Forarm Nerve Blocks

26

ACEP

PRACTICE TRENDS

NEWS

•

MARCH 2007

TRICKS OF THE TRADE

Forearm Ultrasound-Guid.ed Nerve (FUIN) Blocks

BY MICHELLE LIN,

M.D . , AND

COURTNEY WASHINGTON

and injuries represent 5%-10% of

ED visits throughout the United

States. Patients often need to under­

go painful hand procedures, such as sutur­

ing, debridement, or wound exploration.

It can be difficult to provide adequate

pain control for these patients. Further, lo­

cal anesthesia can cause further damage to

the area. Forearm Ultrasound-Guided

Nerve (FUN) blocks can help identify the

radial, ulnar, and median nerves in the

forearm to assist in regional blocks. Nerve

bundles on ultrasound appear hyperechoic

(white), while blood vessels appear hy­

poechoic (dark).

.. Trick of the Trade: Radial Nerve.

Place the vascular ultrasound probe trans­

versely to identify the round-shaped radi­

al artery in cross-section along the volar

wrist. While keeping the artery in the

center of the visual field, move the probe

proximally until the radial nerve can be vi­

sualized. The round-shaped hyperechoic

nerve runs parallel and lateral, or radial, to

the artery. Once identified, anesthetic can

H

be injected laterally and medially to the nerve. Be aware that the nerve is best vi­ sualized in the midforearm. Anesthesia should be instilled at the forearm level un­ der direct ultrasonographic guidance. .. Trick of the Trade: Ulnar Nerve. Iden­ tify the ulnar nerve Similarly to the radial nerve (see first photo). Be aware that the ulnar nerve is located medial, or ulnar, to the ulnar artery. iii- Trick of the Trade: Median Nerve. Be­ cause the median nerve does not have a corresponding artery, the probe should be placed transversely on the volar surface of the wrist between the ulnar and radial artery. As the probe is moved proximally, the median nerve will be visualized with­ in the flexor digitorum muscle bundles. In­ ject the anesthetic at the forearm level un­ der direct ultrasonographic guidance. Although regional hand blocks are usu­ ally performed at the level of the wrist us­ ing external landmarks, the FUN block al­ lows you to more accurately administer anesthetics. The ideal place to inject the anesthetic is always where the nerve can be best vi­ sualized on ultrasound. Do not be alarmed

if that means injecting at the level of the proximal forearm. We wish to thank Dr. Otto Liebmann at Highland Hospital, Alameda County Med­ ical Center, Oakland, Calif., for this con­ tribution. Adclitional images can be viewed in the November 2006 issue of the Annals of Emergency Medicine publication by Dr. Liebmann et al.I •

References I. Liebmann 0., Price D., Mills c., et al. Feasibility of forearm ultrasonography­ Image of the hypoechoic ulnar artery (A) guided nerve blocks of the radial, ulnar, and adjacent hyperechoic ulnar nerve (N). and median nerves for hand procedures in the emergency department. Ann. Emerg. Med. 2006;48:558-62.

DR. LIN practices emergency medicine and is the medical edltCation director at San Francisco General Hospital. She is also an assistant clinical professor of medicine at the University of California, San Francisco. Contact Dr. Lin at mlin@ sfghed.ucsfedu with comments or suggestions for other "tricks of the trade." Ms. WASHINGTON is a senior medical student at Meharry Medical College, Nashville, Tenn.

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Photo shows proper FUN block technique of the median nerve in the right forearm.