Making processed EEG work in perioperative practice

Summary

Join Dr. Alice J Humphreys, Consultant Anaesthetist, in her session about implementing processed EEG in perioperative practice. She will explain the background and theory of processed EEG, including its engineering and usage in common monitors. Useful topics include the dissection of a Bispectral Index, an understanding of depth of anaesthesia, and consciousness. She'll discuss the BIS calculation and reveal the directional delay phenomenon in processed EEG. Attendees will learn how to leverage various monitors like BIS, Narcotrend, E-entropy, and Sedline in a perioperative setting and understand the interpretive power of EEG waveforms and density spectral arrays. This session is a unique opportunity to explore the controversies and benefits of EEG in medical practice.

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Description

Join our webinar, "Making Processed EEG Work in Perioperative Practice," to explore the latest advancements in EEG technology for perioperative care. Learn practical applications, interpretation techniques, and benefits for patient outcomes. Ideal for anesthesiologists and perioperative professionals seeking to enhance their clinical practice with cutting-edge EEG insights.

None of the planners for this educational activity have relevant financial relationship(s) to disclose with ineligible companies whose primary business is producing, marketing, selling, re-selling, or distributing healthcare products used by or on patients.

Dr Alice Jamie Humphreys, faculty for this educational event, has no relevant financial relationship(s) with ineligible companies to disclose.

Learning objectives

By the end of this teaching session, learners will understand the theory and background of using the processed EEG (pEEG) in perioperative practice.
Learners will be able to explain the function of commonly used monitors in anaesthesiology, such as the Bispectral Index (BIS), Narcotrend, E-Entropy, and Sedline.
Learners will be knowledgeable about the engineering breakdown of BIS and understand how to interpret the BIS values and depth of anaesthesia in clinical settings.
Learners will gain a practical understanding of the implementation and use of pEEG techniques for cranial surgery, including placing electrodes and interpreting waveform & density spectral arrays.
By the end of the session, learners should comprehend the limitations and potential issues with using the BIS monitor, including its controversies, cost implications, and irrationals associated with its calculation.

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Making processed EEG work in perioperative practice Dr. Alice J Humphreys FRCA Consuthant Anaesthetist MedAll education event, 15 August 2024 I have no financial conflicts of interest to declare.  The views expressed herein are those of myself and the authors of papers cited, and are not necessarily representative of those of His Majesty’s Government, University Hospitals Plymouth NHS Trust or any other Disclaimer body.  This presentation is released under the terms of the Creative Commons BY-NC-SA license, with the exception of the stock and referenced images used here where the rights are retained by the original author or other copyright holder.Making processed EEG work in cranial surgery  pEEG background and theory  Engineering breakdown of BIS  Use of common monitors  EEG waveform & density spectral array  Electrode placement optionsAAGBI/SIV A TIV A guidelines 2018 16 8. Anaesthetists should be familiar with the principles, interpretation and limitations of processed EEG trace and electromyography activity is likely to improve the clinical utility of the monitoring. when a neuromuscular blocking drug is used with TIVA.ed 32 Available DoA monitors  Bispectral Index (BIS) – Aspect/Covidien/Medtronic  Licensed modules from Mennen Medical, Philips and Dräger  Narcotrend - Gwenagen/Pharmed  E-Entropy - GE Healthcare  Sedline – Masimo  Raw EEG – multiple manufacturersBispectral Index Bispectral Index  Launched in 1994 by Aspect Medical Systems, Inc.  Subsequently acquired by Covidien, in turn bought by Medtronic  Takes the incoming EEG waveform, deconstructs it via Fourier analysis then analyses it using proprietary algorithm that produces a dimensionless number between 0 and 100  Recommended for use in general anaesthesia in NICE diagnostics guidance DG6 32 19 BIS values and depth of anaesthesia BIS value Corresponding level of sedation Descriptors 100 Awake state; patient able to respond appropriately to verbal Anxiolysis stimulation (baseline state before sedation) 80 Patient able to respond to loud verbal, limited tactile Moderate sedation stimulation, such as mild prodding/shaking 60 Low probability of explicit recall; patient unresponsive to verbal Deep sedation stimulation 40 Patient unresponsive to verbal stimulation, less responsive to Deep hypnotic state physical stimulation 20 Minimal responsiveness Drug-induced coma; burst-suppression EEG pattern 0 No responsiveness mediated by brain function; spinal reflexes Isoelectric or completely suppressed EEG may be present What is consciousness?  Consciousness → unconsciousness → anaesthesia  Viewpoints include  One’s “inner life”; the world of introspection, of private thought, imagination and volition  Today, it often includes any kind of cognition, experience, feeling or perception  It may be awareness, awareness of awareness, or self- awareness, either continuously changing or not“ Cogito ergo sum ” René Descartes Discourse on the Method, 1637Consciousness on EEG Alpha, beta and gamma activityREM sleep on EEG Alpha, beta and gamma waves overlaid with eye movements“ You know , I know this steak doesn't exist. I know that when I put it in my mouth, the Matrix is telling my brain...that it is juicy...and delicious. After nine years, you know what I realize? Ignorance is bliss. ” Cypher The MatrixToo deep?Too light?  A proprietary ‘black box’ system  Always known to involve Fourier transformations  Always controversial; a ‘random number generator’?  B-Aware trial (Lancet 2004) The trouble  B-Unaware trial (NEJM 2008) with BIS  Cochrane reviews  In ICU population (2018)  In perioperative population (2019)  Regarding rates of POCD & delirium  Expensive consumables (around $45.45 each) 6Engineering breakdown of BISBIS reverse engineered 7 8  Disassembled , emulated and reimplemented by Connor  Not bispectral  Multiple algorithms, not one  Erroneous calculation of SEF  An isoelectric EEG for 3 minutes results in an SEF of 30HzBIS calculationBIS calculation 9 1. EEG epochs are converted into a power spectral density by Fourier transform 2. Subsequent calculations depend upon the relative power distributions across the whole frequency range and across sub-bands spanning 0.5 to 4 Hz (low, slow- delta), 11 to 20 Hz (mid, alpha-beta), 30 to 47 Hz (high, gamma), and 40 to 47 Hz (very high, gamma). 1. General anaesthesia is calculated from difference in power concentration between the 40-47 Hz band and the power concentration over the entire spectrum 2. between the 11-20 and 30-47 Hz frequency bandsverage of the difference in power in dBμV 3. Burst suppression calculated using a proprietary algorithm called QUAZI  At high levels of burst suppression, the score becomes linear with regard to BSR; the output score is given exactly by 50 – BSR/2 when the BSR is at least 50%  Three scores are ‘mixed’; in general, the lowest score ‘wins’  Change in weighting explains directional delay on induction and emergenceBIS and the BSR algorithm 34pEEG directional delay 35Using common pEEG monitors BIS, Narcotrend, E-entropy and SedlineThe BIS display 17Signal Quality Index (SQI)  Signal quality, maximum 100  Ideal SQI ≥80  SQI < 50 indicates poor signal quality  SQI <20 will not calculate a BIS  Tends to fall as EMG rises  Affected by  Ambient electromagnetic fields (table, lights, etc)  Surgical diathermy  Electrode displacement or damage  Poor electrode placementElectromyogram (EMG)  Muscle activity, maximum 100  Target EMG ≤30  An increase in this (even with a low BIS score) could indicate a lack of analgesia  Fully paralysed patients should not have an EMG >30  Unrelated to level of consciousness  Generally derived by electrode 4Suppression ratio (SR)  The proportion of EEG suppression within any given minute, maximum 100%  Should be zero at all times  A SR >0 indicates very deep anaesthesia or anaesthetic coma  Beware misinterpreted ECG signalsSpectral edge frequency 13 (SEFx)  Frequency below which x% of EEG energy is found, given in Hertz  SEF90 or SEF95 are usual (SEF95 on BIS)  Studies have suggested 8–13Hz as the optimal SEF to achieve adequate general anaesthesia  Dependent on multiple factors  Age  Agent  Opiates  10-15 Hz appears a pragmatic compromiseBIS display  BIS number 17  60-80 for sedation  40-60 for anaesthesia  EMG  Marker of muscle relaxation only  SEF95  Aim for 10-15  SQI  Marker of signal quality  SR  Ratio of burst suppression  Aim for zero  Single-channel waveform  Spectrograph BIS optimisation  Ensure EEG waveform is displayed on screen  Optimise scale  100-200μV for children  50-100μV for adults  25-50μV for the elderly  Suppression ratio ON  Filter OFF  These tips apply to E-Entropy as wellNarcotrend  EEG classification A-F  Based on Kugler  E is target for GA  EEG index  Proprietary algorithm  Single-channel waveform  Density spectral array Grade Behaviour Features A0 Alert α, β, γ - normal variants A1 α - diffusion (anteriorisation) A2 Sub-vigilance α - low amplitude, sparse, slow B0 θ - low amplitude, isolated α B2 Drowsy θ - moderately high amplitude, δ - sparse/low-amplitude C0 θ - high amplitude, δ < 30% of time C1 Light sleep θ - high amplitude, δ < 50% of time C2 θ - high amplitude, slow, continuous D0 δ - <30% of time, wide K-complexes D1 Medium sleep δ - <50% of time D2 δ - <80% of time E0 δ - constant, extremely high amplitude E1 Deep sleep δ - constant, extremely slow and high amplitude E2 Smooth, periodic slow bursts (<2 seconds) F0 Anaesthetic coma >2 but <20 seconds burst suppression F1 >20 seconds burst suppression B/REM Rapid Eye Movement Low, high frequency A1-B2 with eye movement 11,12,20 Kugler EEG system 32 E-Entropy  Measures irregularity in spontaneous brain and facial muscular activity  Proprietary EEG and frontal EMG processing algorithm produces two values; the ‘fast reacting’ response entropy (RE) and the ‘steady state’ state entropy (SE)  Highly irregular signals with variation of wavelength and amplitude over time produce high values of entropy and may indicate that the patient is awake  More ordered signals with less variation in wavelength and amplitude over time produce low or zero entropy values, indicating suppression of brain electrical activity and a low probability of recall  RE scale ranges from 0 (no brain activity) to 100 (fully awake)  SE scale ranges from 0 (no brain activity) to 91 (fully awake)  Target range for entropy values is 40–60  RE and SE values near 40 indicate a low probability of consciousnessSedline  4-channel EEG  Proprietary ‘patient state index’  0-100  25-50 optimal for GA  Density spectral array  EMG  BSR  Artifact pEEG utility  Possibly reduces rates of AAGA  Good marker of trends  Marker of intrinsic brain vulnerability  Useful to ensure that the patient is not too deeply anaesthetised  Avoidance of delirium  Clearer & more rapid wake-up  Number to write down to defend against claims of awarenesspEEG utility  TCI is a gain switch  Real concentration in plasma is irrelevant for titration  Effect site must be targeted as it is the site of effect All patients respond differently to different concentrations  Effect must be measured without delay  BIS is 15-30 second behind reality  Ce cannot be measured  Time to peak effect influences TCI bolus, varies between models Beware Eleveld in the elderly  Raw EEG is the only immediate measure  Monitor raw EEG and note relevant TCI values EEG waveform interpretation 10 Spectral frequency bands Name Frequency range (Hz) Slow <1 Delta (Δ) 1-4 Theta (θ) 5-8 Alpha (α) 9-12 Beta (β) 13-25 Gamma (γ) 26-80Progression through deepening sedation33Raw EEG sleep stages 10EEG spectrography 10Propofol spectrographEEG spectrographs of selected agents 10EEG spectrographs of the volatiles10 Grade Behaviour Features A0 Alert α, β, γ - normal variants A1 α - diffusion (anteriorisation) A2 Sub-vigilance α - low amplitude, sparse, slow B0 θ - low amplitude, isolated α B2 Drowsy θ - moderately high amplitude, δ - sparse/low-amplitude C0 θ - high amplitude, δ < 30% of time C1 Light sleep θ - high amplitude, δ < 50% of time C2 θ - high amplitude, slow, continuous D0 δ - <30% of time, wide K-complexes D1 Medium sleep δ - <50% of time D2 δ - <80% of time E0 δ - constant, extremely high amplitude E1 Deep sleep δ - constant, extremely slow and high amplitude E2 Smooth, periodic slow bursts (<2 seconds) F0 Anaesthetic coma >2 but <20 seconds burst suppression F1 >20 seconds burst suppression B/REM Rapid Eye Movement Low, high frequency A1-B2 with eye movement 11,12,20 Kugler EEG systemK-complex Electrode placementThe 10-20 system21pEEG electrodes  Generally looking at the brain as a whole  So long as sufficient neural tissue is between the electrodes, useful readings will be generated  Multi-channel systems (Sedline, raw, bifrontal BIS) excepted  Various electrode placement positions described in literature  Auricular most common  Useful for bifrontal cranial surgery  Easiest with ECG dots (raw, Narcotrend) or needle electrodesAuricular22 25 MandibularNasal22,26Infraorbital28Supralabial29 24,27 Bilateral placementSummary Summary  pEEG background and theory  Engineering breakdown of BIS  Use of common monitors  EEG waveform & density spectral array  Electrode placement options Summary  Treat pEEG algorithms with suspicion  Know their uses  Know their limitations  Treat the patient in the round  Understand other generated values  Spectral edge frequency  Burst suppression ratio  Signal quality index/artefact  Optimise your monitor based on the patient in front of you  Understand what EEG waveform and DSA you should seeUseful resources ICE- IARS EEG for Purdon et TAP anesthesia al.References 1. 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