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 (P(aO2)) 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 P(aO2)/FIO2 ratio with NO, from 74 +/- 30 mmHg (mean +/- SD) to 95 +/- 41 mmHg (P < 0.001). In three patients (14%), P(aO2) 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 P(aO2) in individual patients. The baseline P(aO2)/FIO2 ratio and mixed venous oxygenation (P(vO2)) were significantly lower, and the venous admixture was greater in patients showing beneficial effects of NO inhalation on P(aO2).


CONCLUSIONS
Repeated NO inhalation caused a consistent improvement in P(aO2) in about one half of these patients with severe ARDS; no significant benefit or inconsistent effects on pulmonary gas exchange were noted in the others. These findings could be related to the complexity of the mechanisms regulating the vasomotor changes in this syndrome. Severe baseline hypoxemia may be associated with a more favorable effect of NO on P(aO2).
Treggiari-Venzi
M
M
Department of Anesthesiology, Pharmacology and Surgical Intensive Care, University Hospital of Geneva, Switzerland.
Ricou
B
B
Romand
J A
JA
Suter
P M
PM
D000208:Acute Disease; D000328:Adult; D000368:Aged; D005260:Female; D006439:Hemodynamics; D006801:Humans; D007231:Infant, Newborn; D008168:Lung / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000008:administration & dosage*; D010100:Oxygen / Q000097:blood; D011659:Pulmonary Gas Exchange; D012127:Respiratory Distress Syndrome, Newborn / Q000188:drug therapy*
D009569:Nitric Oxide; D010100:Oxygen