In this study, patients undergoing painless gastroscopy were selected to change the nasal catheter oxygen delivery mode to oral oxygen delivery after endoscope implantation, in order to explore the effect of this oxygen delivery mode on the incidence of hypoxemia during general anesthesia gastroscopy.

This study was a randomized controlled study in which patients undergoing elective painless gastroscopy were selected and grouped by random number table. The control group used conventional nasal cannula oxygen method: nasal cannula was used before, during and after gastroscopy was implanted and after withdrawing from the gastroscopy. Test group: Before the gastroscope enters the oral cavity, oxygen is administered through a nasal catheter via the nose. After the gastroscope enters the oral cavity, oxygen is administered through the nasal catheter via the mouth. After the gastroscope is withdrawn, oxygen is administered through the nasal catheter via the nose. The incidence of intraoperative hypoxemia was observed.

Inclusion Criteria:

Patients who receiving gastroscopy under general anesthesia, accompanied with one of the following risk factors of hypoxia:

1. Patients combined with heart or respiratory diseases
2. Age older than 60
3. ASA grading II-III
4. BMI≥30kg/m²,
5. Snoring or having sleep apnea syndrome
6. Patients with a STOP-Bang score ≥ 3 (the risk of OSAS is high) are considered to be highly risk of hypoxia.

Exclusion Criteria:

1. Severe cardiovascular, pulmonary, liver, or kidney disease
2. Patients with infections or tumors of airway
3. History of difficult intubation under general anesthesia
4. Severe sleep apnea syndrome [hypopnea/apnea hypopnea index (AHI)>40]
5. Patients allergic to propofol, eggs, soy or egg whites
6. Pregnancy