine and scopolamine. Compared with awake control measurements while breathing 50% oxygen in nitrogen, heart rate, cardiac index, systemic and pulmonary vascular pressures, systemic vascular resistance, and systemic and pulmonary heart rate, systolic blood pressure products remained unchanged after administration of 50% nitrous oxide for 10 minutes. The only significant change was an increase in pulmonary vascular resistance from 159 +/- 18 dynes.sec.cm-5 before nitrous oxide inhalation to 213 +/- 27 dynes.sec.cm-5 during nitrous oxide inhalation (p less than 0.05). We conclude that nitrous oxide increases pulmonary vascular resistance in patients with preexisting pulmonary hypertension; however, this increase is not associated with alterations in other measured or calculated hemodynamic variables and is probably not of sufficient magnitude to recommend avoiding nitrous oxide in these patients.