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.
Age 18 to 65 years
American Society of Anesthesiologists (ASA) physical status I ~ III
Scheduled for elective surgery under general anesthesia with endotracheal intubation
Body mass index (BMI) ≥ 28 kg/m²
Cardiac disease including ischemic heart disease, heart failure (New York Heart Association class ≥ 2), current arrhythmia, or pulmonary hypertension
Severe asthma or moderate to severe chronic obstructive pulmonary disease
Pregnancy
Current smoker or former smoker who quit less than 1 year prior to enrollment
Parallel
Face Mask
DeviceFace mask preoxygenation delivered via a tight-fitting mask (appropriate size selected based on facial dimensions) with oxygen flow at 15 L/min, FiO₂ = 1.0 (100% oxygen), for 3 minutes during tidal breathing.
High-Flow Nasal Cannula
DeviceHigh-flow nasal oxygen delivered via a dedicated nasal cannula (size selected based on nostril size), with FiO₂ = 1.0 (100% oxygen), gas heated and humidified (37°C, 100% relative humidity), for 3 minutes with mouth closed and nasal breathing. Flow rates are 45 L/min for the HF45 group and 70 L/min for the HF70 group.
Safe Apnea Time
Safe apnea time is defined as the duration from the onset of apnea (cessation of ventilation after complete neuromuscular blockade following rocuronium administration) to the first decline of peripheral oxygen saturation (SpO₂) to 93%, measured in seconds. Apnea is confirmed by visual assessment by a study team member. Oxygen delivery is discontinued upon confirmation of apnea. The patient remains apneic with the endotracheal tube open to atmosphere until the SpO₂ threshold is reached, at which point mechanical ventilation is initiated and the apnea period is terminated.
Arterial Blood Gas Measurements During Preoxygenation and Apnea
Arterial blood gases are measured at the following time points: (1) at baseline (before preoxygenation), (2) during preoxygenation (at 1 minute and 2 minutes and 3 minutes), (3) immediately at the onset of apnea, (4) during apnea (at 1-minute intervals), and (5) immediately at termination of apnea when SpO₂ reaches 93%. Parameters measured include PaO₂, PaCO₂, pH, and other standard blood gas variables.
Preoxygenation Comfort Visual Analog Scale Score
Patient comfort during the 3-minute preoxygenation period is assessed using a visual analog scale (VAS) ranging from 0 to 10, where 0 represents no discomfort and 10 represents extreme discomfort. Patients are asked to indicate their score using a finger marker at approximately 2.5 minutes after the start of preoxygenation.
Preoxygenation Tolerance Rate
Preoxygenation tolerance rate is defined as the proportion of patients who complete the full 3-minute preoxygenation period without refusal or requiring adjustment of the intervention. Patients who discontinue or request modification of the preoxygenation method during the 3-minute period are recorded as intolerance events.
Systolic blood pressure (SBP)
Systolic blood pressure measured by invasive radial artery monitoring at three time points: (1) baseline before anesthesia induction; (2) immediately after induction (after loss of consciousness following propofol and sufentanil); and (3) immediately after endotracheal intubation.
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