Table 1. Preoxygenation and apneic oxygenation protocol based on the severity of acute respiratory failure.

Severity of the acute respiratory failure	Suggested preoxygenation technique (3–4 minutes if time permits)
Mild (200 mmHg < pO2/FiO2 <300 mmHg)	Face-mask or nasal cannula (standard or HFNO) or bag-mask oxygenation, at the highest possible FiO2
	Maintain nasal cannula in place during laryngoscopy, if used for preoxygenation
	Bag-mask ventilation if SpO2 drops below 90%
Moderate (100 mmHg < pO2/FiO2 <200 mmHg)	Non-invasive ventilation [also including continuous positive airway pressure (CPAP)] with PEEP 5–10 cmH2O and FiO2 100%
	Consider apneic oxygenation with nasal cannula oxygen (standard or HFNO) during intubation
	Bag-mask ventilation with PEEP 5–10 cmH2O if SpO2 drops below 90%
Severe (100 mmHg < pO2/FiO2)	Non-invasive ventilation (also including CPAP) with PEEP 5–10 cmH2O and FiO2 100%
	Consider awake fibreoptic intubation without interrupting non-invasive ventilation, through dedicated masks
	Otherwise, consider apneic oxygenation with nasal cannula oxygen (standard or HFNO) during intubation
	Bag-mask ventilation with PEEP 5–10 cmH2O if SpO2 drops below 90%

HFNO, high-flow nasal oxygen.