Hypoxia is the most common adverse event during gastrointestinal endoscopes sedated with propofol and sufentanil, especially in obese people. In the present study, high-flow nasal cannula oxygenation will be utilized in order to reduce the incidence of hypoxia among obesity.

Inclusion Criteria:

• patients undergoing gastrointestinal endoscopes
• age≥18 years old and ≤70 years old
• patients or family members signed informed consent form
• ASA classification I-II
• BMI≥ 28kg/m²

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 the fluid of hemodynamics 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 classification Ⅲ-Ⅳ ;
• Mouth, nose, or throat infection;
• Liver and kidney disease
• Fever, defined as core body temperature > 37.5℃;
• Pregnancy, breastfeeding or positive pregnancy test;
• Emergency procedure;
• Patients or family members refused to participate
• Mental disorders and people without civil capacity