T140. Identifying the best stimulation configuration to use for linked-quadripolar motor evoked potentials

Abstract

Neurophysiologic intraoperative monitoring (NIOM) utilizes motor evoked potentials (MEP) to assess the corticospinal tract during surgery. In most patients, 200 V or higher stimulation intensity is needed to elicit reliable MEP in the foot muscles. High stimulation intensity may result in more patient movement and adverse events such as tongue lacerations. This study is a continuation of the linked-quadripolar study that couples multiple electrodes over the scalp to assess which combination results in the most robust MEP response. MEP were obtained with different combination of anode and cathode placements. Linked double anode and cathode combinations were used. Electrodes were placed at C1, C2, C3, C4, M1, M2, M3, M4. A four-step process was used to determine the best montage. Demographic and clinical data were noted. Amplitude of both the right and left foot MEP were assessed at threshold intensity levels in order to see which electrode combination resulted in the most robust MEP. This was a retrospective study of 16 patients who underwent the 4-step linked-quadripolar study looking for the most robust foot MEP responses. On average, patients showed the highest response using a diagonal linked electrode configuration (68.75%). Seven patients (43.75%) had the highest amplitude at threshold using C1-M3/C2-M4 linked as anode/cathode. Four patients (25%) showed the highest amplitude using the C3-M1/C4-M2 linked as anode/cathode. Stimulation was lower on average from the standard bipolar montage to the linked quadripolar method (193.25–140.5 V). The linked quadripolar stimulation configuration using C1-M3/C2-M4 showed the most robust MEP response in the right foot using the lowest stimulation.