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How To Do a Radial Nerve Block
Step by Step Description of Procedure
Check sensation and motor function of the radial nerve. Wear gloves and use appropriate barrier precautions. Palpate the radial artery at the radial styloid. Needle-entry site:The needle will be inserted just lateral to the radial artery at the proximal wrist crease. Cleanse the site with antiseptic solution. Place a skin wheal of anesthetic, if one is being used, at the needle-entry site. Insert the needle and advance it equal to the depth of the artery. If paresthesia occurs during insertion,withdraw the needle 1 to 2 mm, aspirate to exclude intravascular placement, and then slowly (ie, over 30 to 60 seconds) inject about 2 mL of anesthetic. If paresthesia does not occur,aspirate and then slowly inject about 2 to 5 mL of anesthetic. Next, anesthetize the dorsal branches of the radial nerve: Withdraw and reposition the needle. Then inject another 5 mL of anesthetic subcutaneously from the initial insertion site to the dorsal midline of the wrist. Allow about 5 to 10 minutes for the anesthetic to take effect. Set the ultrasound machine to 2-D mode or B mode. Adjust the screen settings and probe position if needed to attain an accurate left-right orientation. This almost always means orienting the side-mark on the probe to the operator's left side (corresponding to the left-sided marker dot/symbol on the ultrasound screen). Cleanse the sides and volar surface of the wrist with antiseptic solution. Cover the probe tip with a layer of gel, then cover the tip with a sterile transparent dressing tightly (to eliminate air bubbles underneath). Apply sterile lubricant to the covered tip. Place the probe tip transversely (short-axis, cross-sectional view) on the proximal wrist crease. Adjust the gain on the console so that the blood vessels are hypoechoic (appear black on the ultrasound screen) and the surrounding tissues are gray. Nerves appear as an echogenic (white), honeycombed, triangular shape, often adjacent to an artery. Adjust maximum depth to roughly twice the distance from the surface to the radial artery. Slide the probe transversely as needed to center the artery on the ultrasound screen. Identify the radial nerve laterally adjacent to the artery. Slowly slide the probe up the wrist to more clearly see the nerve and artery, with some space between them. Move the probe proximal to the distal third of the forearm to ensure placement of the block proximal to the superficial cutaneous nerve branches. Do not move the probe from this spot. Insert the needle and slightly tilt/rotate the probe to view the needle on the ultrasound screen (an in-plane, longitudinal image). Maintaining the entire longitudinal needle image on the screen, advance the needle tip close to the nerve. Inject a small test dose of anesthetic (about 0.25 mL) to see whether it spreads around the nerve. If not, move the needle position closer to the nerve and inject another test dose. When the needle tip is properly positioned, inject 1 to 2 mL of anesthetic solution to further surround the nerve. If necessary, reposition the needle tip and inject more small amounts; however, the donut sign—nerve completely surrounded by anesthetic—is not required. 