High-flow Nasal Oxygen Therapy in Obese Patients Undergoing Sedativegastrointestinal Endoscopy

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.

Inclusion Criteria: 1. Patients undergoing sedative gastrointestinal endoscopy 2. Aged over 18. 3. ASA classification I-III 4. BMI\>28kg/m2 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.