Brachial plexus: sonoanatomy

Which of the following statements regarding sonoanatomy of the brachial plexus is NOT true?

A. As many as 1/3rd of patients have a C5 nerve root that travels through the anterior scalene muscle prior to joining the C6 root to form the superior trunk.
B. Branches from the thyrocervical trunk, frequently the transverse cervical artery, may pass across the brachial plexus above the clavicle and should be kept in mind and identified when performing supraclavicular and interscalene nerve blocks.
C. Axillary veins are easily compressed when performing an axillary nerve block and may not be apparent even when aspirating prior to injection of local anesthetic.
D. A ‘double bubble’ sign of local anesthetic inferior to the axillary artery is associated with a high rate of success for the infraclavicular block.
E. All of the above statements are TRUE

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Correct Answer: E

Explanation:

The sonoanatomy of the brachial plexus has helped to highly the variability of nerve location at a population-based level. Up to 35% of patients may have a separation of the C5 nerve root from the C6 and C7 roots. The C5 root then runs through the anterior scalene muscle to join the other roots as the superior trunk, leading some to propose a modification of the traditional interscalene block at the level of the three roots to a targeted superior trunk block. The transverse cervical artery frequently runs longitudinally in the same vicinity of the ultrasound probe when performing a supraclavicular block. Modification of approach to the brachial plexus may be necessary when identifying this arterial structure. Negative aspiration prior to the injection of local anesthetic does not preclude intravenous needle location, especially if the vein and/or needle are small. Different approaches to the infraclavicular block have been described but one with a reasonably high rate of success involves placement of local anesthetic inferior to the axillary artery, creating the so-called ‘double bubble’ sign. Another effective location for infraclavicular blockade is more proximally, immediately beneathe the clavicle, where the cords of the brachial plexus lie superior, posterior and lateral to the artery, in a tighter conformation, allowing for a single injection of local anesthetic between the cords. Care must be taken to avoid the pleura with the proximal infraclavicular approach.

References:

Burckett-St. Laurant D et al. Refinding the ultrasound-guided interscalene brachial plexus block: the superior trunk approach. Can J Anesth 2014;61:1098-1102.

Robards C et al. Intravascular injection during ultrasound-guided axillary block: negative aspiration can be misleading. Anesth Analg 2008:107:1754-5.

Sala-Blanch X, Reina MA, Pangthipampai P, Karmakar MK. “Anatomic bases for brachial plexus block at the costoclavicular space: a cadaver anatomic study.” Reg Anesth Pain Med 2016;41:387-91.

Tran DQH et al. A comparison between ultrasound-guided infraclavicular block using the “double bubble” sign and neurostimulation-guided axillary block. Anesth Analg 2008;107:1075-1078.

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