CERVICAL PLEXUS BLOCK AT A GLANCE
• Indications: carotid endarterectomy, superficial neck surgery (Figure 1)
• Transducer position: transverse over the midpoint of the sternocleidomastoid muscle (posterior border)
• Goal: local anesthetic spread around the superficial cervical plexus or deep to the sternocleidomastoid muscle
• Local anesthetic: 5–15 mL
The goal of the ultrasound (US)-guided technique of superficial cervical plexus block is to deposit local anesthetic within the vicinity of the sensory branches of the nerve roots C2, C3, and C4 (Figures 2 and 3). Advantages over the landmark-based technique include the ability to visualize the spread of local anesthetic in the correct plane, which therefore increases the success rate, and to avoid a needle insertion that is too deep and the inadvertent puncture of neighboring structures.
Both US-guided superficial and deep cervical plexus blocks have been well described. The deep cervical plexus block is an advanced block with a risk of potentially serious complications, such as intrathecal injection or injection into the vertebral artery. For this reason, we will focus primarily on the superficial cervical plexus block technique. It is simpler, safer, and, for most indications, it is equally as suitable as the deep cervical plexus block. An understanding of the fascial planes of the neck and the location of each of these blocks is necessary (Figure 2). For the superficial cervical plexus block, local anesthetic is injected superficially to the deep cervical fascia. For the superficial (intermediate) cervical plexus block, the injection is made between the investing layer of the deep cervical fascia and the prevertebral fascia, whereas for the deep cervical plexus block, local anesthetic is deposited deep to the prevertebral fascia.
The sternocleidomastoid muscle (SCM) forms a “roof” over the nerves of the superficial cervical plexus (C2–4) (see Figure 2). The roots combine to form the four terminal branches (the lesser occipital, greater auricular, transverse cervical, and supraclavicular nerves) and emerge from behind the posterior border of the SCM (Figures 3, 4 and 5). The plexus can be visualized as a small collection of hypoechoic nodules (honeycomb appearance or hypoechoic [dark] oval structures) immediately deep or lateral to the posterior border of the SCM (see Figure 5), but this is not always apparent.
Occasionally, the greater auricular nerve is visualized on the superficial surface of the SCM as a small, round, hypoechoic structure. The SCM is separated from the brachial plexus and the scalene muscles by the prevertebral fascia, which can be seen as a hyperechoic linear structure. The cervical plexus lies posterior to the SCM and immediately superficial to the prevertebral fascia overlying the interscalene groove (see Figure 5). Strictly speaking, the technique we describe, with an injection between the investing layer of the deep cervical fascia and the prevertebral fascia, is thus an intermediate cervical plexus block.
DISTRIBUTION OF ANESTHESIA
The superficial cervical plexus block results in anesthesia of the skin of the anterolateral neck and the ante-auricular and retroauricular areas, as well as the skin overlying and immediately inferior to the clavicle on the chest wall Figures 1 and 6). The mental, infraorbital, and supraorbital nerves are branches of the trigeminal nerve and are not blocked with cervical plexus block.
The equipment needed for a cervical plexus block includes the following:
• Ultrasound machine with a linear transducer (8–18 MHz), sterile sleeve, and gel
• Standard nerve block tray
• A 10-mL syringe containing local anesthetic
• A 5 cm, 23- to 25-gauge needle attached to low-volume extension tubing
• Sterile gloves
LANDMARKS AND PATIENT POSITIONING
Any patient position that allows for comfortable placement of the ultrasound transducer and needle advancement is appropriate. This block is typically performed in the supine or semi-sitting position, with the head turned slightly away from the side to be blocked to facilitate operator access (Figure 7). The patient’s neck and upper chest should be exposed so that the relative length and position of the SCM can be assessed. The posterior border of the SCM can be difficult to locate, especially in obese patients. Asking the patient to lift his or her head off the bed can facilitate palpation of the posterior border of the SCM.
The goal of this block is to place the needle tip in the fascial layer underneath the SCM adjacent to the cervical plexus, which is contained within the tissue space between the Cervical fascia and posterior sheath of the SCM. If the elements of the cervical plexus are not easily visualized, the local anesthetic can be deposited in the plane immediately deep to the SCM and superficial investing layer of deep cervical fascia and superficial to the prevertebral fascia. A volume of 5-10 mL of local anesthetic usually suffices.
With the patient in the proper position, the skin is disinfected and the transducer is placed on the lateral neck, overlying the SCM at the level of its midpoint (approximately the level of the cricoid cartilage).
Once the SCM has been identified, the transducer is moved posteriorly until the tapering posterior edge is positioned in the middle of the screen. At this point, an attempt should be made to identify the brachial plexus and/or the interscalene groove between the anterior and middle scalene muscles. The cervical plexus is visible as a small collection of hypoechoic nodules (honeycomb appearance) immediately superficial to the prevertebral fascia that overlies the interscalene groove (see Figure 2 and 5).
Once the plexus has been identified, the needle is passed through the skin, platysma, and investing layer of the deep cervical fascia, and the tip is placed adjacent to the plexus (Figure 8). Because of the relatively shallow position of the target, both in-plane (from the medial or lateral sides) and out-of-plane approaches may be used. Following negative aspiration, 1–2 mL of local anesthetic is injected to confirm the proper injection site. The remainder of the local anesthetic (5–15 mL) is administered to envelop the plexus (Figure 9).
If the plexus is not visualized, an alternative substernocleidomastoid approach may be used. In this case, the needle is passed behind the SCM, and the tip is directed to lie in the space between the SCM and the prevertebral fascia, close to the posterior border of the SCM (Figures 7b, 10 and 11). Local anesthetic (5–15 mL) is administered and should be visualized layering out between the SCM and the underlying prevertebral fascia (Figure 12). If the injection of local anesthetic does not appear to result in an appropriate spread, needle repositioning and further injections may be necessary. Because the cervical plexus is made up of purely sensory nerves, high concentrations of local anesthetic are usually not required; ropivacaine 0.25–0.5%, bupivacaine 0.25%, or lidocaine 1% is a sufficient
Visualization of the plexus is not necessary to perform this block because the plexus may not always be readily apparent. Administration of 10 mL of local anesthetic deep to the SCM provides a reliable block without the position of the plexus needing to be confirmed.
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