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The Speed of Sound

The Speed of Sound: Ultrasound-Guided Interscalene Blocks Reduce Observation Time for Shoulder Reductions

Butts, Christine MD

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doi: 10.1097/01.EEM.0000453163.47158.2b
    Image 1
    Image 1:
    Image 1. Placement of the transducer to best visualize the brachial plexus trunks. Slightly rotating the transducer to an oblique orientation may enhance visualization of the anatomy.

    A 25-year-old man presents to the ED with a complaint of left shoulder pain. He says he fell out of bed and onto his shoulder. He has a history of multiple prior dislocations and feels that it is dislocated again. An x-ray demonstrates an inferiorly dislocated humeral head without fracture.

    Traditionally, some combination of medications has been used to facilitate shoulder reductions. This method is usually successful, but it can be time-consuming, particularly after the procedure because the patient typically must be observed for a time. Ultrasound-guided interscalene nerve blocks offer an alternative to traditional sedation without the need for prolonged post-procedure observation.

    A high-frequency transducer should be used to achieve maximum resolution at a superficial depth. The trunks of the brachial plexus can be found lateral to the internal jugular vein and carotid artery. Identifying these vascular structures at the level of the thyroid in the transverse orientation makes a good starting point. (Image 1.)

    Moving the transducer laterally, the anterior scalene muscle can be identified, followed by the middle scalene. (Image 2.) Once these muscles have been identified, the transducer can be rotated slightly to an oblique plane, which should allow the trunks of the brachial plexus to be visualized. They will appear as hypoechoic (dark gray) rounded structures with a surrounding hyperechoic (white) border, and will lay in a row. These are C5, C6, and C7 from superficial to deep. These trunks at times may resemble vascular structures. Color flow can confirm that they are not vessels.

    Image 2
    Image 2:
    Image 2. Anatomy of the area surrounding the brachial plexus. The internal jugular (IJ) and carotid artery (CA) with overlying sternocleidomastoid (SCM) can be seen on the right of the image. Lateral to these structures, the anterior scalene (AS) and middle scalene (MS) muscles can be seen with the brachial plexus trunks appearing in between.

    Once the trunks have been identified, the ultrasound should be used to directly guide placement of anesthetic solution into the area surrounding the trunks. An in-plane technique, where the needle is inserted along the long axis of the transducer, is preferred, so that the entire needle and tip can be visualized as it advances toward the trunks. Anesthetic solution should be injected around each of the trunks in a circumferential manner as close as possible to the nerves without puncturing the nerves themselves. The closer the solution can be injected, the less volume that is needed. Typically, about 5–10 ccs of solution is needed surrounding each trunk. The block takes approximately 10–20 minutes to take effect, and will last a variable amount of time, depending on which type of anesthetic is used.

    Anesthetizing the C5, C6, and C7 trunks will provide excellent anesthesia of the shoulder and facilitate reduction. A prospective and randomized study by Blaivas, et al. in Academic Emergency Medicine compared ultrasound-guided interscalene blocks with moderate sedation for shoulder reduction, and found no statistically significant difference in patient satisfaction or in pain during the procedure. A difference was noted in length of stay, with moderate sedation patients staying significantly longer. (2011;18[9]:922.)

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