Handling Oxygenation Targets in the Intensive Care Unit

Inclusion Criteria: * Acutely admitted to the ICU AND * Aged ≥ 18 years AND * Receives supplemental oxygen with a flow of at least 10 L per minutes in an open system including high-flow systems OR at least a FiO2 of 0.50 in a closed system including invasive or non-invasive ventilation or CPAP systems AND * Expected to receive supplemental oxygen for at least 24 hours in the ICU AND * Having an arterial line for PaO2 monitoring Exclusion Criteria: * Cannot be randomised within twelve hours after present ICU admission * Chronic mechanical ventilation for any reason * Use of home oxygen * Previous treatment with bleomycin * Organ transplant during current hospital admission * Withdrawal from active therapy or brain death deemed imminent * Fertile woman (\< 50 years of age) with positive urine human gonadotropin (hCG) or plasma-hCG * Carbon monoxide poisoning * Cyanide poisoning * Methaemoglobinaemia * Paraquat poisoning * Any condition expected to involve the use of hyperbaric oxygen (HBO) * Sickle cell disease * Consent not obtainable according to national regulations * Previously randomised into the HOT-ICU trial