The goal of this interventional crossover study, in intubated and mechanically ventilated Acute Respiratory Distress Syndrome (ARDS) patients, is to compare two positive end-expiratory pressure (PEEP) titration techniques regarding: respiratory mechanics, gas exchange, changes in aeration and distribution of ventilation and its impact on cardiac function , specially the right heart (RH). The PEEP titration techniques are : incremental PEEP titration(PEEPinc) and Lung recruitment maneuver plus incremental (LRM plus PEEPdec).