Two Modes of Mechanical Ventilation for Intensive Care Patients With Low Blood Oxygen Due to Breathing Difficulties

Inclusion Criteria: * Admitted to the ICU * Invasive mechanical ventilation with FiO2 ≥ 50% OR PaO2-to-FiO2 ratio \<20 kPa, including PEEP 3 5 cmH20 for at least 6 hours Exclusion Criteria: * Meeting inclusion criteria for more than 24 hours * Severe bronchospasm, defined as warranting treatment aimed at reversing this i.e. inhalation of anticholinergic or bronchodilator beyond what the patient normally use * Emphysema where treating physician judges the patient at increased risk for pneumothorax from APRV * Restrictive lung disease defined as a pre-admission diagnosis of restrictive lung disease * Undrained pneumothorax * Hemodynamic instability defined as more than 0.20 microgram/kg/min of norepinephrine or any dose of adrenaline infusion to maintain MAP ≥ 65 mmHg * Age \< 18 years * Patients who have received APRV previously during the current ICU admission * Patients in prone position within the last 24 hours