The Response to Repeated Nitric Oxide Inhalation Is Inconsistent in Patients with Acute Respiratory Distress Syndrome

Background: Nitric oxide (NO) is administered frequently in patients with acute respiratory distress syndrome (ARDS) and pulmonary hypertension. The efficacy of this therapy over several days is not well known. The authors first determined the consistency of the response to repeated administration of NO and then the baseline variables that were associated with improvement in patients with severe ARDS.

Methods: In a prospective trial, 32 mechanically ventilated patients with severe ARDS received 10 parts per million NO by inhalation. In 22 of these patients, its effect was tested repeatedly (up to four times) in several days. Improvement was defined as an increase > 10% in the ratio of pressure of oxygen in arterial blood (PaO sub 2) to the inspiratory pressure of oxygen (FIO2) from baseline. Patients showing such an improvement were maintained on NO inhalation.

Results: Twelve of the 22 patients (54%) showed a clinically significant and reproducible increase in the PaO2 /FIO2 ratio with NO, from 74 +/- 30 mmHg (mean +/- SD) to 95 +/- 41 mmHg (P <0.001). In three patients (14%), PaO2 did not improve, even with multiple exposures. In seven patients (32%), an inconsistent response was seen on different days. Mean pulmonary artery pressure decreased for the entire group from 34 +/- 10 mmHg to 29 +/- 9 mmHg (P < 0.01), but this decrease did not correlate with the increase in PaO2 in individual patients. The baseline PaO2 /FIO2 ratio and mixed venous oxygenation (PvO2) were significantly lower, and the venous admixture was greater in patients showing beneficial effects of NO inhalation on PaO2.