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How To Do an Ulnar Nerve Block
Step by Step Description of Procedure
Check sensation and motor function of the ulnar nerve. Wear gloves and use appropriate barrier precautions. Locate the flexor carpi ulnaris tendon by palpating just proximal to the pisiform bone as the patient flexes the wrist against resistance. The needle-entry site:The needle will be inserted horizontally into the ulnar side of the wrist at the proximal flexor crease, under the flexor carpi ulnaris tendon and distal to the ulnar styloid. 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 horizontally, under the flexor carpi ulnaris tendon, and advance it about 1 to 1.5 cm laterally (radially) toward the ulnar nerve.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 3 to 5 mL of anesthetic. Next, anesthetize the dorsal branches of the ulnar nerve: Withdraw the needle, then reinsert it dorsally and slowly infiltrate an additional 5 to 6 mL of anesthetic subcutaneously from the lateral border of the flexor carpi ulnaris tendon to the dorsal midline. 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 ulnar artery. Slide the probe transversely as needed to center the artery on the ultrasound screen. Identify the ulnar nerve medially 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 until the tip lies 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 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. 