title: Some effects of isoflurane on I waves of the motor evoked potential.
abstract: We have investigated the effects of isoflurane anaesthesia on the motor evoked potential recorded in the extradural space during corrective spinal surgery in 15 patients. Isoflurane was added to a nitrous oxide in oxygen mixture supplemented with fentanyl and a neuromuscular blocking agent. Isoflurane was administered to achieve end-tidal concentrations of 2%, 1% and 0% in all patients, and also of 1.5% and 0.5% in nine patients. Transcranial electrical stimulation of the motor cortex was used to elicit descending volleys in corticospinal axons (the motor evoked potential). With stimuli of 450-750 V and no isoflurane, multiple I waves were always seen following the D wave. In all patients the number of I waves decreased and individual I waves became smaller in amplitude the greater the isoflurane concentration, but there were only minor changes in the D wave. The greatest depressant effect on I waves occurred at an end-tidal concentration of 0.5%. Given that I waves are an index of synaptic transmission, anaesthetic-induced changes in I waves may provide a useful model for the neuronal events underlying anaesthesia-induced unconsciousness.
authors.affiliation: Department of Clinical Neurophysiology, Prince Henry Hospital, Little Bay, N.S.W., Australia.
authors.forename: R G
authors.initials: RG
authors.lastname: Hicks
authors.forename: I J
authors.initials: IJ
authors.lastname: Woodforth
authors.forename: M R
authors.initials: MR
authors.lastname: Crawford
authors.forename: J P
authors.initials: JP
authors.lastname: Stephen
authors.forename: D J
authors.initials: DJ
authors.lastname: Burke
mesh_terms: D000293:Adolescent; D001369:Axons / Q000502:physiology; D002648:Child; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects; D005260:Female; D006801:Humans; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D009044:Motor Cortex / Q000187:drug effects*; D013116:Spinal Cord / Q000502:physiology
chemical_list: D007530:Isoflurane