Obesity is associated with adverse airway events including desaturation during deep sedation. Previous studies have suggested that high-flow nasal oxygenation may be superior to regular (low-flow) nasal cannula for prevention of hypoxia during Sedated Gastrointestinal Endoscopy in non-obesity patients. The prerequisite of high-flow nasal oxygenation is keeping airway patency. Our pervious study demonstrated that nasopharyngeal airway has the similar efficacy of jaw-lift. In present study we aimed to determine whether high-flow nasal oxygenation combined with nasopharyngeal airway could reduce the incidence of hypoxia during Sedated Gastrointestinal Endoscopy in obese patients.

Inclusion Criteria:

1. Patients receiving selective combined upper intestinal and lower intestinal endoscopy procedure under deep sedation.
2. Age ranging from 19 to 80, both male and female
3. Obese patients，BMI ≥ 28kg/m^2
4. ASA I~III
5. Patients should clearly understand and voluntarily participate in the study, with signed informed consent.

Exclusion Criteria:

1. Patients with acute respiratory infection in the last 2 weeks
2. Patients with nasal congestion, epistaxis, recent nasal trauma, recent nasal surgery
3. hypoxia, defined as oxygen saturation measured by pulse oximetry (SpO2) ≤ 95% before preoxygenation.
4. Common advanced gastrointestinal endoscopy procedures meeting eligibility criteria included cholangiopancreatography, endoscopic ultrasound procedures, endoscopic mucosal resection and endoscopic retrograde cholangiopancreatography (ERCP) procedures.
5. coagulation disorders or platelets < 100*10^9/L
6. Have serious heart diseases such as severe arrhythmia, heart failure, Adams Stokes Disease, unstable angina pectoris, myocardial infarction in the last 6 months, history of tachycardia / bradycardia requiring medical treatment, third degree atrioventricular block or QTC interval ≥ 450ms (corrected according to fridericia's formula), or exercise tolerance < 4mets
7. Allergy to eggs, soy products, opioids and other drugs, propofol, etc.
8. Participated in other clinical trials as a subject within 3 months
9. Patients with brain injury, possible convulsion, myoclonus, intracranial hypertension, cerebral aneurysm, cerebrovascular accident history, schizophrenia, intellectual disability, mania, psychosis, long-term use of psychotropic drugs, drug addiction, cognitive dysfunction history, etc.
10. Emergency procedure
11. Pregnant or breast-feeding women
12. Patients having procedures with planned tracheal intubation or laryngeal mask
13. Investigator considers the patients are inappropriate to participate in this trial