The aim of this clinical trial is to compare the effectiveness and safety of ultrasound-guided thyroid cartilage plane approach with the superior laryngeal nerve space approach for superior laryngeal nerve block in awake tracheal intubation. Patients were randomized into the thyroid cartilage plane block group (T group) or the superior laryngeal nerve space block group (C group). In Group T, bilateral thyroid cartilage plane block was performed under ultrasound with thyroid cartilage as the landmark, and local anesthetic was injected on the surface of the thyroid cartilage. In Group C, local anesthetic was injected into the space between the thyrohyoid membrane and muscle groups above.

We aim to evaluate whether the thyroid cartilage plane approach is not inferior to the superior laryngeal nerve space approach for ultrasound-guided superior laryngeal nerve block in awake tracheal intubation

After entering the operation room, ECG, SPO2, and invasive blood pressure were monitored. Sedation was facilitated. The proper anaesthesia depth was maintained at 60-80 using the bispectral index. Additionally, 0.5 mg of Penehyclidine Hydrochloride was injected intravenously once the venous access was established. 100% oxygen 4 L min-1 was administered with a nasal cannula throughout the procedure. All patients received topical pharyngeal anesthesia using lidocaine spray. We used a 5-12 MHz linear probeto perform bilateral block. The probe was placed parasagittally to locate the thyroid cartilage and superior laryngeal nerve space. After identification of related structure, we advanced a 22-gauge needle medial to the transducer at the upper half of the thyroid cartilage laminae until it touched the laminae or superior laryngeal nerve space using the out-of-plane technique. The correct location of the needle tip in the fascial deep to the muscle groups was confirmed by injecting 0.5-1 ml saline. A total of 2% lidocaine 2.5 ml was administered after negative aspiration bilaterally. "Spray-as-you-go" technique guided by a fiberoptic bronchoscope was performed to the tracheal with 5 ml of 2% lidocaine. After airway anesthesia, intubation completed.

The primary outcome was the proportion of acceptable intubation conditions (AIC). Secondary outcomes were the performance time, Ramsay sedation score, the patient's cough condition, comfort score, and tracheal tube tolerance score and other perioperative complications including airway hemorrhage and superior laryngeal nerve damage.

Inclusion Criteria:

1. Patients scheduled for awake tracheal intubation under general anesthesia.
2. Patients with difficult airways (e.g., limited cervical spine mobility, full stomach, partial airway obstruction, craniofacial deformities or trauma, micrognathia, mouth opening <3cm, Mallampati III or IV classification) posing challenges for mask ventilation or intubation.
3. Age between 18 and 85 years old.
4. Gender is not restricted.
5. ASA classification of I - III.

Exclusion Criteria:

1. Cardiovascular dysfunction or arterial aneurysms.
2. Mental or neurological disorders or concomitant arterial aneurysms.
3. Infection at the puncture site.
4. Allergy to local anesthetics.
5. Continuous use of antiplatelet or anticoagulant medications preoperatively.
6. Hoarseness or coughing while drinking water.
7. Bronchial asthma.
8. Participation in other clinical trials within the previous 3 months before enrollment 9.r current participation in other clinical trials.