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Effects of common agents on the EEG, cortical SSEPs, and muscle MEPs

Effects of common agents on the EEG, cortical SSEPs, and muscle MEPs
Agent EEG/ECoG[1] SSEP amplitude MEP amplitude Comments
Isoflurane With increasing concentrations, initial increased frequency of the frontal EEG during light anesthesia, decreased frequency and increased amplitude as anesthesia deepens, until frequency and amplitude decrease to burst suppression and eventually to electrical silence Decrease Decrease SSEP usually recorded at <1 MAC, MEP <0.5 MAC
Sevoflurane Similar to isoflurane; seizures possible with mask induction and hyperventilation Decrease Decrease Similar to isoflurane
Desflurane Similar to isoflurane Decrease Decrease Similar to isoflurane
N2O Decrease in amplitude of some frequencies but activation of some other frequency ranges Decrease Decrease Similar to isoflurane, synergistic when combined with halogenated agents
Propofol With increasing doses, increase in frequency of frontal EEG during light anesthesia, slower frequency and increased amplitude as dose is increased, progressing to burst suppression and eventually electrical silence Decrease Decrease SSEP and MEP usually recorded at anesthetic doses but MEP may be lost at high doses
Barbiturates Similar to propofol; methohexital activates epileptic spike activity during ECoG Decrease Decrease Similar to propofol; limited experience with MEP
Opioids Increase amplitude, decrease frequency; no EEG suppression at high doses; spike activation with boluses Minimal Minimal SSEP and MEP usually recorded even at high doses
Etomidate Decreases amplitude and frequency; electrical silence at high dose; low doses enhance epileptic activity Increase at low doses – decrease at higher doses Increase at low doses – decrease at higher doses Enhancement of SSEP and MEP seen at low doses, depression at very high doses
Ketamine High amplitude slow waves; can induce seizures in patients with epilepsy Minimal, increase at low doses Minimal, increase at low doses Enhancement SSEP and MEP seen at low doses
Benzodiazepines Decreases amplitude and frequency; reduces interictal epileptiform activities Minimal at low doses Minimal at low doses, prolonged decrease at higher doses SSEP and MEP usually recorded with small doses for amnesia
Dexmedetomidine Minimal – mimics sleep Minimal Minimal – decrease at higher doses SSEP and MEP usually recorded at low doses but MEP lost at higher doses
Lidocaine Low dose – anti seizure; high dose – seizures Minimal Minimal Can be used as intravenous supplement in SSEP and MEP
Anesthetic effects may be significantly greater in young children (immature pathways) and adults with significant neural dysfunction. Latency increases generally occur as amplitude is decreased. This table should be used in conjunction with UpToDate content on neuromonitoring during surgery and anesthesia.
ECoG: electrocorticography; EEG: electroencephalography; MAC: minimum alveolar concentration; MEP: motor evoked potentials; N2O: nitrous oxide; SSEP: somatosensory evoked potentials.
Reference:
  1. Galloway SG, Sloan TB. Epilepsy and Seizures: OR and ICU applications of EEG. In: Monitoring the Nervous System for Anesthesiologists and Other Health Care Professionals, 2nd ed, Koht A, Sloan TB, Toleikis JR (Eds), Springer 2017.

Adapted from: Shils JL, Sloan TB. Intraoperative neuromonitoring. Int Anesthesiol Clin 2015; 53:53.

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