To determine whether high-flow nasal cannula oxygen can reduce the incidence of hypoxia during the procedure of sedated hysteroscopy.

Inclusion Criteria:

1. 20 years old ≤ age ≤ 50 years old, female.
2. Undergoing hysteroscopy sedated with propofol for diagnosis or treatment.
3. Informed consent
4. BMI≤28kg/m2.
5. ASA physical status Ⅰ~ Ⅱ.

Exclusion Criteria:

1. Epistaxis, nasal congestion and nasal mucosal damage.
2. Confirmed brain disease (cranial trauma, tumor, stroke, cognitive dysfunction etc.).
3. Confirmed severe heart disease (heart failure, angina pectoris, myocardial infarction, arrhythmia, etc.).
4. Confirmed severe lung diseases (upper respiratory tract infection, asthma, bronchitis, COPD, bullae, pulmonary embolism, pulmonary edema, lung cancer, etc.).
5. Pregnant women.
6. Acute and chronic hepatitis or liver cirrhosis with severe abnormal liver function.
7. Acute and chronic nephritis with severe abnormal renal function or renal failure.
8. Needing oxygen inhalation for underlying diseases.
9. Emergency surgery.
10. Combined with multiple trauma.
11. Allergic to soybean