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