High Flow Nasal OXygen Therapy in High Risk Patients of Hypoxia Undergoing Diagnostic BRONCHOscopy

Inclusion Criteria: 1 or 2 1. PaO2 \< 60 mmHg on ABGA or SpO2 \< 90 % in room air AND SpO2 ≥ 95% or PaO2 ≥ 75mmHg in low flow oxygen therapy 2. Planning to diagnostic bronchoscopic procedure (e.g. bronchial washing, BAL, bronchoscopic biopsy, EBUS-TBNA etc.) Exclusion Criteria: 1. patients who did not agree to provide information 2. patients requiring for emergent intubation 3. patients can not wear or be already applied high flow nasal oxygen therapy 4. patients with unstable vital sign(e.g. severe hypotension, uncontrolled arrhythmia, etc.) 5. patients with multiple organ failures 6. patients with plan to therapeutic bronchoscopic procedure(e.g. intervention)