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

PURPOSE: To clarify whether the gas exchange response to prone position is associated with lung recruitability in mechanically ventilated patients with acute respiratory failure. METHODS: In 32 patients, gas exchange response to prone position was investigated as a function of lung recruitability, measured by computed tomography in supine position. RESULTS: 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. CONCLUSIONS: 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.