Physiologic Determinants of the Response to Inhaled Nitric Oxide in Patients with Acute Respiratory Distress Syndrome

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Abstract
Background: The response to inhaled nitric oxide (NO) in patients with acute respiratory distress syndrome (ARDS) varies. It is unclear which patients will respond favorably and whether the initial response persists over time. The authors defined a clinically useful response to inhaled 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 (FIO2), a decrease of more than 20% of pulmonary vascular resistance, or both. The authors hypothesized that patients who initially respond favorably 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 NO inhalation between March 1991 and February 1996 were reviewed. Results: Fifty-three of the 92 trials (58%) produced a clinically significant response to NO. In the responding patients who continued to receive NO therapy (n = 43), the Pa(O2)/FiO2 ratio remained higher (120 +/- 46 vs. 89 +/- 32 mmHg before NO; P < 0.01) and the mean pulmonary artery pressure remained lower (35 +/- 8 vs. 40 +/- 12 mmHg before 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 shock (P < 0.02). Conclusions: Most patients with ARDS had clinically useful responses to NO inhalation. Patients with an initial favorable response maintained the improvement at 48 h. Patients with septic shock were less likely to respond favorably.