title: Etomidate dose-response on somatosensory and transcranial magnetic induced spinal motor evoked potentials in primates.
abstract: There is growing interest and need to monitor reliably both motor (MEP) and somatosensory (SEP) evoked potentials under anesthesia. On a pre-established primate model, the present study examined the effect of incremental etomidate (ET) dosages on spinal neural MEPs to transcranial magnetic stimulation (TMS) and posterior tibial rate (PTN) SEPs. Through a small thoracic T11-T12 laminotomy, an insulated double bipolar electrode was inserted epidurally in seven cynomolgus monkeys. Spinal TMS-MEPs, PTN-SEPs, and frontal EEG were tested against graded increase of ET doses. Etomidate 0.5 mg kg-1 i.v. was initially given and followed by 30 min continuous infusion of 0.01 mg kg-1 min-1, 0.018, 0.032, 0.056, 0.1, and 0.18 mg kg-1 min-1 in that order. Measurable spinal MEPs and SEPs were recorded under deep ET anesthesia (total 12.38 mg kg-1 cumulative dose over 180 min). The EEG showed marked slow wave and graded burst suppression at cumulative dose of > or = 3.14 mg kg-1. The direct (D) and subsequent initial indirect (I) waves (I1, I2, I3) were reproducible at doses < 0.18 mg kg-1 min-1 infusion. The latter I-waves (I4 and I5) showed graded loss at infusion dosage 0.056 mg kg-1 min-1. Etomidate remains an anesthetic of attractive features in neuroanesthesia. In the primate model, neural MEPs-SEPs were reproducible despite the exceedingly high dose of ET and markedly depressed EEG. Moreover, MEP-SEP can be monitored during ET burst-suppressive neuroprotective state. The study may set a model in humans for intra-operative multi-modality neurophysiologic recording under ET-based anesthesia.
authors.affiliation: Chicago Institute of Neurosurgery and Neuroresearch, IL 60614, USA.
authors.forename: R F
authors.initials: RF
authors.lastname: Ghaly
authors.forename: J J
authors.initials: JJ
authors.lastname: Lee
authors.forename: J H
authors.initials: JH
authors.lastname: Ham
authors.forename: J L
authors.initials: JL
authors.lastname: Stone
authors.forename: S
authors.initials: S
authors.lastname: George
authors.forename: P
authors.initials: P
authors.lastname: Raccforte
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004569:Electroencephalography; D005045:Etomidate / Q000494:pharmacology*; D019054:Evoked Potentials, Motor / Q000187:drug effects*; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects*; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D008251:Macaca; D008280:Magnetics; D009044:Motor Cortex / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology*; D013979:Tibial Nerve / Q000502:physiology
chemical_list: D006993:Hypnotics and Sedatives; D005045:Etomidate