Relationship between gas exchange response to prone position and lung recruitability during acute respiratory failure

To clarify whether the gas exchange response to prone position is associated with lung recruitability in mechanically ventilated patients with acute respiratory failure.In 32 patients, gas exchange response to prone position was investigated as a function of lung recruitability, measured by computed tomography in supine position.No relationship was found between increased oxygenation in prone position and lung recruitability. In contrast, the decrease of PaCO(2) was related with lung recruitability (R(2) 0.19; P = 0.01). Patients who decreased their PaCO(2) more than the median value (-0.9 mmHg) had a greater lung recruitability (19 +/- 16 vs. 8 +/- 6%; P = 0.02), higher baseline PaCO(2) (48 +/- 8 vs. 41 +/- 11 mmHg; P = 0.07), heavier lungs (1,968 +/- 829 vs. 1,521 +/- 342 g; P = 0.06) and more non-aerated tissue (1,009 +/- 704 vs. 536 +/- 188 g; P = 0.02) than those who did not.During prone position, changes in PaCO(2), but not in oxygenation, are associated with lung recruitability which, in turn, is associated with the severity of lung injury.