Inhaled nitrous oxide (NO) for the treatment of ARDS

To investigate the initial longterm effect of inhaled NO on hypoxemia in ARDS patients.Retrospective study.Nine hypoxemic patients with ARDS (Murray Lung Injury Score, LIS, 2.8 +/- 0.3), treated with conventional mechanical ventilation.Continuous NO inhalation was started after a test of inhaled NO efficacy on gas exchange and hemodynamics. Long term effects of inhaled NO were evaluated daily in terms of arterial oxygenation and methemoglobin formation.The initial NO inhalation increased the PaO2/FiO2 from 141 +/- 64 mmHg to 216 +/- 70 mmHg (p < 0.0001) and decreased the mean pulmonary pressure from 38 +/- 7 mmHg to 32 +/- 5 mmHg (p < 0.01), the pulmonary venous admixture from 29 +/- 10\% to 20 +/- 8\% (p < 0.01) and the pulmonary vascular resistance from 325 +/- 97 dyne.s.cm-5 to 238 +/- 48 dyne.s.cm-5 (p < 0.01). Daily withdrawal of inhaled NO, which was administered for 14 +/- 16 days at 8 +/- 2 ppm, was associated with a decrease in PaO2/FiO2 by 61 +/- 32 mmHg (p < 0.0001). During prolonged NO inhalation the FiO2 was decreased, on average, by 0.34 +/- 0.19 (p < 0.01), the positive end-expiratory pressure by 4 +/- 2 cmH2O (p < 0.01) and the peak inspiratory pressure by 7 +/- 4 cmH2O (p < 0.01). Three patients died during the ICU stay.Our results confirm the interest for inhaled NO as an additional approach for the treatment of hypoxemia in ARDS. Inhaled NO seems to allow for a better control of gas exchange, rather than for a rapid reduction of the ventilatory support.