Low dose propofol as a supplement to ketamine-based anesthesia during intraoperative monitoring of motor-evoked potentials.
METHODS
Motor-evoked potentials (MEPs) were analyzed using transcranial electrical stimulation during spinal surgery in patients under ketamine-based anesthesia, with and without propofol.


OBJECTIVE
To investigate the effects of propofol on MEPs and ketamine-induced adverse effects during spinal surgery in patients under ketamine-based anesthesia.


BACKGROUND
Intraoperative monitoring of transcranial motor-evoked responses provides a method for monitoring the functional integrity of descending motor pathways. However, because these responses are sensitive to suppression by most anesthetic agents, anesthetic technique is limited during the monitoring of MEPs. Ketamine has been reported to have little effect on MEPs but may produce adverse effects such as psychedelic effect and hypertension. Recently, it has been reported that propofol may be able to inhibit ketamine-induced adverse effects.


METHODS
Intraoperative monitoring of MEPs was performed in 58 patients who underwent elective spinal surgery. Anesthesia was maintained with nitrous oxide-fentanyl-ketamine without or with low-dose (1-3 mg/kg/hr) of propofol (K group; n = 34, KP group; n = 24, respectively). Transcranial stimulation with single or paired pulses or a train of three or five pulses (interstimulus interval, 2 msec) were delivered to the scalp, and compound muscle action potentials were recorded from the left and right tibialis anterior muscles. To investigate the dose effects of propofol on MEPs, propofol was administered at an infusion rate of 6, 4, and 2 mg/kg/hr and then discontinued in 14 patients.


RESULTS
Results of MEPs were comparable between the K and KP groups. The incidence of postoperative psychedelic effect was significantly less in the KP group (14%) than in the K group (41%). Although propofol inhibited MEPs dose dependently, the use of a train of pulses for stimulation could overcome such inhibition.


CONCLUSIONS
If a train of pulses were used for transcranial stimulation, low-dose propofol can be effectivelyused as a supplement to ketamine-based anesthesia during intraoperative monitoring of myogenic MEPs. Addition of propofol significantly reduced the ketamine-induced psychedelic effects.
Kawaguchi
M
M
Departments of Anesthesiology and Neurosurgery, Nara Medical University, Nara, Japan. mkawaguc@ucsd.edu
Sakamoto
T
T
Inoue
S
S
Kakimoto
M
M
Furuya
H
H
Morimoto
T
T
Sakaki
T
T
D000293:Adolescent; D000328:Adult; D000771:Anesthesia, Intravenous / Q000379:methods*; D000778:Anesthetics, Dissociative / Q000008:administration & dosage*; D018686:Anesthetics, Intravenous / Q000008:administration & dosage*; D001921:Brain / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004359:Drug Therapy, Combination; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D007649:Ketamine / Q000008:administration & dosage*; D007866:Leg / Q000294:innervation / Q000502:physiology; D008297:Male; D016343:Monitoring, Intraoperative; D019637:Orthopedic Procedures; D015742:Propofol / Q000008:administration & dosage*; D012189:Retrospective Studies; D013118:Spinal Cord Diseases / Q000601:surgery; D013122:Spinal Diseases / Q000601:surgery
D000778:Anesthetics, Dissociative; D018686:Anesthetics, Intravenous; D007649:Ketamine; D015742:Propofol