Changing stimulation parameters for motor evoked potentials: a case study.
The purpose of this case study was to illustrate the sensitivity of intraoperative motor evoked potentials (MEPs) to stimulation parameters in the absence of any known surgical or anesthetic cause. In this cervical spine surgery, an abrupt, unexplained, unilateral loss of MEPs prompted a search among the stimulation parameter space of voltage, interpulse interval (IPI), pulse duration, and number of pulses, with a surprising result: rather than the usual dependence on voltage and IPI, the upper and lower extremity responses required mutually exclusive combinations of pulse duration and number of pulses (nine pulses, 350 V, 2.5-millisecond IPI, 200 microseconds and four pulses, 220 V, 2.5-millisecond IPI, 500 microseconds, respectively). Parameters far from these sets abolished the responses. The patient's neurologic status was preserved. The authors conclude that exploring alternative stimulation parameters can help to reduce the MEP false-alarm rate by restoring responses without unwarranted changes in the surgical plan.
Noss
Roger S
RS
Department of Neurological Surgery, University of California, San Francisco, California 94143-0220, USA. roger.noss@ucsfmedctr.org
Ames
Christopher
C
D000328:Adult; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology / Q000528:radiation effects*; D005260:Female; D006801:Humans; D016343:Monitoring, Intraoperative; D009044:Motor Cortex / Q000503:physiopathology / Q000528:radiation effects*; D019635:Neurosurgical Procedures; D013116:Spinal Cord / Q000601:surgery; D013997:Time Factors