Use of sequential electrical nerve stimuli (SENS) for location of the sciatic nerve and lumbar plexus.
OBJECTIVE
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.
Urmey
William F
WF
Department of Anesthesiology, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, NY 10021, USA. urmeyw@hss.edu
Grossi
Paolo
P
D000328:Adult; D000368:Aged; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008160:Lumbosacral Plexus / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009407:Nerve Block; D012584:Sciatic Nerve / Q000502:physiology*