Objective: To determine the different effect of prone-position ventilation (PPV) in patients with acute respiratory distress syndrome (ARDS) resulting from a pulmonary cause (ARDSp) and that from an extrapulmonary cause (ARDSexp) on oxygenation, respiratory mechanics and hemodynamics. To determine an appropriate duration of ventilation in the prone position in the two groups.
Methods: Nine ARDSp patients and seven ARDSexp patients within 3 days of onset of ARDS were included in this study which were classified as two groups. The patients were placed in prone position for 2 h. The effect of different time (pre-PPV, PPV 0.5 h, PPV 2 h) on oxygenation, respiratory mechanics and hemodynamics were observed. Lung computerized tomography (CT) was obtained in both the supine position and 10 min after prone position.
Results: Compared with pre-PPV, in ARDSp, partial pressure of oxygen in artery (PaO(2))/inhaled oxygen concentration (FiO(2)) was not increased after 0.5 h, and increased only after 2 h in the prone position (130.6 +/- 36.2 to 165.1 +/- 72.3, P < 0.05). But in ARDSexp, PaO(2)/FiO(2) was significantly increased after 0.5 h and 2 h in the prone position (116.5 +/- 55.0 to 163.2 +/- 46.4 and 182.7 +/- 87.7, P < 0.05). After 0.5 h in the prone position the responding ratio of ARDSexp was higher than ARDSp (7/7 vs 1/9, P = 0.0007). After 2 h, no significant difference of responding ratio was found between the two groups (6/7 vs 6/9, P = 0.392). The changes of the PaO(2) were similar to the PaO(2)/FiO(2). The PaCO(2) and the static respiratory system compliance (Cstrs) did not differ significantly between the prone position and the supine position in the two groups. In ARDSp, the airway resistance was (10.8 +/- 1.4) cm H2O.s(-1).L(-1) in the supine position, and it was significantly decreased after 2 h in the prone position (8.4 +/- 1.8) cm H2O.s(-1).L(-1) (P < 0.05). Chest CT scans of ARDSp and ARDSexp patients showed marked difference.
Conclusions: PPV could be used to improve severe hypoxemia of ARDS. It improved the PaO(2)/FiO(2) ratio rapidly in ARDSexp, but in ARDSp the improvement took a longer time.