Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) was revealed to prolong apneic time with a slow increase in carbon dioxide; thus, has been used for preoxygenation in patients with difficult airways or requiring rapid sequence induction in general anesthesia.

However, in patients undergoing hypopharyngeal and laryngo-tracheal surgery, THRIVE during operation can be advantageous by allowing tubeless surgical field with sufficient oxygenation.

Therefore, the investigators conducted this study to evaluate the efficacy of THRIVE on prolonged apneic time with enhanced surgical conditions in patients with laryngeal microsurgery.

Patients undergoing laryngeal microsurgery will be randomized into either intubation group or THRIVE group.

On arriving operating room, the patients will be preoxygenated by facemask or high flow nasal cannula with 100% oxygen for 3 minutes according to the allocated group. After inducing general anesthesia, patients in intubation group will be oxygenated by endotracheal tube, while patients in THRIVE group will be oxygenated by high flow nasal cannula with flow rate of 70L/min. During the surgery, the endotracheal tube can be removed and reintubated in intubation group patients to provide surgical field by a surgeon, respectively.

The monitored pulse oximetry, oxygen reserve index, and transcutaneous partial pressure of carbon dioxide will be recorded during surgery.

Inclusion Criteria:

• patients undergoing laryngeal microsurgery
• ASA class I-III

Exclusion Criteria:

• patients scheduled for laryngeal microsurgery using CO2 laser
• patients with increased intracranial pressure
• patients with skull base defect
• patients with chronic obstructive pulmonary disease
• patients with pulmonary hypertension
• patients requiring rapid sequence induction