Effects of inhaled iloprost on acute respiratory distress syndrome in prone and supine positions

Introduction

In several studies it has been shown that inhaled pulmonary vasodilators (NO and iloprost) can decrease the pulmonary hypertension and also improve the oxygenation during acute respiratory distress syndrome (ARDS) [1]. We investigated the effects of prone and supine positioning on the effects of inhaled iloprost in an animal-ARDS model.

Methods

After approval of the animal ethics committee, 10 pigs were anesthetized and intubated. Invasive systemic and pulmonary arterial catheterizations were performed (T1). ARDS was induced in all animals with the infusion of oleic acid (0.15 to 0.30 ml/kg). The study design is shown in Figure 1. Hemodynamic and respiratory parameters and ventilation parameters were measured; arterial and mixed venous blood samples were drawn; and were recorded in T1 to T6. Pigs were ventilated in volume-controlled ventilation mode with FiO₂ 100%, with 4 cmH₂O positive end-expiratory pressure (PEEP) in the beginning and with 8 cmH₂O PEEP after induction of ARDS. Statistical analysis was made with Student's t test, repeated measures of ANOVA (with Tukey as the post-hoc test) and paired t tests. P < 0.05 was significant.

Figure 1

Ilop, iloporost; Pron, prone; Sup, supine.

Results

There was no significant difference between the sequences. Iloprost decreased the mean pulmonary arterial pressure in both supine (37 vs. 31 mmHg) and prone (38 vs. 29 mmHg) positions significantly, but there was no significant difference between both positions. Prone position was associated with an improvement in oxygenation compared with supine position both with or without iloprost application. There was no spillover effect of iloprost.

Conclusion

Iloprost decreased pulmonary arterial pressures in both positions. On the other hand, the prone position improved oxygenation. The decrease in pulmonary arterial pressures and improvement in oxygenation was better in prone position + iloprost; however, these findings were not statistically significant.