Nerve stimulator‐guided cervical plexus block for carotid endarterectomy

Abstract

Regional anaesthesia for carotid artery surgery allows the patient to remain awake so that the neurological status can be assessed during cross-clamping. However, this technique is unfamiliar to many anaesthetists and, even in experienced hands, failure may occur [1, 2]. We describe a simple modified technique based on a three-injection technique as described by Moore [3]. The patient is placed in the semi-sitting position with their head turned slightly away from the side to be blocked. The transverse processes of C2, C3 and C4 are located approximately 1 cm posterior to the posterior border of the sternomastoid muscle, and intradermal infiltration of lidocaine 1% 0.25 ml for each level is performed. The deep cervical plexus block is performed using a short-bevelled needle (50 mm-Stimuplex; B Braun, Melsungen, Germany) connected to a nerve stimulator (Stimuplex DIG, B Braun), and the needle inserted perpendicular to the skin, aiming in a slightly caudal direction at the C2 level to elicit neck muscle contractions. The same technique is repeated at C3 and C4. The tip of the needle is considered to be correctly positioned when a current intensity of 0.5 mA elicits a neck muscle response. Five ml of local anaesthetic mixture (bupivacaine 0.5% and lidocaine 2%) is injected over 2–3 min after a negative aspiration test. The technique is completed by performing a superficial cervical plexus block by infiltration at the midpoint of the sternomastoid muscle with 7 ml of the same mixture and infiltration of 3–5 ml of local anaesthetic mixture along the inferior border of the mandible to block the afferent branches from the cranial nerves. This injection along the mandible appears to reduce the pain associated with prolonged use of a retractor. We have found that patients are rarely distressed or uncomfortable during performance of these blocks. We have obtained excellent results with this technique in a number of patients and further evaluation is ongoing. The use of a nerve stimulator for deep cervical plexus blockade has been previously reported for carotid surgery. Mehta and Juneja [4] and Merle et al. [5] used a single-injection technique, guided by a nerve stimulator. In both reports the technique was not completely successful and required supplemental intravenous analgesia or local anaesthetic infiltration, particularly during retractor placement and carotid artery dissection. In our technique, the identification of nerves of the cervical plexus was more precise, requiring neck muscle contraction prior to each of the three injections. Phrenic nerve palsy is frequent (up to 90%) after deep cervical plexus block. The use of a nerve stimulator can elicit a diaphragmatic muscle response which helps to avoid the administration of the local anaesthetic directly into the area of the phrenic nerve. It has been reported that the use of a nerve stimulator decreases the peak serum concentration (Cmax) and significantly slows the time to reach peak concentration (Tmax) of the local anaesthetic [5], both of which are major determinants of systemic toxicity.