 During the intervention period of the present study, we intend to assess and monitor the evolution of lung recruitment, as recently suggested and described in detail by Gattinoni and colleagues 13. The recruitment-assessment protocol will be as follows: 1 HFO-TGI-group: CT of the thorax at baseline, and at days 5 and 8 post-randomization; 2 CMV-group: CT of the thorax at baseline, and at day 8 post-randomization. Patients will be considered as eligible for CT-evaluation if PaO2FiO2 is in-between 100-150 mmHg, and if there is no additional concern with respect to patient transportation safety to the CT suite, as confirmed by the attending physicians on a case-by-case basis. The rationale for this investigational intervention comprises the elucidation of the mechanism of the HFO-TGI-induced physiological benefit. 