- more than 48 hours of admission to the emergency department, high dependency or intensive care unit - more than 4 hours on niv or hfnc before enrolment - impending cardiopulmonary arrest - need for immediate endotracheal intubation - hemodynamic instability or life-threatening arrhythmias - gcs < 8 - active intracranial pathology or high icp - inability to cooperate or protect the airway - pregnancy - tracheostomy - dnr or refusing intubation - known type 2 respiratory failure - on chronic home oxygen therapy

- more than 48 hours of admission to the emergency department, high dependency or intensive care unit - more than 4 hours on niv or hfnc before enrolment - impending cardiopulmonary arrest - need for immediate endotracheal intubation - hemodynamic instability or life-threatening arrhythmias - gcs < 8 - active intracranial pathology or high icp - inability to cooperate or protect the airway - pregnancy - tracheostomy - dnr or refusing intubation - known type 2 respiratory failure - on chronic home oxygen therapy

- more than 48 hours of admission - impending cardiopulmonary arrest - need for immediate endotracheal intubation - hemodynamic instability or life-threatening arrhythmias - gcs < 8 - active intracranial pathology or high icp - inability to cooperate or protect the airway - pregnancy - tracheostomy - dnr or refusing intubation - known type 2 respiratory failure - on chronic home oxygen therapy

- more than 48 hours of admission - impending cardiopulmonary arrest - need for immediate endotracheal intubation - hemodynamic instability or life-threatening arrhythmias - gcs < 8 - active intracranial pathology or high icp - inability to cooperate or protect the airway - pregnancy - tracheostomy - dnr or refusing intubation - known type 2 respiratory failure - on chronic home oxygen therapy