A radial nerve block anesthetizes the dorsum of the thenar half of the hand (from the thumb through the radial half of the ring finger), excluding the fingertips.
Radial nerve block can be done using anatomic landmarks or ultrasonographic guidance. Ultrasonographic guidance increases the likelihood of successful peripheral nerve blockade and reduces the risk of complications but requires trained personnel.
(See also Local anesthesia for laceration treatment.)
Indications
Laceration or other surgically treated lesion of the dorsum of the radial (lateral) half of the hand, including the thumb through the radial half of the ring finger, excluding the fingertips from the index finger through the radial half of the ring finger*
Ring removal
A nerve block has advantages over local anesthetic infiltration because it can cause less pain (eg, in palmar skin repair) and does not distort tissue.
* To anesthetize the entire dorsum of the hand, also do median nerve block and ulnar nerve block.
Contraindications
Absolute contraindications
History of allergy to the anesthetic agent or delivery vehicle (choose a different anesthetic)
Absence of anatomic landmarks needed to guide needle insertion (eg, due to trauma)
Relative contraindications
Infection in the path of needle insertion: Use procedural sedation or other anesthesia.
Coagulopathy*: When feasible, correct prior to procedure, or use a different means of analgesia.
* Therapeutic anticoagulation (eg, for pulmonary embolism) increases the risk of bleeding with nerve blocks, but this must be balanced against the increased risk of thrombosis (eg, stroke) if anticoagulation is reversed. Discuss any contemplated reversal with the clinician managing the patient's anticoagulation and then with the patient.
Complications
Adverse reaction to the anesthetic or delivery vehicle (eg, allergic reaction to the anesthetic [rare] or to methylparaben [a preservative])
Hematoma
Neuritis
Spread of infection, by passing the needle through an infected area
Most complications result from inaccurate needle placement.
Equipment
Nonsterile gloves
Barrier precautions as indicated (eg, face mask, safety glasses or face shield, cap and gown)
Syringe (eg, 10 mL) and needle (eg, 25 or 27 gauge, 3.5 cm long) for anesthetic injection
For ultrasonography: Ultrasound machine with high-frequency (eg, 7.5 MHz or higher) linear array probe (transducer); probe cover (eg, transparent sterile dressing, single-use probe cover); sterile, water-based lubricant, single-use packet (preferred over multi-use bottle of ultrasound gel)
* Local anesthetics are discussed in Lacerations.
Additional Considerations
Document any preexisting nerve deficit before doing a nerve block.
Stop the nerve block procedure if you are unsure where the needle is or if the patient is uncooperative. Consider sedation for patients who are unable to cooperate or remain still.
Relevant Anatomy
The radial nerve lies along the radial aspect of the wrist, just lateral (radial) to the radial artery at the proximal wrist crease.
The dorsal cutaneous branches of the nerve wrap around the radius to innervate the dorsum of the radial side of the hand.
Positioning
Position the patient with the arm resting with the palm facing up.
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.
Radial nerve block, ultrasound-guided
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.
Aftercare
Ensure hemostasis at the injection site.
Instruct patient regarding anticipated time to anesthesia resolution.
Warnings and Common Errors
To minimize the risk of needle breakage, do not bend the needle, insert it to its full depth (ie, to the hub), or attempt to change direction of the needle while it is inserted.
To help prevent nerve injury or intraneural injection, instruct patients to report paresthesias or pain during the procedure.
To help prevent intravascular injections, aspirate before injecting.
If using ultrasound, always maintain ultrasound visualization of the needle tip during insertion.
Tricks and Tips
The distribution of the radial nerve is less predictable than the distribution of other nerves of the hand and wrist, thus a generous amount of anesthesia may be needed if ultrasound guidance is not used.
Minimize the pain of injection by injecting slowly (eg, 30 to 60 seconds), warming the anesthetic solution to body temperature, and buffering the anesthetic.
