High-flow Nasal Cannula Oxygenation Decrease Hypoxia in Sedated Gastrointestinal Endoscopes in 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