The following three landmarks for a deep cervical plexus block are
identified and marked (Figure 23–5):
To estimate the line of needle insertion that overlies the transverse
processes, the mastoid process (MP) and Chassaignac's tubercle, which is the
transverse process of the sixth cervical vertebra (C6), are identified and
marked (Figure 23–6). The transverse process of C6 is usually
easily palpated behind the clavicular head of the sternocleidomastoid muscle
at the level just below the cricoid cartilage (Figure 23–7). Next,
a line is drawn connecting the MP to Chassaignac's tubercle. Position the
palpating hand just behind the posterior border of the sternocleidomastoid
muscle. Once this line is drawn, label the insertion sites over the C2, C3,
and C4, which are respectively located on the MP–C6 line 2 cm, 4 cm, and 6
cm caudal to the mastoid process. It is also possible to perform a single
injection at the C3 level, which is considered safe and
effective.32