 In the HFO-TGI group, recruitment maneuvers will be performed at the onset and at 3 and 5 h following the onset of each HFO-TGI session, and just after to return to CMV. In the CMV-group, 4 recruitment maneuvers one every 4-6 h; starting at 07:00 will be performed daily. In both groups, recruitment maneuvers will be continued for the first 4 days post-randomization 12. 