CMV strategy Eligible study participants will have received at least 60 min of lung protective CMV with the following combinations of FiO2/PEEP: 0.5/10-12 cm H2O, 0.6/14-16 cm H2O, 0.7/14-16 cm H2O, 0.8/14-16 cm H2O, 0.9/16-18 cm H2O, 1.0/20-24 cmH2O. These combinations constitute "general" recommendations and further PEEP titrations of =< 4 cm H2O by attending physicians to the "best" combination of the patients' gas exchange and hemodynamic will be considered as acceptable. A high-PEEP-associated survival benefit has been recently documented. Whenever oxygenation deteriorates, PEEP will be increased first, followed by an increase in FiO2, while targeting "concordance" with the aforementioned FiO2/PEEP combinations.