To verify the association between respiratory system mechanical properties (ΔP, ΔPL,dyn, Pmus, Pplat and CRS and CL,dyn) assessed during assisted modes of ventilation (as average over the first three days since enrollment) and ICU mortality.

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.

AHRF/ARDS patients on Assisted Mechanical Ventilation modes from international centers will be enrolled. All the pressure-targeted modes of assisted ventilation will be acceptable for the study inclusion.