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The Speed of Sound

The Speed of Sound: Visualizing Radial Nerve for Anesthesia Made Easy with Ultrasound

Butts, Christine MD

Author Information
doi: 10.1097/01.EEM.0000455724.07503.fe
    Image 1
    Image 1:
    Image 1. Place the transducer proximal to the elbow to visualize the radial nerve.

    Regional anesthesia of the hand and wrist traditionally has been done using landmark-guided median, ulnar, and radial nerve blocks at the wrist. Ultrasound, however, can be used as an alternative to visualize the nerve directly and to guide placement of anesthetic in the forearm.

    The radial nerve provides sensation to the dorsum of the thumb, index, and middle fingers as well as the radial aspect of the hand. It carries motor and sensory fibers, and, importantly, divides into sensory and motor branches around the elbow. The sensory and motor branches travel together to approximately the distal forearm, where they divide into multiple smaller branches to innervate the hand. The radial nerve can be blocked in multiple locations, either above the elbow or in the proximal forearm.

    A high-frequency transducer should be used to obtain maximum resolution at a superficial depth. Visualize the nerve proximal to the elbow by placing the transducer on the anterior aspect of the distal arm. Having the patient flex at the elbow with his forearm resting against his side provides good positioning for the EP. The transducer is placed in the transverse orientation about 3-4 cm proximal to the elbow crease on the anterolateral aspect of the arm. (Image 1.) The nerve is visualized as a hyperechoic (bright white) slightly triangular bundle deep to the bicep and lateral to the humerus. (Image 2.)

    Image 2
    Image 2:
    Image 2. The radial nerve (arrow) is seen as a hyperechoic triangular object deep to the bicep (B) and adjacent to the humerus (arrowhead).

    Visualize the nerve distal to the elbow by placing the transducer in the transverse orientation over the radial aspect of the proximal forearm. (Image 3.) The radial artery serves as a good starting landmark. The nerve can be seen as an oval or slightly triangular hyperechoic structure lateral to the artery. (Image 4.)

    Image 3
    Image 3:
    Image 3. Place the transducer distal to the elbow to visualize the radial nerve.
    Image 4
    Image 4:
    Image 4. The radial nerve (arrow) is seen as a hyperechoic triangular object adjacent to the radial artery (arrowhead).

    Once the nerve has been identified in either location, an in-plane approach can be used to inject anesthesia directly around the radial nerve. The needle is inserted in the in-plane approach from the long end of the transducer, so that the needle tip can be visualized as it approaches the nerve. Inject the anesthesia once the needle tip is seen adjacent to the nerve. The fluid should be seen to cover the superficial aspect of the nerve and typically no more than 8 cc is needed. The patient should achieve anesthesia within 15-20 minutes depending on the type of anesthetic used.

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