The goal of this clinical trial is to compare three airway intubation devices in adult patients undergoing general anesthesia who require tracheal intubation. The main questions it aims to answer are:

• Does the SPHJ-II video-assisted adjustable red-light fluoroscopic tracheal intubation scope improve first-attempt intubation success compared with a visual lighted stylet and a visual intubation fiberscope?
• How do the three devices compare in intubation efficiency, intubation-related complications, and peri-intubation physiological responses?

Researchers will compare the SPHJ-II, the visual lighted stylet, and the visual intubation fiberscope to evaluate their performance during tracheal intubation.

Participants will be randomly assigned to one of the three device groups and undergo tracheal intubation during general anesthesia using the assigned device.

Tracheal intubation is an essential procedure for airway management during general anesthesia. Several visualized intubation devices are used in clinical practice, but each has different advantages and limitations in visualization, maneuverability, and ease of endotracheal tube placement. The SPHJ-II is a novel video-assisted adjustable red-light fluoroscopic tracheal intubation scope designed to improve visualization and facilitate intubation.

This study is a prospective, randomized, single-center, single-blind, parallel-group clinical trial designed to compare the clinical performance of the SPHJ-II, a visual lighted stylet, and a visual intubation fiberscope in adult patients undergoing general anesthesia requiring tracheal intubation. Participants will be randomly assigned in a 1:1:1 ratio to one of the three device groups. All tracheal intubations will be performed by experienced anesthesiologists using standardized operating procedures. The study is designed to evaluate whether the SPHJ-II provides advantages in first-attempt intubation success and procedural performance compared with the other two commonly used visualized intubation devices.

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.

Individual participant data will not be shared because the study involves patient-level clinical data and no formal data-sharing plan has been established.

Participants are anesthetized during the intervention and are not informed of the assigned intubation device. The anesthesiologist performing tracheal intubation is not blinded because knowledge of the assigned device is necessary for the procedure. Postoperative follow-up personnel and outcome assessors responsible for data collection will remain blinded to treatment allocation whenever feasible.