In the control group, patients will receive standard of care anesthesia treatment, consisting of conventional preoxygenation and no active oxygen delivery during the apneic phase of induction. Following extubation, supplemental oxygen will be administered via face mask and subsequently weaned to standard nasal cannula as per routine clinical practice.

In the intervention group, patients will receive high-flow nasal oxygen starting from induction of anesthesia until intubation, and from extubation until discharge from PACU with weaning of high-flow nasal oxygen during their PACU stay.

In the intervention group, high-flow nasal oxygen (HFNO) will be initiated at the start of preoxygenation and maintained throughout the apneic phase of induction until successful tracheal intubation. HFNO will be reinitiated immediately prior to extubation and continued throughout the early postoperative period until discharge from the post-anesthesia care unit (PACU). HFNO can be discontinued earlier in the PACU at the discretion of the nurse treating the patient, or upon patient request. HFNO can further be changed to standard of care (standard oxygen mask or standard nasal cannula) at any time at the discretion of the anesthesia provider or PACU nurse. Flow rates and fraction of inspired oxygen (FiO₂) will follow the study protocol (60 liters per minute at 100% O2 for induction of anesthesia, 60 liters per minute at 70% O2 for extubation until 10 minutes after arrival in the PACU with subsequent weaning over the first hour after PACU arrival).

Incidence of desaturation between induction of anesthesia and discharge from PACU, measured as SpO2 <92%

End expiratory lung volume (EELV), measured as difference between pre-oxygenation to post-induction (5min after intubation) and pre-extubation to post-extubation, and pre-extubation to PACU. EELV will be assessed using electrical impedance tomography.