 In the 37-bed intensive care unit ICU of Evaggelismos hospital and the 10-bed ICU of Larissa hospital, a pressure-and volume-limited ventilatory strategy is routinely employed. Consequently, before randomization, patients will already be ventilated Siemens 300C ventilator; or Galileo Gold, Hamilton Medical with one of the ARDSnet-protocol allowable combinations of FiO2 and PEEP 11. Administered tidal volumes will be 5.5-7.5 mLkg-1 predicted body weight, ventilatory rate e.g., 20-35min-1 will be adjusted so that pHa is kept in-between 7.20-7.45; the inspiratory to expiratory time ratio will be 1:1 to 1:3; and the target plateau inspiratory pressure will be 35 cm H2O. Oxygenation goals will be PaO2 60-80 mm Hg or SpO2 90-95. 