The purpose of this study is to determine the efficacy and safety of nasal high flow oxygen therapy during diagnostic bronchoscopy.

Hypoxemia is frequently seen during diagnostic bronchoscopy. Nasal prong or other existing oxygen supply methods are often difficult to maintain adequate oxygenation during bronchoscopy. In particular, bronchoscopy to patients already showing hypoxemia can be dangerous even though applying conventional oxygen therapy. Thus, we want to elucidate the usefulness of nasal high flow oxygen therapy to hypoxemic patients 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)