The sternal notch, sternal and clavicular heads of sternocleidomastoid muscle, and clavicle are identified and marked. The groove between the anterior and middle scalene muscles is palpated. For ultrasound-guided block, the ultrasound probe is placed as shown by the rectangle in this graphic. For either ultrasound-guided block or nerve stimulator-guided block, the needle insertion site is approximated by the red dot. See the text for description of block technique.