Inclusion Criteria:  Aged above 18 years old. Requiring elective orotracheal intubation under general anesthesia in the OR. Suspected DI according to airway assessments ，and with low risk of difficult ventilation. Planning to use a Macintosh laryngoscope blade on the first attempt, whether direct or video laryngoscopy. Signed written informed consent. Willingness for the primary anesthesia team to participate.  Exclusion Criteria:  Anterior neck lesions, masses, lacerations, or subcutaneous emphysema. A history of neck operation or tracheotomy. Allergies to ultrasound coupling gel.