iSLN block under ultrasound exposure
The patient was positioned with the neck extended. An oblique parasagittal scan was performed between the levels of the hyoid and thyroid cartilage. A 6.0—12.0 MHz linear ultrasound probe (GE Logiq e) was placed with compression to identify the thyrohyoid membrane. A 26G needle (TWLB, Kangdelai Medical Appliances Co. China) was inserted via the out-of-plane technique under ultrasound guidance until the needle tip entered the target space, which was close to superior laryngeal artery below thyrohyoid membrane. 4 ml ropivacaine solution (0.375%, 2 ml each side) was used to block bilateral internal branch of the superior laryngeal nerve..