Patients undergoing sedated bronchoscopy were randomized into six groups (10 Liters/minute [L/min], 20 L/min, 30 L/min, 40 L/min, 50 L/min, 60 L/min). The primary outcome was the incidence of hypoxemia.

It's a double-blind, randomized trial. The patients'demographic information, such as sex, weight, height, smoking status, present illness and history of past illness, were collected. After successful peripheral intravenous access, all patients, before sedation, received 20 min nebulization with lidocaine via a nebuliser facemask. The basic oxygen saturation, heart rate, and blood pressure of the patients were recorded by the investigators.Patients in the HFNO group received humidified oxygen at different rates via a high-flow nasal cannula (AIRVO2, New Zealand). After sedation with propofol and sufentanil, continuous electrocardiography and pulse oximetry were recorded, and the blood pressure of the patients was monitored throughout the procedure. . After bronchoscopy, patients were transferred to the post anesthesia care unit (PACU) if their vital signs were stable.

Inclusion Criteria:

• (1) undergoing sedated bronchoscopy
• (2) 18 to 70 years of age;
• (3) American Society of Anaesthesiologists (ASA) class: I-III

Exclusion Criteria:

• (1) severe cardiac disease, including aortic stenosis, mitral stenosis, hemodynamic instability caused by severe arrhythmia, and acute myocardial infarction or cardiac surgery within the last 6 months;
• (2) severe hypoxemia (SpO2 < 90% without oxygen supply on admission), caused by interstitial lung disease, end-stage chronic obstructive pulmonary disease (COPD) or other diseases;
• (3) upper respiratory tract infection or lung infection;
• (4) refusal to participate in this study.