3:35 Can currently used electrical stimulators reliably obtain transcranial motor-evoked potentials?

Abstract

Purpose of study: Transcranial motor-evoked potentials (TCMEPs) are increasingly being used in conjunction with somatosensory evoked potentials (SSEPs) during spinal surgery to more comprehensively monitor spinal cord function. The use of multipulse stimulation technique allows responses to be elicited with trains of lower current pulses [1]. Our initial experience suggests that electrical stimulators as currently approved by the Food and Drug Administration (FDA) are inadequate for eliciting lower-limb TCMEPs in a clinically reliable manner.Methods used: We reviewed our first 41 consecutive spinal surgical cases over a 14-month period during which both TCMEPs and SSEPs were monitored. TCMEPs were elicited by passing up to seven monophasic anodal or cathodal electrical pulses (as high as 200 mA, 500 usec duration, 300 Hz) through subdermal needle electrodes placed 2 cm anterior to C3 and C4. Pairs of subdermal recording needles were placed over the adductor magnus, vastus lateralis, tibialis anterior, gastrocnemius and thenar muscles. Primarily an intravenous anesthetic technique was used. Short-acting neuromuscular blockage was used during induction and spinal exposure.of findings: TCMEPs were successfully recorded from both lower limbs in only 66% of cases (27 of 41). In contrast, tibial nerve SSEPs were successfully recorded in 98% of cases (40 of 41). A subgroup of patients premedicated with Clonidine increased the success rate of obtaining TCMEPs from 56% (14 of 25 cases without Clonidine) to 80% (13 of 16 cases with Clonidine).Relationship between findings and existing knowledge: In this study, using current FDA-approved electrical stimulators, TCMEPs could not be reliably elicited for monitoring spinal cord function.Overall significance of findings: We think that electrical stimulators capable of delivering greater currents in combination with refinement of anesthetic technique may be necessary to elicit TCMEPs in a more reliable fashion.Disclosures: Device or drug: transcranial motor-evoked potentials. Status: investigational.Conflict of interest: No conflicts.