Effect of low-dose ketamine on voltage requirement for transcranial electrical motor evoked potentials in children.
METHODS
Randomized controlled trial. OBJECTIVE.: To determine the effect of low-dose ketamine on the voltage needed to elicit maximal amplitude of the motor-evoked response to transcranial electrical stimulation during propofol/remifentanil anesthesia in children undergoing scoliosis surgery.


BACKGROUND
Motor-evoked potentials (MEPs) are increasingly used to assess the integrity of motor pathways during surgery. Whereas most general anesthetics depress MEP amplitude, the effect of ketamine has been variable, ranging from little or no reduction to an increase in amplitude, suggesting that ketamine may be useful as an agent to facilitate MEP monitoring. We tested the hypothesis that low-dose ketamine would reduce the voltage required to elicit maximal amplitude of the motor-evoked response to transcranial electrical stimulation during propofol/remifentanil anesthesia.


METHODS
Thirty-four patients 12 to 16 years of age undergoing posterior instrumentation for correction of idiopathic scoliosis were randomly assigned to receive low-dose ketamine (0.5 mg/kg bolus, followed by 4 microg/kg/min infusion) or an equal volume of saline. Anesthesia was maintained using a mixture of 30% oxygen in air, continuous infusion of propofol at a rate of 100 to 150 microg/kg per min, and continuous infusion of remifentanil. Myogenic motor-evoked responses to transcranial electrical stimulation of the motor cortex were recorded. The minimum voltage required to elicit maximal amplitude of the MEP response was determined. Voltage requirements were compared using the Mann-Whitney U rank sum test. P < 0.05 was considered statistically significant.


RESULTS
No significant difference was found in the minimal voltage needed to elicit maximum amplitude of the MEP response. Median (range) voltage requirements in the ketamine and control groups were 227 V (range, 160-350 V) and 215 V (range, 150-300 V), respectively.


CONCLUSIONS
Addition of low-dose ketamine to propofol/remifentanil anesthesia does not significantly reduce the voltage needed to elicit maximum amplitude of the motor-evoked response to transcranial electrical stimulation.
Zaarour
Christian
C
Department of Anesthesia, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada.
Engelhardt
Thomas
T
Strantzas
Samuel
S
Pehora
Carolyne
C
Lewis
Stephen
S
Crawford
Mark W
MW
D000293:Adolescent; D000778:Anesthetics, Dissociative; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D002648:Child; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004525:Efferent Pathways / Q000187:drug effects / Q000502:physiology; D019054:Evoked Potentials, Motor / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006801:Humans; D007431:Intraoperative Complications / Q000517:prevention & control*; D007649:Ketamine; D008297:Male; D016343:Monitoring, Intraoperative / Q000379:methods*; D010880:Piperidines / Q000494:pharmacology; D011237:Predictive Value of Tests; D015742:Propofol / Q000494:pharmacology; D011712:Pyramidal Tracts / Q000187:drug effects / Q000502:physiology; D000077208:Remifentanil; D012600:Scoliosis / Q000601:surgery; D012680:Sensitivity and Specificity; D013119:Spinal Cord Injuries / Q000503:physiopathology / Q000517:prevention & control*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*
D000778:Anesthetics, Dissociative; D018686:Anesthetics, Intravenous; D010880:Piperidines; D007649:Ketamine; D000077208:Remifentanil; D015742:Propofol