High-Flow Nasal Oxygen for Preoxygenation in Emergency Surgery Patients With Full Stomachs

Patients will undergo HFNC preoxygenation for 3 minutes with a flow rate of 60 L/min of heated and humidified pure oxygen (100% FiO₂, 37°C - Optiflow; Fisher \& Paykel Healthcare, Auckland, New Zealand). To minimize air contamination, large or medium nasal cannulae will be selected based on the patient's nostril size

Patients will undergo preoxygenation for 3 minutes using a face mask (sized appropriately to fit the patient and ensure an airtight seal) connected to an Aisys CS2 ventilation system (General Electric, GE Healthcare, Oy, Finland). In this group, the ventilation system will be set with a fresh gas flow of 10 L/min, FiO₂ = 100%, without inspiratory support or expiratory positive pressure. The face mask (Economy, Intersurgical, Fontenay-sous-Bois, France) will be removed after induction to enable intubation.