What are the duration and intensity of somatosensory evoked potentials (SEPs)?

Updated: Feb 26, 2019
  • Author: Sombat Muengtaweepongsa, MD, MSc; Chief Editor: Selim R Benbadis, MD  more...
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Answer

Answer

The selected nerves are stimulated with monophasic square pulses, 100-300 microseconds in duration. Stimuli are delivered by using either a constant voltage or a constant current stimulator.

The contact impedances of the stimulating electrodes should be kept low for the following reasons:

  • To minimize patient discomfort

  • For more effective nerve stimulation, if a constant voltage stimulator is used

  • To minimize the electrical stimulus artifacts in the recorded data

In the clinical setting, the stimulus intensity is set high enough to produce a consistent muscle twitch, which usually is tolerable to the patient. Because the patient is anesthetized during intraoperative SEP monitoring, higher stimulus intensities can be used and are advisable to provide a safety margin in case the efficacy of nerve stimulation decreases during surgery. Factors that can decrease the efficacy of nerve stimulation include edema of the limb, partial short-circuiting of the stimulating current by fluids, and ischemia of the peripheral nerve. [1]


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