Obese patients often have fat accumulation in the head and neck, increased soft tissue in the oropharynx, decreased lung compliance, decreased lung volume and residual volume, and some obese patients also suffer from obstructive sleep apnea. Therefore, obese patients may experience hypoxemia during sedative gastroscopy. High-flow nasal cannula oxygen therapy (HFNC) can provide patients with high-flow (20-70 L/min) and adjustable oxygen concentration (21%-100%) through a special nasal prong catheter. It has the function of warming and humidifying the air, relieving pressure on the nasal mucosa, maintaining airway patency and moisture, reducing the risk of nasal bleeding. In addition, HFNC can generate positive airway pressure (3-7 cmH2O), increase end-expiratory volume, help with alveolar recruitment, prevent atelectasis, and reduce shunts. The flow rate of HFNC is positively correlated with the nasopharyngeal pressure. At a flow rate of 50 L/min, the nasopharyngeal pressure can exceed 3 cmH2O. Obese patients are prone to upper airway obstruction under sedation or anesthesia. The use of HFNC at 70 L/min perioperatively can reduce hypoxemia in patients, but discomfort in the nasopharynx may occur at this flow rate. The optimal flow rate for clinical use of HFNC has not been established. Meta-analysis shows that when the oxygen flow rate during painless esophagogastroduodenoscopy is greater than 30 L/min, it can significantly reduce the incidence of hypoxemia in patients. Therefore, for obese patients undergoing painless esophagogastroduodenoscopy, the investigators propose using HFNC at three different flow rates: 30 L/min, 50 L/min, and 70 L/min, to provide guidance on the optimal flow rate for clinical use of HFNC.

Gastroscopy is a common method for screening and diagnosing digestive diseases, with approximately 23 million cases performed in China annually. However, this invasive procedure can cause patients to experience pain, nausea, vomiting, and coughing. With the advancement of comfortable medical technology, more patients are opting for painless gastroscopy, which offers higher comfort and satisfaction levels for patients and facilitates the operation for endoscopists.

During sedative gastroscopy, nasal cannula oxygen therapy is commonly used to maintain oxygen levels, with oxygen flow rates typically ranging from 2-6L/min. The most common complication during the procedure is hypoxia. For obese patients, the risk of hypoxemia is increased due to fat accumulation in the head and neck, increased soft tissue in the oropharynx, decreased lung compliance and volumes, and potential obstructive sleep apnea. Therefore, appropriate oxygen therapy is crucial in preventing complications in obese patients during gastroscopy.

High-flow nasal cannula oxygen therapy (HFNC) is a new ventilation method that provides patients with high-flow oxygen (20-70L/min) through a special nasal cannula, with adjustable oxygen concentration (21%-100%) and warming and humidifying functionalities. HFNC can alleviate mucosal ciliary pressure, maintain airway patency and moisture, reduce the risk of nasal bleeding, and generate positive airway pressure, aiding in alveolar recruitment and preventing atelectasis.

Studies have shown that HFNC can reduce the occurrence of hypoxia during painless gastroscopy compared to standard oxygen therapy. The positive airway pressure provided by HFNC is crucial in reducing upper airway obstruction and improving ventilation. The optimal flow rate for HFNC in obese patients undergoing gastroscopy remains unclear, but starting at 30L/min has shown benefits in reducing the risk of hypoxemia without significant discomfort.

Therefore, the investigators propose to investigate the effects of HFNC at flow rates of 30L/min, 50L/min, and 70L/min during painless gastroscopy in obese patients to determine the optimal flow rate that minimizes the risk of hypoxemia without causing discomfort.

Inclusion Criteria:

1. Patients undergoing sedative gastroscopy
2. Aged over 18.
3. ASA classification I-III
4. Interincisal distance >6.5cm, no micrognathia, limited mouth opening and limited cervical spine movement
5. Compliance with ethics, patient willing to participate in the trial, signed informed consent form

Exclusion Criteria:

1. Contraindications for endoscopic procedures or patients refusing sedation/anesthesia.
2. Patients with allergies to propofol, eggs, soybeans, or milk.
3. Patients with gastrointestinal obstruction and gastric emptying disorders.
4. Patients with acute pharyngitis, tonsillitis, and upper respiratory tract infections.

5: Patients with acute exacerbations of respiratory diseases such as asthma, bronchitis, and COPD. 6. Patients with acute arrhythmias and severe heart disease (congenital, valvular disease). 7. Patients requiring replacement therapy for severe liver or kidney dysfunction.

8. Patients with severe mental illnesses requiring medication to control symptoms.

9. Patients with moderate to severe anemia, coagulation disorders, and hematological diseases. 10. Patients with severe nasal congestion caused by nasal cavity lesions. 11. Pregnant and lactating patients.