EFFECTS OF INHALED NITRIC-OXIDE ON RESPIRATORY SYSTEM MECHANICS, HEMODYNAMICS, AND GAS-EXCHANGE AFTER CARDIAC-SURGERY

Objective: To evaluate the hemodynamic and respiratory effects of inha led nitric oxide (NO) in postoperative cardiac patients. Design: A pro spective evaluation. Setting: A university hospital intensive care uni t. Participants: Fourteen adults with pulmonary hypertension, studied postoperatively. Interventions: 60 minutes of NO inhalation (20 ppm). Measurements and Main Results: Respiratory mechanics were analyzed by inflating the relaxed respiratory system with constant flow, followed by rapid airway occlusion at end-inflation, which was maintained until a plateau in tracheal pressure was obtained. Gas exchange and hemodyn amics were evaluated by conventional means. The data were studied usin g the analysis of variance for repeated measures. Minimum airway resis tance (Rmin) increased significantly from 8.87 +/- 3.24 cm H2O/L.s to 9.69 +/- 3.22 cm H2O/L.s at the end of NO inhalation and remained elev ated after NO was discontinued. A selective vasodilator effect on pulm onary vasculature was observed in the pulmonary-systemic vascular resi stance ratio, which decreased from 0.18 +/- 0.11 to 0.13 +/- 0.08 at t he end of inhalation and returned to baseline values after gas suspens ion. No significant alterations in oxygenation were observed. Conclusi on: The effects of NO as a powerful and useful vasodilator agent were confirmed. However, it is important to be aware that the effects obser ved on respiratory mechanics may interfere with the final response of the respiratory system to NO.