EEG Monitoring in Anesthesia

Overview

This lecture by Dr. Patrick Purdon focused on using EEG (electroencephalogram) patterns to monitor and personalize anesthesia, discussing the neurophysiology underlying different anesthetic drugs, age effects, and clinical implications, supported by studies and real-life case examples.

Introduction to EEG Monitoring in Anesthesia

• EEG reflects real-time brain states during anesthesia, enabling individualized dosing.
• Traditional monitoring relies on cardiovascular signals and pharmacokinetic models, but these often mismatch with individual patient responses.
• EEG allows for personalized anesthesia by directly observing the brain’s response to anesthetic drugs.

Typical EEG Patterns under Anesthesia

• EEG patterns change with increasing drug dose: initial beta/alpha oscillations, then slow oscillations, and finally burst suppression at high doses.
• Burst suppression (alternating flat and active periods in EEG) corresponds to deep unconsciousness or coma and is beyond necessary anesthesia depth.
• Spectral analysis of EEG reveals specific oscillatory patterns linked to anesthetic depth.

Mechanisms and Drug-Specific EEG Patterns

• Anesthetics like propofol and sevoflurane amplify GABAergic (inhibitory) signaling, generating strong fronto-thalamocortical alpha and slow oscillations.
• Dexmedetomidine, an alpha-2 agonist, creates spindle-like EEG patterns resembling non-REM sleep and allows arousable sedation.
• Ketamine (NMDA antagonist) leads to higher-frequency (≈30 Hz) oscillations, sometimes causing dissociative states.

Clinical Applications and Case Studies

• EEG monitoring reveals when patients are over- or under-dosed, even if standard clinical signs seem normal.
• Elderly and pediatric patients show reduced EEG signal amplitude, potentially leading to misinterpretation by existing "one-number" depth monitors.
• Proper EEG interpretation helps avoid burst suppression, which is linked to post-operative delirium and cognitive complications.
• Multi-modal anesthesia using combinations of drugs (e.g., propofol, ketamine, dexmedetomidine) enables lower doses and tailored sedation.

Age and Developmental Effects

• EEG oscillation amplitude and pattern change with age—signals are smaller in the very young and elderly, but the underlying oscillatory structure remains.
• Standard monitors may misguide dosing in these populations, but direct EEG visualization corrects for these differences.

Key Terms & Definitions

• EEG (Electroencephalogram) — A recording of brain electrical activity from the scalp.
• Burst Suppression — Alternating periods of silence and activity in EEG, indicating deep anesthesia or coma.
• Alpha Oscillations — EEG frequencies 8-12 Hz, seen during anesthesia in the frontal cortex.
• Slow Oscillations — Large, <1 Hz waves, indicating profound suppression of cortical activity.
• Spectral Analysis — Technique to examine the frequency content of EEG signals.
• Pharmacokinetics/Dynamics — Drug movement through the body and its effects.

Action Items / Next Steps

• Review course modules on EEG/drug combinations (see online program, module 2).
• Prepare for further discussion on age/developmental effects and critical periods in upcoming lectures.
• For clinicians: Consider integrating real-time EEG monitoring for all anesthesia patients to individualize care and minimize complications.