Short-term effect of inhaled nitric oxide and prone positioning on gas exchange in patients with severe acute respiratory distress syndrome

Objective: To compare the short-term effects of inhaled nitric oxide (NO) and prone positioning in improving oxygenation in acute respiratory distress syndrome (ARDS). Methods: Charts of consecutive ARDS patients (lung injury score >2) during a 2-yr period, tested for both inhaled NO and prone positioning efficacy were retrospectively reviewed. Variations in the Pao(2)/Fio(2) ratio induced by inhaled NO and prone positioning were evaluated. Measurements and Main Results: Twenty-seven patients (age, 42 +/- 17 yrs) were included. Simplified Acute Physiology Score II was 45 +/- 14, Mortality rate in the intensive care unit was 63%. The causes of ARDS were pneumonia (n = 14), extra-lung infection (n = 5), and noninfectious systemic inflammatory response syndrome (n = 8), Lung injury score was 2.7 +/- 0.3. At baseline, before the initiation of inhaled NO, the Pao(2)/Fio(2) ratio was 97 +/- 46 torr and before prone positioning, 92 +/- 26 torr, Variations in the Pao(2)/Fio(2) ratio were lower at start of NO therapy (11 +/- 4 ppm) than that observed at prone positioning initiation (23 +/- 31 vs. 62 +/- 78 torr, p < .05). An increase in variations in the Pao(2)/Fio(2) ratio of >15 torr was associated with prone positioning in 16 patients (59%) and with NO inhalation in 13 patients (48%) (not significant). An increase in variations in the Pao(2)/Fio(2) ratio of >15 torr was associated with both techniques in only six patients (22%). There was no correlation between the response to prone positioning and the response to inhaled NO (r(2) = .005; p = .73). Conclusions: Prone positioning improves hypoxemia significantly better than does inhaled NO. The response to one technique is not predictive of the response to the other technique.