The Effects of High-flow Nasal Oxygen on Oxygenation During Rigid Bronchoscopy Under General Anesthesia in Pediatric Patients

Inclusion Criteria: * 1\. Patients undergoing general anesthesia with stent placement or bougination, biopsy or removal of a foreign body or a mass through a rigid bronchoscope * 2\. Patients aged 7 or younger who meet American Society of Anesthesiologists (ASA) physical class 2-4 Exclusion Criteria: * 1\. Patients undergoing extracorporeal membrane oxygenation (ECMO) * 2\. Patients with active nasal bleeding), severe nasal obstruction, recent nasal trauma of surgery * 3\. Patients with current maxillofacial trauma or basal skull fracture * 4\. Patients with active nasal bleeding), severe nasal obstruction, recent nasal trauma of surgery * 5\. Extremely low birth weight infant and premature infant less than 28 weeks gestation age * 6\. Patients who had previously undergone rigid bronchoscopy / surgery * 7\. If the parent of subject includes a person who can not read the written consent (eg, illiterate, foreigner, etc.)