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Use of Sequential Electrical Nerve Stimuli (SENS) for Location of the Sciatic Nerve and Lumbar Plexus
  1. William F. Urmey, M.D. and
  2. Paolo Grossi, M.D.
  1. Department of Anesthesiology, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, NY
  2. Department of Anesthesiology, Istituto Policlinico San Donato, Universita degli Stidi di Milano, Milan, Italy.
  1. Reprint requests: William F. Urmey, M.D., Department of Anesthesiology, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021. E-mail: urmeyw{at}


Background and Objectives: Conventional electrical stimulation has been done by continuous adjustment of current amplitude at a single, set pulse duration (conventionally, 0.1 ms). This study evaluated a novel technique for nerve location by utilization of a peripheral-nerve stimulator (PNS) programmed to deliver sequential electrical nerve stimuli (SENS). A repeating series of alternating sequential pulses of 0.1, 0.3, and 1.0 ms at 1/3-second period intervals between pulses were generated so that at a greater distance from the nerve, only higher-duration pulses would stimulate the targeted nerve and result in 1 or 2 motor responses (MR) per second. Three MR per second at 0.5 mA or less signified the conventional endpoint for nerve location (≤0.5 mA, 0.1 ms) because that value indicated that the 0.1-ms pulse was effective. The conventional 0.1-ms pulse served as a built-in control to which the SENS was compared.

Methods: Sixteen sciatic/psoas blocks were performed on 8 patients. Nerve location was by SENS, with an 80-mm block needle. Needle advance began at 1.0 mA until MR. If 1 or 2 MR/s occurred, the needle was advanced until 3 MR/s were obtained. When 3 MR/s occurred at 0.5 mA or less, needle position was fixed (final position), and mA further decreased until MR disappeared. Two digital video cameras separately recorded needle depth and MR for analysis. Final needle position was designated as zero, and distance was calculated relative to it.

Results: In 12 of 16 of the performed blocks, SENS resulted in advanced notification (1 or 2 MR/s), which yielded additional visual feedback compared with control before final nerve location and, thus, increased range. In 15 of 16 blocks, MR did not disappear, once elicited, through final needle location.

Conclusions: SENS resulted in increased sensitivity without compromising specificity of nerve location.

  • Nerve stimulation
  • Peripheral nerve
  • Electrical stimulation
  • Nerve location

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  • This work was presented at the 31st Annual ASRA Meeting, April 2006, Palm Springs, California.

    All work was funded by the investigators and the Istituto Policlinico San Donato.