Cranial to C4, the cervical plexus is located within the prevertebral layer of deep cervical fascia in a groove between the longus capitis and the middle scalene muscle. At the level of C4- C5, the plexus is located superficial to the prevertebral fascia overlying the interscalene groove, immediately deep to the sternocleidomastoid muscle (SCM).
Deep injection technique: Local anesthetic can be deposited at the C2-C4 paravertebral space, deep to the prevertebral fascia; this blocks the entire plexus (high risk for complications).
Intermediate injection technique: Local anesthetic is injected at the level of the transverse process of C4, between the prevertebral fascia and the investing layer of the deep cervical fascia.
Superficial injection technique: At the level of C6, the local anesthetic is injected subcutaneously and superficially to the deep cervical fascia to block all or specific cutaneous branches.