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Intermittent hoarseness with continuous interscalene brachial plexus catheter infusion due to deficient carotid sheath

Sir, Hoarse voice is a common but rarely clinically significant side effect of interscalene brachial plexus block. Incidence varies between 0.8% and 31%, and while the anatomical basis is still debated, it is thought to result from blockade of the recurrent laryngeal nerve (RLN), a branch of the vagus nerve (VN). Presumably, local anaesthetic (LA) tracks between tissue planes to reach the RLN, which lies between the anterolateral oesophageal and posterolateral tracheal surfaces and posterior to the lateral pole of the thyroid before passing under the cricopharyngeus to innervate the larynx. Under normal circumstances, the LA spread should be restricted by the pre-vertebral and pre-tracheal fasciae. The case described later demonstrates hoarseness associated with interscalene block when variant fascial planes are present. A 68-year-old female with a body mass index of 43.2 kg/m presented for shoulder replacement and was managed with general anaesthesia and an interscalene brachial plexus perineural catheter for analgesia. At our institution, interscalene catheterisation is routinely performed under ultrasound guidance with continuous video recording using an in-plane, lateralto-medial approach with a catheter-over-needle system. In this case, the interscalene block was performed with 20 ml of LA (0.5% ropivacaine and 0.125% bupivacaine), 15 ml via the needle and the remaining 5 ml via the catheter to confirm accurate catheter tip position (Fig. 1A). Immediately after completing catheter insertion and stabilisation, the patient complained of hoarseness and poor cough but no respiratory distress. Her neck was re-scanned from the location of the block, anteriorly to the trachea. A continuous collection of LA was noted to extend from the interscalene space, posterior to the anterior scalene muscle and into the carotid sheath, surrounding the internal jugular vein, the common carotid artery, and the VN (Fig. 1B). No LA tracked into the vicinity of the RLN. Surgery was completed uneventfully, and the hoarseness persisted in the recovery room with initially excellent pain relief. The hoarseness progressively resolved during recovery, concordant with increasing shoulder discomfort. A 4-ml bolus of 0.2% ropivacaine resolved the discomfort but also caused recurrence of hoarseness. The patient preferred hoarseness to shoulder pain, and a 0.2% ropivacaine infusion was commenced with a 1-ml/h infusion and 4-ml/h bolus regime. The infusion was ceased 48 h post-operatively, and the patient’s hoarseness resolved within 4 h. She was transitioned successfully to oral analgesia, and the catheter was removed at 72 h post-operatively without recurrence of hoarseness. Upon reviewing the video recording of this procedure, we excluded direct needle penetration of the pre-vertebral fascia or carotid sheath to explain the LA beyond the carotid artery and appearing to surround the VN. It is important to note that the VN appeared relatively large at first glance, which may be partly due to visual enhancement from fluid surrounding nerve and the ultrasound plane being at an oblique angle. Nevertheless, we suggest using minimal LA volumes to reduce unwanted LA spread and recommend post-procedural ultrasound scanning to investigate anatomical variation in cases of complications. Conflicts of interest: The authors declare no conflict of interest.