To the Editor
Ultrasound-guided interscalene block (ISB) is the gold standard for anesthesia and analgesia for shoulder surgery. After emerging from the cervical roots, the brachial plexus (BP) lies between the anterior and middle scalene muscles, and this space is called the interscalene space. It is well known that there are many variations in the anatomy of the BP above the clavicle. Considering that variations can affect the success rate, we need to consider anatomical variations and modify our approach according to relevant anatomy. In this case, our goal was to present our ISB application in a rare interscalene BP variation in a patient scheduled for clavicle surgery.
A right clavicle fracture was scheduled for surgery in an American Society of Anesthesiologists (ASA) physical status I patient, 27 years old, 85 kg, 187-cm tall. The anesthetic plan included ultrasound-guided ISB in the preoperative period and general anesthesia during surgery. In the preoperative period, noninvasive blood pressure, electrocardiogram, and peripheral oxygen saturation were monitored, and 3 mg of midazolam intravenous (IV) was administered as premedication. The patient was placed in the supine position with the head turned to the opposite side. Starting from the supraclavicular area, using a 4 to 12 mHz linear probe, it was observed that the superior trunk entered the anterior scalene muscle (ASM) before reaching the interscalene area. The middle and lower trunks were observed to follow an interscalene course. It was observed that this anatomical variation was not present in the contralateral interscalene BP alignment. Because of this difference, the block was applied in 2 separate planes, as opposed to the general design of the classic ISB. LA was administered in 2 separate planes: 5 mL of 0.25% bupivacaine at the interscalene space and 5 mL of 0.25% bupivacaine for the C5–C6 roots within the ASM. A superficial cervical plexus block using 5 mL of 0.25% bupivacaine was also performed to cover the supraclavicular nerve block (Figure). Perioperative management of the patient followed our routine general anesthetic protocol using 1 minimum alveolar concentration (MAC) of desflurane and 0.01mcg/kg/min of remifentanil for maintenance. The patient received dexamethasone 8 mg IV, ibuprofen 800 mg, and paracetamol 1 gram as part of a multimodal analgesia approach. As part of the patient’s routine analgesia in the postoperative period, IV morphine was scheduled as a 1 mg bolus with an 8-minute lock-in period without patient-controlled analgesia (PCA) infusion dose. Numeric Rank Score (NRS) for pain and total morphine consumption were determined at postoperative hours 1, 6, 12, 18, and 24. There were no additional complications in the patient whose NRS score for pain remained between 0 and 1 throughout the postoperative period. There was no need for rescue analgesia during the first 18 hours. Morphine consumption was 2 mg in 18 to 24 hours.
There are only few case reports in which variations related to C5–C6 have been associated with ASM. There is a classification that the variation within the muscle associated with ASM may be a component of thoracic outlet syndrome (TOS), and anesthesiologists should be aware of this in clinical practice. It has been noted that the occurrence of the scalenus minimus muscle, with an incidence of 4% to 5% may be associated with TOS and BP variations. Our patient’s MRI results were also reviewed, and no pathology was found above the clavicle. The subclavian artery was examined by Doppler USG and no flow problem was found.
In our case, ISB was successfully applied with 2 different injections in a patient with BP variation. Because BP variations can cause technical difficulties and incomplete blocks during ISB, it is very important to prescan the relevant anatomical structures and determine the appropriate block approach before performing the block.