title: The use of ketamine or etomidate to supplement sufentanil/N2O anesthesia does not disrupt monitoring of myogenic transcranial motor evoked responses.
abstract: Intraoperative monitoring of myogenic transcranial motor evoked responses (tc-MERs) requires an anesthetic technique that minimally depresses response amplitudes. Acceptable results have been obtained during opioid/N2O anesthesia, provided that the concentration of N2O does not exceed 50%. However, this technique may necessitate supplementation with additional agents to achieve adequate depth of anesthesia. Etomidate and ketamine have been reported anecdotally or in nonsurgical situations to produce little tc-MER depression. We investigated the effects on tc-MER amplitude and latency of supplementation of a sufentanil/N2O anesthetic with etomidate or ketamine in patients undergoing spinal instrumentation. Anesthesia was induced with etomidate 0.3 mg/kg and sufentanil 1.5 mg/kg and maintained with sufentanil 0.5 mg/kg/h and N2O 50%. Muscle relaxation was kept at 25% of control. Paired transcranial electrical stimulation was performed. Each patient randomly received either ketamine (0.5 mg/kg) or etomidate (0.1 mg/kg) as a single bolus intravenously, during stable surgical conditions. Triplicate tc-MERs were recorded from the tibialis anterior muscles before and 2, 5, 10, and 15 min after drug administration. Administration of ketamine did not significantly change tc-MER amplitudes, whereas etomidate resulted in a transient amplitude depression to 72% of control (p < 0.05) at 2 min after injection. Latency remained unchanged with both drugs. In conclusion, the data suggest that both ketamine (0.5 mg/kg) and etomidate (0.1 mg/kg) can be used to supplement sufentanil/N2O anesthetic without disrupting tc-MER monitoring.
authors.affiliation: Department of Anesthesiology, University of Amsterdam, The Netherlands.
authors.forename: L H
authors.initials: LH
authors.lastname: Ubags
authors.forename: C J
authors.initials: CJ
authors.lastname: Kalkman
authors.forename: H D
authors.initials: HD
authors.lastname: Been
authors.forename: M
authors.initials: M
authors.lastname: Porsius
authors.forename: J C
authors.initials: JC
authors.lastname: Drummond
mesh_terms: D000293:Adolescent; D000328:Adult; D000768:Anesthesia, General; D000771:Anesthesia, Intravenous; D018681:Anesthetics, General; D018686:Anesthetics, Intravenous; D002648:Child; D004558:Electric Stimulation; D005045:Etomidate; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D006801:Humans; D007649:Ketamine; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D009609:Nitrous Oxide; D017409:Sufentanil
chemical_list: D018681:Anesthetics, General; D018686:Anesthetics, Intravenous; D007649:Ketamine; D017409:Sufentanil; D009609:Nitrous Oxide; D005045:Etomidate