Effect of Different-Flow High-Flow Nasal Cannula Versus Traditional Face Mask Oxygenation on Safe Apnea Time in Obese Patients

Obesity is a growing global health problem, and patients with obesity are at higher risk of hypoxemia during induction of general anesthesia. This is because excess body weight reduces the lungs' oxygen storage capacity, causing blood oxygen saturation to decline faster than in normal-weight individuals once breathing stops. Currently, the most common preventive method is preoxygenation with a face mask delivering 100% oxygen for several minutes before anesthesia induction. However, face masks often fail to seal properly in obese patients, potentially compromising preoxygenation effectiveness. High-flow nasal oxygen therapy is a newer technique that delivers heated and humidified oxygen at high flow rates through nasal cannulae. It not only provides effective preoxygenation but may also continue to supply oxygen during apnea (apneic oxygenation), thereby prolonging the safe apnea time. Nevertheless, it remains unclear which flow rate is most effective and whether high-flow nasal oxygen is truly superior to conventional face masks. This prospective randomized controlled trial will enroll 147 obese patients (BMI ≥ 28kg/m²) scheduled for elective surgery at Lianyungang First People's Hospital. Participants will be randomly assigned to one of three groups: (1) traditional face mask preoxygenation at 15 L/min, (2) high-flow nasal oxygen at 45 L/min, or (3) high-flow nasal oxygen at 70 L/min. All patients will receive 100% oxygen for 3 minutes. The primary outcome is safe apnea time - the duration from cessation of breathing until SpO₂ drops to 93%. Secondary outcomes include arterial blood gas values, patient comfort during preoxygenation, tolerance rate, and hemodynamic stability. The study hypothesis is that high-flow nasal oxygen at 70 L/min will provide a longer safe apnea time than both traditional face mask preoxygenation and high-flow nasal oxygen at 45 L/min in obese patients. The results will provide high-quality evidence for optimizing perioperative preoxygenation strategies in this population.