Inclusion Criteria:  Acute Hypoxaemic Respiratory Failure (defined as respiratory failure requiring invasive mechanical ventilation with a PaO2/FiO2< 300 mmHg) during the course of ICU stay (including ARDS). Invasive mechanical ventilation in one of these modes: Pressure A/C, PRVC, SIMV PC, PSV, NAVA, PAV+, BiPAP Presence of spontaneous breathing activity (ventilator triggering), since 6 hours and no longer than 48 hours Patient for full active management at this point.  Exclusion Criteria:  Age <18 years old Pregnancy Active air leaks Moribund state High ICP Patient has passed a spontaneous breathing trial (if performed for clinical indication) Known COPD with history of home oxygen therapy and/or non invasive ventilation and/or GOLD III-IV. Non invasive ventilation for sleep apnea is NOT an exclusion criteria.