Hypoxia is the most common adverse event in gastrointestinal endoscopes sedated with propofol. The nasal mask oxygen kit has good sealing to ensure an adequate oxygen supply and is convenient and economical.The aim of this randomized study was to determine whether the nasal mask oxygen kit reduces the incidence of hypoxia in gastrointestinal endoscopes procedures.

Inclusion Criteria:

• 18≤ Age ≤60
• patients undergoing combined gastroendoscopy and colonoscopy procedure
• patients signed informed consent form
• ASA classification I-II
• Estimated procedure time <=45min

Exclusion Criteria:

• Coagulation disorders or a tendency of nose bleeding
• Diagnosed heart disease (heart failure, angina, myocardial infarction, arrhythmia, etc.)
• Diagnosed chronic obstructive pulmonary disease or current other acute or chronic lung disease requiring supplemental chronic or intermittent oxygen therapy)
• hypoxia (SpO2< 90 % )
• Upper respiratory tract infection
• increased intracranial pressure
• Fever (core body temperature >37.5 ℃)
• Pregnancy, breastfeeding, or positive pregnancy test
• Emergency procedure or surgery
• Multiple trauma
• Allergy to propofol or tape and adhesives
• BMI<18.5 or BMI>30

Beginning 3months and ending 5 years following article publication.

The data will be available to other researchers upon request, with information shared after approval by the corresponding author (D-SS).