Exploring the 90% Effective Ventilation Pressure (EP90) for Esophageal Insufflation Avoidance During Anesthesia Induction: The aim is to determine the optimal ventilation pressure for esophageal insufflation avoidance during anesthesia induction and to explore its guiding significance for anesthesia management. The goal is to provide a more precise and personalized ventilation pressure setting standard for clinical anesthesia, thereby enhancing the safety of the anesthesia induction phase.

Pulmonary aspiration of gastric contents has been identified as one of the leading causes of anesthesia-related mortality. Even in fasting patients or those without known aspiration risks, such complications can still occur. In fact, in patients with unprotected airways during apnea, the introduction of air into the lungs during ventilation may become a potential trigger for gastric content aspiration. The entry of air can increase gastric pressure, leading to the reflux of gastric contents into the esophagus, which may subsequently result in hemodynamic instability and pulmonary failure. Therefore, airway management during anesthesia induction is crucial, particularly in the precise control of ventilation pressure, as it directly impacts the safety of the patient during surgery.

Previous studies have used gastric insufflation as the primary endpoint for evaluating the safety of ventilation pressures, often assessing the appearance of gastric gas in the stomach during mask ventilation. However, gastric insufflation typically occurs only after gas has passed through the esophagus and cardia, entering the gastric cavity-this process is a "terminal event" triggered by higher pressures. The esophagus, being structurally weaker than the stomach, is less tolerant to pressure. When gas first enters the esophagus, the cardia is not fully open, and if ventilation pressure continues to rise, it is easy to cause esophageal insufflation, further leading to gastric insufflation and even gastric content reflux. Since esophageal insufflation occurs earlier and has a lower pressure threshold, it can serve as a more sensitive indicator, providing an early warning to anesthesiologists about potential airway management issues.

To address this issue, determining the optimal ventilation pressure to avoid esophageal insufflation is particularly important. the 90% effective ventilation pressure (EP90) refers to the ventilation pressure that can avoid esophageal insufflation in 90% of cases, providing anesthesiologists with a quantitative reference for ventilation pressures.

This study employed a Sequential Allocation with Biased Coin Design (SABCD) trial, utilizing precise statistical methods to explore the EP90 for avoiding esophageal insufflation during anesthesia induction. The goal was to determine the optimal ventilation pressure for preventing esophageal insufflation during anesthesia induction and to explore its implications for anesthesia management. The ultimate aim is to provide a more precise and personalized ventilation pressure setting standard for clinical anesthesia, thereby enhancing the safety of the anesthesia induction phase.

Inclusion Criteria:

1. Age: 18-65 years, regardless of gender;
2. ASA classification: I-III;
3. Scheduled for elective general anesthesia surgery;
4. BMI: 18.0-28.0 kg/m²;
5. Preoperative fasting: Solid food >6 hours, liquid >2 hours;
6. Less than two from five criteria predicting difficult mask ventilation as described by Langeron et al.(Prediction of difficult mask ventilation. Anesthesiology 2000; 92:1229-36);
7. No severe underlying conditions such as heart, lung, liver, or kidney disease;
8. Signed informed consent and ability to cooperate with the study protocol.

Exclusion Criteria:

1. Pregnant or breastfeeding women;
2. History of upper gastrointestinal diseases such as gastroesophageal reflux disease, peptic ulcers, or hiatal hernia;
3. Recent (within 2 weeks) respiratory infections, chronic cough, similar symptoms, and other known or predictable respiratory system diseases;
4. Need for emergency surgery or airway obstruction after anesthesia induction requiring urgent intubation;
5. Inability to achieve adequate oxygenation during mask ventilation (e.g., SpO₂ < 92% for 30 seconds, unresponsive to treatment);
6. History of contraindications or allergies to study medications;
7. Inability to understand the study content or refusal to cooperate;
8. Oropharyngeal or facial pathology;
9. with an indwelling gastric tube, and who had previously undergone gastric surgery.