Objectives: To compare the effects of 5 and 20 ppm of nitric oxide, evaluating time until response for each dose, in patients with adult respiratory distress syndrome (ARDS).
Patients and methods: The study was prospective, controlled and random. Fifteen patients assigned to two groups received either 5 ppm (8 patients) or 20 ppm (7 patients) from November 96 to July 97. The main variables analyzed were PaO2/FiO2 and pulmonary vascular resistance index. We also studied etiology, severity of pulmonary damage as reflected by the Lung Injury Score, age, sex, Apache II prognostic score and exitus. Outcome was considered good if PaO2/FiO2 increased and/or pulmonary vascular resistance index decreased by more than 30% from the initial level (before inhalation of nitric oxide).
Results: The mean lung injury score was 2.9 +/- 0.4 and the two groups were homogeneous. Time until response to nitric oxide was significantly less in the 20 ppm group. Both PaO2/FiO2 and pulmonary vascular resistance index improved significantly in both groups whereas Qs/Qt improved only in the 20 ppm group. We also found that cardiac index and oxygen transport increased, the latter significantly only in the 20 ppm group. NO2 formation was less than 2 ppm and methemoglobin levels did not rise above 2%.
Conclusions: Inhaled nitric oxide significantly improves oxygenation and decreases pulmonary vascular resistance without altering systemic vascular resistance during treatment of ARDS. The final outcomes were similar for both doses, but the 20 ppm dose produced a significantly faster response as well as a significant decrease in Qs/Qt.