Are Nerve Stimulators Obsolete?

Stuart A. Grant, MB, ChB, Durham, N.C.

April, 2010

IF YOU WERE FORCED TO CHOOSE between measuring pulse or blood pressure during surgery, which one would you pick? What if you had to decide between overhead surgical lights vs. surgical headlights, or between surgical scrubs and surgical preps?

Silly questions, of course. These things work together, not competitively to help track health, illuminate surgical sites and prevent infection. In all these cases, we need both to do a good job.

That brings me to ultrasound and nerve stimulators, two technologies that provide guidance for peripheral nerve blocks.

Because I've been one of the chief proponents for ultrasound guidance over the years, I'm frequently asked whether this visualization technology makes nerve stimulation obsolete. In my view, the answer is no. I believe patient safety should be the priority, and I believe that ultrasound and nerve stimulation work together to provide the best patient outcomes. I believe it will be that way for the foreseeable future. There are several reasons why.

For anesthesia professionals who are just getting started with ultrasound, stimulation provides extremely valuable confirmation of what you think you are visualizing. Ultrasonic images can be very confusing. It's very easy to mistake a structure such as a tendon for a nerve. Attaching a stimulator to the needle and using it in the traditional way (begin with 1-1.5 mA stimulation, attenuate as you near the nerve) can help confirm that the structure you think is the nerve really is.

When practitioners become more proficient with ultrasound, stimulation is still advisable for virtually all blocks involving upper and lower limbs.

The reason: Although today's ultrasound units provide excellent images, they are still not good enough to show us whether the needle tip is in the nerve fascicle or just in the nerve's connective tissue. Knowing the tip's exact location is critical, because injecting anesthetic inside a nerve fascicle can result in temporary or permanent loss of motor nerve function and/or neuropathy.

Stimulation, I believe, can help prevent that complication. Although research is ongoing, and we only have data from animal studies, we know that stimulator current of .2mA or less will only produce a response if the needle tip is intraneural.(1) For virtually all upper and lower limb blocks, we attach a stimulator and apply a very low current. If we see stimulation we know to back the needle off before injecting.

A stimulator is virtually a sine qua non for deeper blocks, and in obese patients. Needles that are oriented vertically provide poor ultrasonic reflectance.

Is it possible to do a peripheral nerve block with ultrasound only? Of course. Is it a good idea? Not in my opinion, particularly for new practitioners of ultrasoundguided regional anesthesia. For the same reason that I like to buckle my seatbelt before releasing the parking brake, I prefer to attach my nerve stimulator before I insert a needle. I recommend the same to all my students and colleagues.

References:
1. Bigeleisen PE, Moayeri N, Groen GJ. Extraneural versus intraneural stimulation thresholds during ultrasound-guided supraclavicular block. Anesthesiology. 2009 Jun;110(6):1235-43.

Dr. Grant is a Professor of Anesthesiology at the Duke University School of Medicine, and the recipient of the 2007 Golden Apple award for excellence in teaching.


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