PHYSIOLOGICAL DETERMINANTS OF THE RESPONSE TO INHALED NITRIC-OXIDE INPATIENTS WITH ACUTE RESPIRATORY-DISTRESS SYNDROME

Background: The response to inhaled nitric oxide (NO) in patients with acute respiratory distress syndrome (ARDS) varies. It is unclear whic h patients will respond favorably and whether the initial response per sists over time. The authors defined a clinically useful response to i nhaled NO as an increase of more than 20% of the ratio of the partial pressure of oxygen (Pa-O2) to the inspiratory fraction of oxygen (FiO( 2)), a decrease of more than 20% of pulmonary vascular resistance, or both, The authors hypothesized that patients who initially respond fav orably are likely to show persistent improvements of gas exchange and hemodynamics after 48 h of NO inhalation. Methods: The medical records and collected research data of 88 patients with ARDS who received 92 trials of NC, inhalation between March 1991 and February 1996 were rev iewed. Results: Fifty-three of the 92 trials (58%) produced a clinical ly significant response to NO. In the responding patients who continue d to receive NO therapy (n = 43), the Pa-O2/FiO(2) ratio remained high er (120 +/- 46 vs. 89 +/- 32 mmHg before NO; P < 0.01) and the mean pu lmonary artery pressure remained lower (35 +/- 8 vs. 40 +/- 12 mmHg be fore NO; P < 0.01) at 48 h. Only 33% of the patients with septic shock responded to inhaled NO compared with 64% of those without septic sho ck (P < 0.02). Conclusions: Most patients with ARDS had clinically use ful responses to NO inhalation. Patients with an initial favorable res ponse maintained the improvement at 48 h, Patients with septic shock w ere less likely to respond favorably.