Indications: Anesthesia and analgesia for carotid endarterectomy, superficial neck, and analgesia for clavicle fractures

Goal: Local anesthetic spread around the superficial branches of the cervical plexus

Transducer: Linear

Needle: 25-22 gauge, 5 cm short bevel

Local anesthetic volume: 5-8 mL

The Cervical Plexus
The cervical plexus originates from the anterior rami of C1-C4 that combine into 3 loops from which the deep and superficial branches arise (Fig-1).

Deep (muscular) branches:

• The phrenic nerve (C3-C5): innervates the diaphragm
• Nerves to the geniohyoid and thyrohyoid (C1): innervate muscles and soft tissues of the airway
• Ansa cervicalis (C1-C3): supplies muscles important for swallowing and speech

Superficial branches:

• Emerge from the prevertebral fascia in between the longus capitis and the middle scalene muscles to run deep to the sternocleidomastoid muscle (SCM).
• As the SCM forms a "roof" over these branches, they eventually emerge from behind the posterior border of the muscle (Fig-2).
• This occurs approximately at the intersection with the external jugular vein (Erb's point).

The superficial branches of the cervical plexus are:

• Greater auricular nerve
• Lesser occipital nerve
• Transverse cervical nerve
• Supraclavicular nerves

Cross-sectional anatomy

• Cranial to C4, the branches of the cervical plexus are located within the prevertebral fascia in a groove between the longus capitis and the middle scalene muscle (Fig-3).
• At the C4- C5 level, the branches of the cervical plexus are located between the prevertebral fascia, overlying the interscalene groove, and the investing layer of the deep cervical fascia.
• At the C6-C7 level, the branches of the cervical plexus are located superficially to the investing layer of the cervical fascia. 

Ultrasound anatomy

The cervical plexus can be visualized as small oval hypoechoic (dark) nodules immediately deep or lateral to the posterior border of the sternocleidomastoid muscle (SCM) (Fig-4).
The greater auricular nerve can be commonly seen over the SCM as a small, round, hypoechoic structure.

An intermediate cervical plexus block provides sensory anesthesia of the anterolateral neck, retro-auricular areas, and the skin overlying and immediately inferior to the clavicle.

• Patient position: Supine or semi-sitting, with the head turned away from the side to be blocked. This facilitates access to the anterolateral aspect of the neck.
• External landmarks: Posterior border of the sternocleidomastoid muscle at the midpoint between the mastoid process and clavicle.

General considerations:

• For a deep injection: Local anesthetic is injected at the C2-C4 level. This technique blocks the entire plexus and is generally not recommended due to the high risk of complications.
• For an intermediate injection: Local anesthetic is injected at the C4-C5 level, between the prevertebral fascia and the investing layer of the deep cervical fascia, under the sternocleidomastoid muscle (SCM). This is the most common technique used in clinical practice.
• For a superficial injection: Local anesthetic is injected at the level of C6, subcutaneously, superficial to the investing layer of the deep cervical fascia.

INTERMEDIATE CERVICAL PLEXUS BLOCK 

Transducer position

Transverse over the lateral aspect of the neck, overlying the SCM at the midpoint between the mastoid process and clavicle.

Scanning

• Identify the SCM and place the posterior edge in the middle of the screen.

• Slide the transducer cranial and caudally to identify the superficial branches of the cervical plexus as a small collection of hypoechoic nodules (yellow arrows) located under the SCM.

Needle insertion

• Insert the needle in-plane through the skin, platysma, and investing layer of the deep cervical fascia.

• Position the needle tip behind the posterior border of the SCM.
• Inject 1–2 mL of local anesthetic to confirm proper distribution between the fascial layers containing the branches of the cervical plexus.

• Complete the block with 5-8 mL.

Alternative transducer position

• Place the transducer in a coronal orientation over the SCM to obtain a longitudinal view.
• Insert the needle in-plane towards the space behind SCM, superficial to the prevertebral fascia.
• Inject 1-2 mL of local anesthetic to confirm needle position.
• Complete the block with a volume of 5-8 mL.

Let's review the block: 

• The intermediate cervical plexus block provides sensory anesthesia of the neck, without motor block.
• Long-acting local anesthetics are typically used for carotid surgery, while short-acting agents are useful for superficial neck procedures such as node biopsy.

• The “deep” cervical plexus block is basically a cervical paravertebral block, an advanced technique with a high risk of complications.
• The superficial cervical plexus block technique is simpler, safer, and, for most indications adequate.
• In-plane or out-of-plane? The superficial location of the cervical plexus branches makes both approaches possible.
• Do I need to visualize plexus? Not necessarily or always possible.
• Carotid surgery also requires block of the glossopharyngeal nerve branches. This block can be accomplished intraoperatively by injecting the local anesthetic into the carotid artery sheath.