Study objective: To investigate the initial and long-term effect of nitric oxide (NO) inhalation in patients with severe acute respiratory distress syndrome (ARDS).
Design: Retrospective, clinical study.
Setting: University surgical ICU.
Patients: Eighty-seven patients with severe ARDS.
Interventions and measurements: Thirty of 87 patients with ARDS inhaled low concentrations of NO for more than 48 h in addition to the standard treatment. Initial and long-term effects of NO inhalation on hemodynamics, gas exchange, and methemoglobin formation were determined. Survival of patients treated with inhaled NO was compared with survival in similar patients without NO inhalation.
Results: In 83% of the patients, NO increased the ratio of arterial PO2 to the fraction of inspired O2 (PaO2/FIO2) by > or = 10 mm Hg; in 87%, NO reduced venous admixture (QVA/QT) by > or = 10%, and in 63%, NO decreased mean pulmonary artery pressure (PAP) by > or = 3 mm Hg. Daily short interruption of continuous inhalation of NO for a duration of 17 +/- 2.4 days was consistently associated with a decrease in PaO2/FIO2 by 81 +/- 4 mm Hg (p < 0.001). QVA/QT increased by 8.3 +/- 0.4% (p < 0.001) and PAP by 5.3 +/- 0.3 mm Hg (p < 0.001). Over time, we observed neither tachyphylaxis nor a more pronounced effect of inhaled NO. Methemoglobin increased from 0.74 +/- 0.56% to 0.98 +/- 0.02% (p < 0.001). Survival rates in patients treated with NO did not differ from survival rates in patients not treated with NO.
Conclusion: Beneficial effects of NO inhalation can be observed in most patients with severe ARDS; in some cases, however, it may fail to improve pulmonary gas exchange or to reduce pulmonary hypertension without obvious explanation. To demonstrate a possible increase in survival associated with NO inhalation, large randomized prospective trials are required.