Positive end-expiratory pressure and response to inhaled nitric oxide: Changing nonresponders to responders

Background. Inhaled nitric oxide (INO) has been shown to improve oxygenatio n in two thirds of patients with acute respiratory distress syndrome (ARDS) . Failure to respond to INO is multifactorial. We hypothesized that the add ition of positive end expiratory pressure (PEEP) might modify the response to INO in patients who had previously failed to respond to INO. Methods. Patients with ARDS who failed to respond to INO at 1 ppm (PaO2 inc rease of <20%) were selected. Each patient underwent a PEEP trial using an improvement in static lung compliance as the end point. One hour after the new PEEP level was reached, hemodynamic and blood gas values were obtained. INO was then reinstituted at 1 ppm, and hemodynamic and blood gas variable s were obtained 1 hour later. Results. Six of nine patients demonstrated an increase in PaO2/FIO2 (161 +/ - 27 to 186 +/- 29) with a mean increase in PEEP of 3.7 n H2O. Each patient responding to PEEP further improved PaO2/FIO2 (186 +/- 29 to 223 +/- 36) w ith INO at 1 ppm. The three patients who failed to improve after the PEEP i ncrease also failed to respond to a second trial of INO. There were no chan ger in cardiac output or systemic vascular resistance. Pulmonary artery pre ssures decreased slightly (39 +/- 5 vs 38 +/- 7 vs 35 +/- 9 mm Ng). Pulmona ry vascular resistance decreased significantly after reintroduction of INO (298 +/- 131 vs 320 +/- 122 vs 249 +/- 105 dynes/sec/cm(-5)) in patients wh o responded positively. Conclusions The response of ARDS patients to INO can be improved if optimum alveolar recruitment is achieved by the addition of PEEP. PEEP and INO hav e a synergistic effect on PaO2/FIO2. Patients who fail to respond to INO ma y benefit from an optimum PEEP trial.