Hypoxia is the most common adverse events during sedated gastroscopy. In present study, high-flow nasal cannula oxygenation will be utilized in order to reduce the hypoxia. At the same time the feasibility and safety will be evaluated.

Inclusion Criteria:

• patients undergoing gastroscope
• age over 18 years old
• Signed informed consent form

Exclusion Criteria:

• Coagulation disorders or a tendency of nose bleeding;
• An episode/exacerbation of congestive heart failure (CHF) that requires a change in medication, diet or hospitalization from any cause in the last 6 months;
• Severe aortic stenosis or mitral stenosis;
• Cardiac surgery involving thoracotomy (e.g., coronary artery bypass graft (CABG), valve replacement surgery) in the last 6 months;
• Acute myocardial infarction in the last 6 months;
• Acute arrhythmia (including any tachycardia - or bradycardia) with hemodynamic instability;
• Diagnosed chronic obstructive pulmonary disease or current other acute or chronic lung disease requiring supplemental chronic or intermittent oxygen therapy);
• Increased intracranial pressure;
• ASA >III;
• Mouth, nose, or throat infection;
• Fever, defined as core body temperature > 37.5oC ;
• Pregnancy, breastfeeding or positive pregnancy test
• Emergency procedure