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 exploits this pathophysiology by inducing local vasodilation, thereby increasing ventilation-perfusion matching and reducing hypoxemia. Therefore, aerosolized prostaglandin I efficacy may depend upon FRC. Both P /F and compliance of the respiratory system (C) are indirect signifiers of FRC and thus may partly determine the response to aerosolized prostaglandin I.

Methods: We reviewed the records of 208 ARDS subjects who received aerosolized prostaglandin I and had arterial blood gases done before and after the initiation of therapy, without other ventilator manipulations. Subjects were grouped according to baseline P /F (lowest: < 60, intermediate: 60-90, highest: > 90 mm Hg) and C (< 20, 20-29, 30-39, and ≥ 40 mL/cm HO) and by other factors, such as sepsis. Comparisons were analyzed by paired 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. α was set at .05.

Results: Mean P /F increased by 33 mm Hg (42%) upon initiation of prostaglandin I, with a responder rate of 62%. P /F increased significantly in all oxygenation groups. The highest baseline P /F 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 /F compared with those without sepsis (18 ± 35 vs 40 ± 55 mm Hg, = .002). Both P /F and responder rate increased as C 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 were baseline P /F (odds ratio 1.10 [1.004-1.205], = .042) and C (odds ratio 1.04 [1.01-1.08], = .02).

Conclusions: Aerosolized prostaglandin I improves oxygenation in approximately 60% of ARDS cases. A favorable response was most strongly associated with baseline P /F and C.