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.