Think Ultrasound to Improve Accuracy of Nerve Blocks

November 2009

By Sherry Boschert
Elsevier Global Medical News 

Emergency physicians commonly use anatomic landmarks to make an educated guess about where to inject regional anesthesia--and commonly end up frustrated when they find out 10-15 minutes later that the block failed. Up to 30% of anesthetic blocks are unsuccessful using this "landmarks" method, some studies suggest.

There's a better way, Dr. Michael B. Stone said: Use bedside ultrasound to visualize needle placement and to confirm that the anesthetic has surrounded the nerve. In a session titled "Blocks Unblinded: Ultrasound Guided Regional Anesthesia" at the Scientific Assembly of the American College of Emergency Physicians, Dr. Stone provided an introduction to the why's and how's of this technique.

Using ultrasound as a visual adjunct in nerve blocks--especially in the extremities--is not exactly new among anesthesiologists, "but emergency physicians are just catching on that this is a good way to get pain control for certain procedures," Dr. Stone, director of emergency ultrasound at the State University of New York Downstate Medical Center, Brooklyn, said in an interview.

In the traditional way of injecting regional anesthesia, the physician looks for anatomic landmarks such as muscles, bones, and the direction of tendon insertions, and uses a general understanding of where the nerves should be, based on surface anatomy, to decide where to insert the needle and inject anesthetic.

Anesthesiologists have traditionally used nerve-stimulation needles to determine anesthetic placement. They apply current through a needle tip placed in the vicinity of the target nerve, which causes the arm or leg to twitch. When anesthesia is properly injected, it stops the twitch.

The nerve-stimulation technique requires specialized equipment and takes practice, "so emergency medicine has just used landmark techniques," Dr. Stone said.

Today, many anesthesiologists have replaced or augmented nerve stimulation with ultrasound guidance of regional anesthesia injections, he added.

"You get a lot from ultrasound," he said. "Put a transducer on the patient, and you actually can visualize the nerve."

Insert the needle and watch as it approaches the nerve, place the needle adjacent to the nerve, and watch the injected local anesthetic solution surround the nerve. "You can verify that the block is going to work, so you know before you walk out of the room that this will be a good block," Dr. Stone said.

During the presentation, he explained the ultrasound-guided technique for several specific blocks, including three very common ones: femoral nerve blocks for hip fractures, forearm blocks for painful procedures of the hand, and tibial nerve blocks for painful procedures of the foot.

The foot, for example, is full of nerve endings, Dr. Stone said. "If somebody comes in with a piece of glass or foreign body in the sole of the foot, it can be a challenge to help them" without the use of a regional nerve block, he explained.

Ultrasound guidance also is useful for brachial plexus, sciatic, paravertebral, intercostal, and intra-articular blocks.

Using ultrasound for guidance lets you visualize and avoid the blood vessels and veins that run near nerves, he added. It makes some of the more advanced blocks easier and safer to do, such as injections at the top of the neck or top of the arm.

For shoulder blocks, which are useful in the treatment of a dislocated shoulder, ultrasound can reduce the risk of pneumothorax caused by puncturing the lung with the anesthetic needle. "You can see the lung and pleura and stay away from them," he said.


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