THE RESPONSE TO VARYING CONCENTRATIONS OF INHALED NITRIC-OXIDE IN PATIENTS WITH ACUTE RESPIRATORY-DISTRESS SYNDROME

We investigated the response to varying concentrations of inhaled nitr ic oxide (NO) in 18 patients with acute respiratory distress syndrome (ARDS). The study was divided into two parts. In Part 1, 5-40 ppm of i nhaled NO was evaluated in 10 patients with ARDS. In Part 2, 0.1-10 pp m of inhaled NO was evaluated in eight patients with ARDS. Inhaled NO significantly (P < 0.05) decreased the mean pulmonary artery pressure (MPAP) and pulmonary vascular resistance index (PVRI), and increased t he arterial oxygenation (PaO2) at concentrations of 0.1 to 40 ppm. No dose response was detectable for the pulmonary artery pressure (PAP) o r PVRI over this dose range. The increase in PaO2 at 10 ppm of NO was significantly greater than that at 0.1 ppm but not 1 ppm. The decrease in PVRI and the increase in PaO2 were both significantly correlated w ith the baseline PVRI. While the maximum hemodynamic and oxygenation r esponses to inhaled NO are achieved at approximately 1 ppm, it appears that the maximum hemodynamic response is observed at lower concentrat ions (0.1 ppm) of inhaled NO than the improvement in oxygenation (1-10 ppm). Higher concentrations of NO do not produce any further change i n these variables. It appears that the baseline PVRI may be the best m arker predicting a beneficial response to NO.