Ultrasound-guided cervical selective nerve block at the C4 level. The needle (arrows) is advanced caudally, at an angle of 45-60°, until its tip (asterisk) comes close to the C4 nerve root (yellow circle). The shape of the transverse process is delineated (blue line). The carotid artery (CA) and jugular vein (JV) are located medial to the needle track, whereas the sternocleidomastoid muscle (SCM) is located superficially.