Effects of inhaled nitric oxide in patients with hypoxemia and pulmonary hypertension after cardiac surgery

Abstract

Background: Cardiopulmonary bypass can increase pulmonary vascular tone and decrease ventilation-perfusion matching by impairing the pulmonary endothelial production of nitric oxide.

Objectives: We tested the hypothesis that inhalation of exogenous nitric oxide decreases the ratio of mean pulmonary arterial pressure to mean system arterial pressure and the intrapulmonary shunt fraction and increases the ratio of arterial blood oxygen tension to fraction of inspired oxygen in patients in whom the ratio of mean pulmonary arterial pressure to mean systemic arterial pressure is more than 0.50, and the ratio of arterial blood oxygen tension to fraction of inspired oxygen is less than 300 mm Hg in the first 24 hours after cardiopulmonary bypass surgery.

Methods: Only those patients who had estimates of the ratio of mean pulmonary arterial pressure to mean systemic arterial pressure and the ratio of arterial blood oxygen tension to fraction of inspired oxygen determined preoperatively were enrolled. Hemodynamic variables were recorded, and blood samples were obtained for oximetric analysis 5 minutes before and 30 minutes after inhalation of nitric oxide began. The concentration of nitric oxide inhaled was maintained at 20 parts per million. The data were analyzed by using Friedman's repeated measures analysis of variance.

Results: Thirteen patients were enrolled in the study. The mean preoperative ratio of mean pulmonary arterial pressure to mean systemic arterial pressure was 0.63 +/- 0.08 (standard error of the mean), and the mean preoperative ratio of arterial blood oxygen tension to fraction of inspired oxygen was 131 +/- 15 mm Hg. No differences between preoperative and postoperative values were detected. Inhalation of nitric oxide decreased the ratio of mean pulmonary arterial pressure to mean systemic arterial from 0.53 +/- 0.07 to 0.39 +/- 0.5 and increased the ratio of arterial blood oxygen tension to fraction of inspired oxygen from 167 +/- 35 mm Hg to 235 +/- 45 mm Hg. Inhalation of nitric oxide also decreased the intrapulmonary shunt fraction from 0.29 +/- 0.05 to 0.19 +/- 0.04.

Conclusions: Inhalation of nitric oxide selectively decreases pulmonary vascular tone and increases ventilation-perfusion matching in patients with persistent pulmonary hypertension and hypoxemia after surgery requiring cardiopulmonary bypass. Inhalation of nitric oxide may be a valuable adjunctive therapy for these patients.