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