Clinical Research Directory

Inclusion Criteria: * Age 18 to 65 years, inclusive. American Society of Anesthesiologists (ASA) physical status I to III. Scheduled for surgery under general anesthesia requiring endotracheal intubation. The participant or legally authorized representative is fully informed of the purpose, methods, potential risks, and possible benefits of the study and provides written informed consent. Exclusion Criteria: * Anticipated severe difficulty with mask ventilation, such as severe obesity (BMI \> 35 kg/m²) with obstructive sleep apnea syndrome, history of neck radiotherapy, craniofacial malformation, or other conditions judged by the attending anesthesiologist to confer high risk for mask ventilation, and patients requiring awake tracheal intubation. Cervical spine instability, cervical trauma, rheumatoid arthritis involving the cervical spine, ankylosing spondylitis, or any condition requiring absolute cervical immobilization during the procedure. Significant airway involvement identified preoperatively, including imaging evidence of tracheal narrowing with minimal diameter \< 5 mm, severe tracheal compression, displacement or collapse, stridor at rest or after activity, vocal cord paralysis with dyspnea, giant thyroid mass with orthopnea, or other oral, pharyngeal, or laryngeal tumor, edema, stenosis, abscess, or severe upper airway anatomical abnormality affecting glottic exposure or endotracheal tube passage. High risk of reflux and aspiration. Severe cardiovascular disease, severe respiratory disease, severe hepatic or renal dysfunction, severe coagulation disorder, frailty, pregnancy or breastfeeding, or known allergy. Any other condition making the patient unsuitable for participation in the study, such as psychiatric illness, communication disorder, or poor compliance.