Ultrasound standard of peripheral nerve block for shoulder arthroscopy: a single- penetration double-injection approach targeting the superior trunk and supraclavicular nerve in the lateral decubitus position    British Journal of Anaesthesia  Volume 116, Issue 4, Pages 574-575 (April 2016) DOI: 10.1093/bja/aev459 Copyright © 2016 The Author(s) Terms and Conditions

Fig 1 The single-penetration double-injection approach to peripheral nerve block for shoulder arthroscopy. To help illustrate the structures within the axial sonogram in the lateral decubitus position (a and b), a sketch (c) is made corresponding to the pre-injection sonogram (b). The prevertebral fascia extends laterally on scalenus anterior, the brachial plexus, and scalenus medius, forming the floor of the posterior neck triangle (b; yellow arrows). The fascial plane on the surface of scalenus medius where the supraclavicular nerve resides crosses the line connecting the puncture site and superior trunk (a), thus facilitating a single-penetration double-injection approach, with one injection posterior to the superior trunk and the other over scalenus medius (d). At the superior trunk level, arterial puncture should be avoided by finding the needling plane without the transverse cervical artery lying above the superior trunk (a, b and c) during the prescan. With the long axis of the transducer oriented along the visual axis (a), the needle is inserted in-plane lateral to sternocleidomastoid toward the superior trunk, as shown by the white dashed line in the sonogram (a) and the green dotted arrow in the sketch (d). The needle should be redirected if any muscle contraction occurs while traversing scalenus medius. After spreading around the superior trunk (d; the blue shaded area within the interscalene groove indicating the spread of injectate from the dotted green needle tip), the needle is then pulled back to place its tip (the solid green arrow) over the prevertebral fascia above scalenus medius (d). Not only indicated for the superior trunk block, the opening pressure test13 is also recommended for the usually invisible supraclavicular nerve. By using the convenient alternative,19 the volume consumed to confirm the correct plane to be dissected could be 5% dextrose water instead of local anaesthetic. Fascial plane dissection is deemed adequate if the test volume separates the prevertebral fascia from the above connective tissue superficial to scalenus medius and the superior trunk, but not scalenus anterior (d; blue shaded area over the prevertebral fascia indicating the spread of injectate from the solid green needle tip) to prevent accentuation of phrenic nerve paralysis by a real-time assessment of local anaesthetic spread.10 Scalenus medius is usually displaced downward by the spread (d). EJ, external jugular vein; MSM, middle scalene muscle; SCM, sternocleidomastoid muscle; ST, superior trunk. British Journal of Anaesthesia 2016 116, 574-575DOI: (10.1093/bja/aev459) Copyright © 2016 The Author(s) Terms and Conditions