Carotid endarterectomy is performed to prevent embolic strokes in patients with significant carotid stenosis. The North American Symptomatic Endarterectomy Trial (NASCET) and the European Carotid Surgery Trial (ECST) are two large, randomized trials that compared surgery with best medical management [6, 7]. Combined, the data from both studies revealed 16% and 4.6% reductions in the absolute risk of stroke for more than 5 years when carotid occlusion was > 70% and > 50%, respectively. NASCET indicates surgery once the occlusion is > 50%, and ECST indicates surgery when the occlusion is > 70%. Both criteria suggest performing surgery within two weeks of symptom onset for greatest risk reduction. Five patients included in this case series had symptomatic carotid obstructions of more than 70%, making them suitable for carotid endarterectomy.

CEA can be performed under general anesthesia (GA) or regional anesthesia (RA). The GALA trial, which compared GA vs. RA, showed no difference in primary or secondary outcomes following CEA [3]. Therefore, the choice of anesthesia should be individualized according to the patient. Most centers utilize GA for this procedure [8]. The advantages of GA over RA include better control of CO2 and hemodynamic parameters [3, 9]. Patients who are unable to lie flat or who have chronic cough cannot undergo RA for CEA. GA is indicated for these patients.

RA has the advantages of enabling continuous neurological monitoring during surgery and being able to be performed in patients who are not fit for GA. Poor patient compliance, movement of the surgical site due to patient movement, inability to proceed in claustrophobic patients and patients with respiratory symptoms/cough, anxiety-related effects (tachycardia, hypertension, myocardial ischemia, elevated cerebral metabolic rate), risk of conversion to GA and risks associated with regional block are the disadvantages associated with RA [10, 11]. In contrast, GA reduces the cerebral metabolic rate, hence reducing oxygen consumption. However, other means of monitoring cerebral perfusion, such as electroencephalogram, jugular venous oxygen tension, transcranial Doppler and carotid artery stump pressure, are needed. Most centers may not have the facilities to monitor these functions, and they will not detect subtle changes in consciousness. Therefore, the choice of GA vs. RA has to be individualized.

The available methods for accessing the RA are cervical epidural, posterior cervical paravertebral block and cervical plexus blocks. The first two are not commonly used due to their significant side effects [12]. Common choices for cervical plexus blocks for CEA are superficial blocks alone or a combination of superficial and deep blocks. These are supplemented by direct infiltration of tissue planes by the surgeon as they dissect. Studies have shown that there is no significant difference between the two types of blocks with regard to the amount of local anesthetic supplementation.

The anatomy of the cervical plexus and fascial sheaths in the neck is complex, but it is important to study when disease spread, infection and regional anesthesia are considered [13]. The cervical plexus is situated between the longus capitis and the middle scalene muscles. Two nerve loops, formed by the union of the anterior spinal nerves from C2 to C4, give off four superficial sensory branches: the lesser occipital (C2, C3), great auricular (C2, C3), transverse cervical (C2, C3), and supraclavicular nerves (C3, C4); these branches initially run posteriorly and soon pierce the prevertebral fascia [14, 15]. These nerves pass through the prevertebral muscles and reach the skin at the posterior border of the sternocleidomastoid muscle. The deposition of local anesthetics at this point is considered a superficial cervical plexus block (SCB) that provides adequate analgesia in most neck surgeries.

A deep cervical plexus block (DCB) is performed at the paravertebral space targeting the C2-C3 nerve roots. This can be performed as a single shot or three different injections [13, 16]. Despite providing adequate analgesia, this block can cause serious complications. Phrenic nerve palsy, intravascular injections to major neck vessels, and epidural and subarachnoid injections are among these complications. The use of ultrasound can minimize some of these complications [17].

Intermediate cervical plexus blocks (ICPB) are relatively underused for neck surgeries. It was first described in 2004 by Telford and Stoneham [18]. The ICPB is the area where the deep cervical plexus penetrates the prevertebral fascia and branches deep to the sternocleidomastoid muscle to migrate to the superficial cervical plexus. This block has been widely used in patients undergoing thyroidecyomy for postoperative pain relief [16]. Few cases of its use for CEA have been reported [4, 5]. The ultrasound technique can be used as an anterior approach or a posterior approach. There are studies describing the use of the posterior approach and anterior approach of ICPB for carotid surgery [4, 5]. We used the posterior approach, keeping the patient in the lateral position and allowing free space for mobilization of the needle. Traditionally ICPB is performed at the level of C4. But we performed at the level of C6, that is at the level of the cricoid cartilage. This level was selected to avoid the C4 level as most carotid plaques occur at the level of carotid bifurcation, which is located at C4 and in case of inadvertent arterial puncture, we could disturb the plaque. However with the use of 8 ml of anaesthetic solution, we could see the adequate spread up to C4 level.

In contrast to the literature, we used a combination of superficial and deep cervical plexus blocks for carotid surgeries. On some occasions, the ICPB may not cover the area supplied by the marginal mandibular nerve, which can cause discomfort to the patient due to the use of retractors during surgery. The SCBPs cover this area. None of our patients complained of pain due to the use of retractors.

The operative field of the CEA lies inside the carotid sheath. The carotid sheath is composed of a tight fibrous band that is less penetrative to substances, particularly infections [9]. However, it has been shown that local anesthetics penetrate through the sheath to provide anesthesia. This makes RA a favorable option for CEA. ICPB deposits local anesthetics close to the carotid sheath, enabling adequate anesthetics.

In comparison to DCPB, ICPB is relatively easy block to perform and can be done with single injection whereas DCPB may require 3 injections at different levels. The ICPB is not associated with sinister complications like epidural or subarachnoid injections or accidental vertebral artery injection which may affect the continuation of surgical procedure. Considering these factors ICPB is a safe and easy option than DCPB.

We observed fluctuations in hemodynamics during surgery in all patients. A randomized controlled trial will show whether these changes are significant in comparison to those in GA. This would be a good area to explore in further studies.

The aim of this case series is to show the adequacy of combination of SCPB and ICPB to perform CEA and to analyse the potential complications associated with it. In conclusion, ICPB in combination with SCPB provides adequate anesthesia for CEA surgeries and can be used safely in compromised patients who do not withstand GA or in situations where cerebral monitoring is not available. The SCPB is relatively easy to perform and is not associated with serious complications like intra cranial spread or phrenic nerve palsy as in DCPB. However, further studies are needed to compare the hemodynamic effects and complications of the block compared to those of GA and DCPB.