Severity of Hypoxemia and Other Factors That Influence the Response to Aerosolized Prostacyclin in ARDS

BACKGROUND: ARDS is characterized by decreased functional residual capacity (FRC), heterogeneous lung injury, and severe hypoxemia. Tidal ventilation is preferentially distributed to ventilated alveoli. Aerosolized prostaglandin I 2 exploits this pathophysiology by inducing local vasodilation, thereby increasing ventilation-perfusion matching and reducing hypoxemia. Therefore, aerosolized prostaglandin I 2 efficacy may depend upon FRC. Both P aO 2 /F IO 2 and compliance of the respiratory system (C RS ) are indirect signifiers of FRC and thus may partly determine the response to aerosolized prostaglandin I 2 . METHODS: We reviewed the records of 208 ARDS subjects who received aerosolized prostaglandin I 2 and had arterial blood gases done before and after the initiation of therapy, without other ventilator manipulations. Subjects were grouped according to baseline P aO 2 /F IO 2 (lowest: 90 mm Hg) and C RS (< 20, 20–29, 30–39, and ≥ 40 mL/cm H 2 O) and by other factors, such as sepsis. Comparisons were analyzed by paired t tests, or Kruskal-Wallis and Dunn post-tests. Multivariate logistic regression modeling was done to determine which of 18 clinically relevant factors were most predictive for responding to aerosolized prostaglandin I 2 . α was set at .05. RESULTS: Mean P aO 2 /F IO 2 increased by 33 mm Hg (42%) upon initiation of prostaglandin I 2 , with a responder rate of 62%. P aO 2 /F IO 2 increased significantly in all oxygenation groups. The highest baseline P aO 2 /F IO 2 group had the greatest improvement and responder rate (51 ± 63 mm Hg, and 82%). In addition, those with sepsis had a smaller improvement in P aO 2 /F IO 2 compared with those without sepsis (18 ± 35 vs 40 ± 55 mm Hg, P = .002). Both P aO 2 /F IO 2 and responder rate increased as C RS improved, but between-group improvements were not as consistent. In the final model, the only factors that predicted a positive response to aerosolized prostaglandin I 2 were baseline P aO 2 /F IO 2 (odds ratio 1.10 1.004–1.205, P = .042) and C RS (odds ratio 1.04 1.01–1.08, P = .02). CONCLUSIONS: Aerosolized prostaglandin I 2 improves oxygenation in approximately 60% of ARDS cases. A favorable response was most strongly associated with baseline P aO 2 /F IO 2 and C RS .