Introduction
The cervical plexus is a network of loops with complicated architecture. It is frequently referred to as the deep and superficial cervical plexus. The muscle branches are supplied by the deep plexus, whereas the skin covering the head and neck is provided by the superficial network. The block is also used in the emergency room for uncomplicated treatments for soft tissue and bone injuries such as ear, neck, and clavicular area injuries, including fractures and dislocations. In addition, we can use this block provides anesthesia for various procedures such as cannulation of the internal jugular vein, biopsies of the lymph nodes of the head and neck region, and surgeries of the thyroid and parathyroid glands. The cervical plexus block is most prevalently used in the case of carotid endarterectomy (to remove the plaque deposits in the carotid artery).
There are three routes to block the cervical plexus, and the blocks may be completed using just landmarks as a reference. The involvement of ultrasonography in the head and neck area has progressed, and cervical plexus blocks (CPBs) may now be conducted more securely and precisely under the guidance of ultrasound, which can quickly detect numerous essential landmarks such as muscles, cervical vertebrae, major arteries and nerves, and the cervical fascia. Because deep cervical plexus block has been linked to significant problems, superficial cervical plexus block is commonly considered adequate for routine surgeries on the neck. Therefore, bilateral deep cervical plexus blocks are never advocated, although bilateral superficial cervical blocks may be utilized successfully for procedures or analgesia postoperatively.
What Is the Anatomy of the Cervical Plexus?
Cervical Fascia: According to Guidera et al., the cervical fasciae can be categorized as a superficial group as well as a deep group; however, instead of utilizing the term ‘superficial cervical fascia,’ the more accurate term ‘subcutaneous tissue’ has been proposed to avoid ambiguity with the superficial layer of the deep cervical fascia. The cervical fascia Is broadly classified Into:
The superficial layer known as the investing fascia but recently known as the masticator fascia, submandibular fascia, or sternocleidomastoid (SCM)-trapezius fascia.
The middle layer proposed as strap muscles or visceral fascia.
The deep layer considered as perivertebral fascia.
Superficial cervical fascia (subcutaneous tissue).
Deep cervical fascia.
The deep cervical fascia can be categorized into:
1. The Carotid Space:
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The carotid space, which contains significant arteries, including nerves, and a cervical group of lymph nodes that are deeply seated, is a critical part that might be damaged during a CPB. It is generally termed the ‘carotid sheath and its components.’
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According to Palliyalil et al., the carotid sheath is a firm fibroelastic tissue barrier that protects its constituents from saliva and local infections following neck surgery, although local anesthetics appear to penetrate the carotid sheath.
2. Cervical Plexus:
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The cervical plexus is formed by a series of loops that connect the upper four cervical nerves. The loops are three in number, C1-2, C2-3, and C3-4, with a fourth loop (C4-5) frequently present to connect the cervical plexus to that of the brachial plexus.
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The cervical plexus is located below the prevertebral fascia in a groove between the longus capitis and the middle scalene muscles.
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Two nerve loops formed by the fusion of the adjoining anterior spinal nerves from 2nd to the 4th cervical vertebrae give rise to four superficial sensory branches, which are mentioned in the craniocaudal sequence as follows: greater auricular (C2, C3), lesser occipital (C2, C3), transverse cervical (C2, C3), and supraclavicular nerves (C3, C4); these run posteriorly and eventually penetrate the prevertebral fascia.
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They then travel via the interfacial region between the SCM and the prevertebral muscles, ultimately reaching the skin and superficial tissues of the neck.
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Therefore, superficial branches of the cervical plexus proceed a pretty long distance from the paravertebral space to their corresponding superficial nerve endings, which include the neck's skin and subcutaneous tissues and the head's posterior portion and shoulders.
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The fibers extending anteromedially from the upper (C1-C2) and lower (C2-C3) roots, on the other hand, merge at the level of the omohyoid central tendon to create a loop called the ansa cervicalis. The motor branches of the infrahyoid and SCM muscles are believed to be supplied by the ansa cervicalis.
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The anterior rami of C3 and C4 form a loop, and the branches of this loop join C5 to give rise to the phrenic nerve. The XI cranial nerve, XII cranial nerve, VII cranial nerve, X cranial nerve, IX cranial nerve, and sympathetic trunk are all recognized to anastomose with the cervical plexus.
What Are the Indications for CPBs?
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The cervical plexus block is recommended when there is a requirement for extensive anesthesia or analgesia to the skin and underlying structure of the anterolateral neck.
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Furthermore, in the anterolateral neck, anesthesia is obtained on the superficial surface of the ear, collar bone, and acromioclavicular joint.
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Carotid endarterectomies, dissection of the lymph nodes in the neck, and superficial neck surgeries are common indications of superficial cervical plexus block.
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It is used in emergency care to install catheters into the internal jugular vein to treat collarbone fractures and restore lacerations and drainage abscesses involving the earlobe and submandibular regions.
What Are the Contraindications for the CPBs?
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Patient unwillingness for the CPB, any ongoing infection covering the site of injection, phrenic nerve paralysis of the phrenic nerve on the opposite side of the neck, preexisting surgeries of the neck, continuous chemotherapy for the neck malignancies, and allergy to local anesthetic drugs, both amide and ester type are all contraindications for superficial cervical plexus block.
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Patients with severe chronic obstructive pulmonary disease or an uncorrected collapsed lung on the opposite side should proceed cautiously since this block tends to affect unexpected phrenic nerve damage.
How Is the Patient Positioned for the CPBs?
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The patient is lying horizontally; semi-sitting (head rotated to the contralateral side) or lateral decubitus (patient lying on one side )are all options.
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The lateral decubitus posture permits the ultrasound to be positioned away from the patient for better quality and to view the screen display.
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While positioning must consider the patient's convenience and limits. For example, the posterior boundary of the SCM might be challenging to recognize in obese persons.
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Request that the patient elevates the head off the bed so that the physician may palpate the posterior border of the SCM.
What Is Landmark-Based Technique?
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A line is traced from the 6th cervical vertebrae to the mastoid process (along the posterior border of the SCM).
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The needle will be inserted at the midway of this line. The superficial cervical plexus branches protrude beneath the sternocleidomastoid muscle's posterior border at this location. The skin is prepared and dressed as usual.
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The local anesthetic is administered against the posterior aspect of the sternocleidomastoid muscle 2 cm to 3 cm beneath and above the needle placement site using a ‘needle fanning’ approach with several needle redirections.
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Avoid deep needle penetration (greater than 1 cm to 2 cm).
What Is an Ultrasound-Based Technique?
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When using the in-plane method, position the high-frequency linear probe in a transversal direction (parallel to the probe axis). This must be performed just above the sternocleidomastoid muscle's posterior border midway.
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This also closely resembles the level of the 4th cervical vertebrae and the thyroid process notch. Therefore, the marker in the probe should be oriented to the medial side of the thyroid cartilage.
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The skin is prepared and draped regularly. Introduce the needle 1 cm to 2 cm from the lateral to medial aspect under the posterior margin of the sternocleidomastoid muscle. The needle should be inserted into the thyroid cartilage level.
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As the cervical plexus is located inside this dense fascial layer, arrange the needle tip to deliver local anesthetic immediately deep to the posterolateral curving sternocleidomastoid muscle and above the levator scapula muscle.
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The needle tip should not exceed 2 centimeters deep to avoid accidental administration into surrounding structures. Inject roughly 5 milliliters to 10 milliliters of local anesthetic by immediately viewing the needle tip to prevent accidental intravascular administration.
What Are the Complications of the CPBs?
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Accidental intravascular administration of local anesthetic may result in systemic toxicity. Therefore, before administering the superficial cervical plexus block, you must be knowledgeable in addressing local anesthetic systemic toxicity.
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Unintentionally deep injections or large volumes of local anesthetic can develop recurrent laryngeal nerve, phrenic nerve, deep cervical plexus, and brachial plexus dysfunction or blockade.
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When the accessory nerve is inadvertently blocked, this could induce sternocleidomastoid and trapezius muscle weakness. It is also common to pierce the internal jugular vein and the carotid artery. The use of ultrasonography can assist in minimizing the damage.
Conclusion
Cervical plexus blocks are straightforward to learn, and their indications are growing. Although carotid endarterectomy is still the most prevalent rationale for this block, it has recently been used by emergency care units and for chronic pain management in the head and neck region. Most individuals adopt landmark approaches. However, with current advancements, these blocks may now be performed efficiently with the help of ultrasound guidance. Interdisciplinary team cooperation between physicians, nurses, and pharmacists will guarantee that the proper patient is prepared and given the suitable volume of the correct drug for the procedure.
