Three-D ultrasound provides guidance for nerve blocks

Three-D ultrasound designed for cardiac imaging may be just what interventionalists need to improve the administration of nerve blocks, according to researchers at the Mayo Clinic in Jacksonville, FL.

Anesthesiologists Neil Feinglass and Steven Clendenen have adapted a Philips iU22 echocardiography system and cardiac probes to visualize nerves so as to better administer local anesthesia. The 3D images help guide needles to nerve endings, such as those exiting the cervical spine.

Nerve blocks can reduce the time needed for interventions, helping such procedures run more efficiently and sparing patients the effects of general anesthesia, Clendenen said. But nerve blocks are difficult to administer, even with 2D ultrasound.

"The problem with 2D is finding the tip of the needle," Clendenen said. "You have to manipulate the probe and jiggle the needle to find it. With 3D ultrasound, you manipulate the image."

Clendenen has discussed with Philips executives how its technology might be tailored for anesthesiology. One idea is to develop a system with presets optimized for nerve imaging. This would include removing echo features. Another idea is to boost the frequency from 7 MHz to 9 MHz to improve resolution in the near field and to expand the width of the probe for more coverage.

In the meantime, Clendenen and Feinglass are making do with off-the-shelf equipment. They have had their best results using an x7-2 Matrix array, which Philips designed to image infant hearts. The resolution with this probe is good enough to actually see the nerve roots, Clendenen said, compared with 2D imaging, which produces little more than longitudinal dots indicating the presence of nerves.

The Mayo physicians have used the 3D technique to place blocks on nerves in the neck, under arms, below collarbones, and in the back upper portion of legs. Such regional blocks exert less stress on patients' hearts. This promotes recovery and improved rehabilitation, Clendenen said. Through detailed guidance, a miniature catheter can be placed alongside the nerves, allowing for at-home administration of anesthetic.

"We can send people home the day of or day after surgery instead of keeping them in the hospital with a morphine infusion," he said. "It is cutting-edge technology."