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

Agent	EEG/ECoG¹	SSEP amplitude	MEP amplitude	Comments
Isoflurane	Increases frequency and amplitude at lower doses; decreases with higher doses to eventual burst suppression and 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	Less amplitude and frequency change at higher doses compared to isoflurane; effect varies with other agents used	Decrease	Decrease	Similar to isoflurane, synergistic when combined with halogenated agents
Propofol	Decreases amplitude and frequency; electrical silence at higher doses	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.

EEG: electroencephalography; ECoG: electrocorticography; SSEP: somatosensory evoked potentials; MEP: motor evoked potentials; MAC: minimum alveolar concentration; N₂O: nitrous oxide.

Reference:

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