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Anesthetic Drugs and the Electroencephalogram

Drug	Effect on EEG Frequency	Effect in EEG Amplitude	Burst Suppression
Isoflurane			Yes, >1.5 MAC
Subanesthetic	Loss of α, ↑ frontal β	↓
Anesthetic	Frontal 4- to 8-Hz activity	↑
Increasing dose >1.5 MAC	Diffuse θ and δ → burst suppression → silence	↑ → 0
Enflurane			Yes, >1.5 MAC
Subanesthetic	Loss of α, ↑ frontal β	↓
Anesthetic	Frontal 7- to 12-Hz activity	↑
Increasing dose >1.5 MAC	Spikes/spike and slow waves → Burst suppression; hypocapnia → Seizures	↑↑
Halothane			Not seen in clinically useful dose range
Low dose	↑ Frontal 10- to 20-Hz activity	↓
Moderate dose	Frontal 10- to 15-Hz activity	↑
Increasing dose >1.5 MAC	Diffuse θ, slowing with increasing dose	↑
Desflurane	Similar to equi-MAC dose of isoflurane	Similar to equi-MAC dose of isoflurane	Yes, >1.2 MAC
Nitrous oxide (alone)	Frontal fast oscillatory activity (>30 Hz)	↑, especially with inspired concentration >50%	No
Barbiturates			Yes, with high doses
Low dose	Fast frontal β activity	Slight ↑
Moderate dose	Frontal α frequency spindles	↑
Increasing high dose	Diffuse δ → burst suppression → silence	↑↑↑ → 0
Etomidate			Yes, with high doses
Low dose	Fast frontal β activity	↓
Moderate dose	Frontal α frequency	↑
Increasing high dose	Diffuse δ → burst suppression → silence	↑↑ → 0
Propofol			Yes, with high doses
Low dose	Loss of α, ↑ frontal β	↓
Moderate dose	Frontal δ, waxing-waning α	↑
Increasing high dose	Diffuse δ → burst suppression → silence	↑↑ → 0
Ketamine			No
Low dose	Loss of α, ↑ variability	↑ ↓
Moderate dose	Frontal rhythmic θ	↑
High dose	Polymorphic δ, some β	↑↑ (β is low amplitude)
Benzodiazepines			No
Low dose	Loss of α, increased frontal β activity	↓
High dose	Frontally dominant δ and θ	↑
Opiates			No
Low dose	Loss of β, α slows	↔ ↑
Moderate dose	Diffuse θ, some δ	↑
High dose	δ, often synchronized	↑↑

α = alpha (8-13 Hz) frequency; β = beta (>13 Hz) frequency; δ = delta (<4 Hz) frequency; MAC = minimum alveolar concentration; θ = theta (4-7 Hz) frequency.
Note: Arrows indictate direction of change; number of arrows indicates the magnitude of change.

Adapted from Black S, Mahla ME, Cucchiara RF. Neurologic Monitoring. In RD Miller. (ed). Anesthesia. New York: Churchill Livingston, 1994:1323.

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