July 16, 2007 Mayo Clinic physicians have adapted real-time 3-D ultrasound imaging devices -- including one designed to look at an infant's heart -- so that they can watch as they use a needle filled with anesthetic to numb individual nerves located inches under the skin. In this way, they can quickly block nerve function in selected areas of the body prior to surgery, an advance that may spare patients from use of general anesthesia and sends them home faster and with less need for pain medication.
Mayo anesthesiologists have demonstrated the benefits of real-time 3-D ultrasound in nerve blockade in more than 150 surgeries of varied types. Their presentations at scientific meetings and publications in peer-reviewed journals have informed other physicians worldwide into how this next-era ultrasound imaging technology may assist in peripheral nerve block placement -- the technique of disabling targeted nerves so that a patient doesn't feel pain from surgery.
For example, their latest case study, reported in the July issue of Anesthesia & Analgesia, describes how they used 3-D ultrasound to find the sciatic nerve behind the thigh of a woman who needed major reconstructive surgery on her foot. Using the imaging technique to help physicians place a catheter filled with local anesthetic next to the nerve, they numbed it to block pain signals from being transmitted to the brain of the patient, who was sedated.
When the brain doesn't know surgery is under way because the nerve is inactivated, it doesn't mount the kind of systematic pain response that keeps patients medicated and in their beds, says anesthesiologist Steven Clendenen, M.D., who helped develop use of the technique with Neil Feinglass, M.D., and other anesthesiologists at Mayo Clinic in Jacksonville.
"Now we can find the nerve we want in real-time 3-D, guide our needle right next to it, then watch as anesthesia is released and surrounds the nerve, inactivating it," Dr. Feinglass says. "No one thought peripheral regional blocks could be done in real-time 3-D, and we believe we are the first in the world to really do it."
Most people are familiar with traditional 3-D ultrasound probes that can see a growing fetus and an adult's beating adult heart using waves that penetrate deep within body tissue and reflect back to form an image. But these devices cannot be used to picture nerves, because nerves are often too close to the surface of the skin and too shallow for the sound waves generated to form an image.
Dr. Feinglass, who specializes in cardiac anesthesiology, and Dr. Clendenen, an expert on regional pain blocks, thought of using smaller ultrasonic probes to image nerves. "We thought nerves could be very ultrasound friendly because they run in a linear plane and are wrapped in a sheath of fat, so they easily reflect back ultrasound waves," says Dr. Clendenen.
They tested two different Philips transducers (the hand held probes held by physicians against the body which emit the ultrasound waves) known as the x3-1 and x7-2 Matrix array tranducers. The x7-2 Matrix array had been recently designed to image the tiny hearts of infants.
Both provide sharp resolutions even at shallow depths, Dr. Clendenen says. Still, it took a lot of effort to master a technique for using these probes to see single nerves," he says. "They weren't designed for it."
The physicians have used this technique to place blocks on nerves in the neck, under arms, below collarbones, and in the backside upper portion of legs. "Our small group of anesthesiologists works well together in developing technology and bringing it quickly to the bedside," Dr. Feinglass says. "We find that when regional nerve blocks are used, patients have less stress on their hearts, better recovery and improved rehabilitation."
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