High-flow Nasal Cannula Oxygenation Decrease Hypoxia in Gastroscopy Sedated by Propofol

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