Intermediate cervical plexus block

Intermediate. The target plane is easy to see, but the carotid artery, internal jugular vein and the prevertebral fascia are close, so careful needle control is needed.

The neck has three layers of deep cervical fascia that matter here: the investing layer, which wraps sternocleidomastoid; the prevertebral layer, which covers the scalene and levator scapulae muscles and the roots of the plexuses; and the carotid sheath.

The sensory branches of the cervical plexus leave the plexus under the prevertebral fascia, pass through it, and then run in the space between it and the investing fascia (the posterior cervical space) before winding round the back edge of sternocleidomastoid.

An intermediate block puts the drug in this space, under sternocleidomastoid but on top of the prevertebral fascia. The prevertebral fascia should keep the drug away from the phrenic nerve and the roots, which lie deep to it.

Drug in this space often spreads medially towards the carotid sheath, which may help during carotid surgery.

• Mastoid process.
• Back edge of sternocleidomastoid at its midpoint (about the level of the thyroid cartilage, C4).
• External jugular vein.
• Carotid pulse (medial, to stay away from).

• Carotid endarterectomy under regional anaesthesia (with surgical top-up near the jaw and the carotid bifurcation).
• Thyroid and parathyroid surgery, for analgesia.
• Neck dissection skin and lymph node surgery.
• Clavicle surgery, together with an interscalene or superior trunk block.

• Lesser occipital, great auricular, transverse cervical and supraclavicular nerves (C2–C4)
• Sometimes branches of the ansa cervicalis and small twigs to the carotid sheath

Surface anatomy, relevant structures and landmarks

Mark the midpoint of the back edge of sternocleidomastoid, as for the superficial block.

Positioning

Supine with the head turned 30–45° away.

Block technique

• Insert a short-bevel needle at the back edge of the muscle, aiming under it.
• Feel a 'pop' as the needle passes through the investing fascia, then inject 10–15 mL after aspiration.
• Ultrasound is strongly preferred, because the depth of the plane varies.

Needle choice

22 G short-bevel, 50 mm.

Neurostimulation technique

Not used.

Choice of local anaesthetic (including volume)

• 10–15 mL of 0.25–0.5% levobupivacaine, 0.375–0.5% ropivacaine or a lidocaine and long-acting mixture for carotid surgery.
• Keep the total dose (including the surgeon's top-up) within the maximum: use the dose calculator.

Show scan

IL Investing layer of the deep cervical fasciaSCP Superficial cervical plexusPVF Prevertebral fasciaSCM SternocleidomastoidASm Anterior scalene muscleC5 C5 nerve rootC6 C6 nerve rootMSm Middle scalene muscleIJV Internal jugular veinCar.A Carotid arteryC7 C7 nerve rootVe.V Vertebral veinVe.A Vertebral arteryC7 TP C7 transverse processLCm Longus colli musclePhN Phrenic nerveDSN Dorsal scapular nerveLTN Long thoracic nerve

Positioning

As above, with the screen on the other side of the patient.

Scanning technique

• Place the probe across the neck at C4 over sternocleidomastoid; find the carotid artery and internal jugular vein under the muscle.
• Slide laterally until the tapering back edge of sternocleidomastoid is in the middle of the screen.
• Identify the bright prevertebral fascia over levator scapulae and the scalene muscles, and the small nerve branches lying on it.
• Use colour Doppler to check the needle path.

Structures to identify

• Sternocleidomastoid and its investing fascia
• Prevertebral fascia
• Cervical plexus branches in the posterior cervical space
• Levator scapulae and middle scalene
• Carotid artery and internal jugular vein (medial)
• External jugular vein (superficial)

Position / ergonomics

Stand at the head of the bed or on the side of the block.

Probe

Linear, high frequency.

Settings

Nerve or small parts preset, depth 3 cm.

Depth

1–2.5 cm.

Needle size

22 G, 50 mm short-bevel.

Needling technique

In-plane from lateral to medial, passing under the back edge of the muscle.

Optimal needle-tip position

Under sternocleidomastoid and on top of the prevertebral fascia. The drug should lift the muscle off the fascia. If it spreads under the prevertebral fascia, stop and pull back: that is a deep block, with a higher risk of phrenic nerve block.

Drug choice

As above.

Volume

10–15 mL.

Optimal current if nerve stimulation is used

Not used.

Muscle responses acceptable

Not applicable.

Testing block success

• Loss of sensation over the front and side of the neck, ear lobe and clavicle
• Comfort when the surgeon cuts the skin

Rarely used. Catheters in this space have been described for major neck surgery but are not standard.

• Watch the drug lift sternocleidomastoid off the prevertebral fascia; if it disappears deep, stop.
• For carotid surgery, plan the surgeon's top-up into the total dose from the start.
• Avoid bilateral intermediate blocks in patients who rely on both hemidiaphragms.
• Trials comparing it with a subcutaneous (superficial) block for carotid surgery found similar results, so choose the one you do most safely.

• Pandit and colleagues (2007) found superficial and intermediate blocks safer than deep or combined blocks for carotid endarterectomy, with fewer conversions to general anaesthesia.
• Ramachandran and colleagues (2011) randomised 44 patients having carotid endarterectomy to an intermediate or a subcutaneous block: the surgeon's lidocaine top-up and patient satisfaction were similar.
• Kim and colleagues (2018) explained why the name 'intermediate' has caused confusion, and described the fascial compartments seen on ultrasound.

• Pandit JJ, Satya-Krishna R, Gration P. Superficial or deep cervical plexus block for carotid endarterectomy: a systematic review of complications. Br J Anaesth 2007;99:159–169. PubMed
• Ramachandran SK, Picton P, Shanks A, Dorje P, Pandit JJ. Comparison of intermediate vs subcutaneous cervical plexus block for carotid endarterectomy. Br J Anaesth 2011;107:157–163. PubMed
• Kim JS, Ko JS, Bang S, Kim H, Lee SY. Cervical plexus block. Korean J Anesthesiol 2018;71:274–288. PubMed