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Boards: Monitoring > EEG > Flashcards

EEG Flashcards

1
Q

Advantages of EEG Monitoring

A
  • Monitoring of depth when unable to access head
  • Traditional sites/methods of monitoring eg eye position, m tone unreliable in face of NMBA
  • Reflection of hypnotic properties only
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2
Q

Disadvantages of EEG

A
  • Subject to large drug variations
  • Conflicting information: arousal pattern or deeper level of ax depending on magnitude of stimulus, level of anesthesia
  • No reflection of analgesic properties
  • Not more accurate than physical monitoring of depth
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3
Q

General EEG Patterns

A

o Low‐amplitude, high‐frequency wave pattern during awake state
high‐amplitude
Low‐frequency pattern during ax to burst suppression (intermittent periods of electrical silence)
o Persistent electrical silence with deep levels of anesthesia

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4
Q

EEG Limitations

A
  • Requires vol of recording, specialized training/expertise for interpretation
    o EEG voltage (power) changes as function of time (time domain)
    o Generation of indices: total EEG power (TOTPOW), median power frequency, burst suppression
    o Interpretational algorithms (Fourier transformation): signal activity as function of frequency (frequency domain)
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5
Q

SEF95

A

spectral edge frequency 95: frequency below which 95% of total EEG power resides

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6
Q

MF

A

= Median frequency, median EEG power frequency

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7
Q

delta

A

0.5-3.5Hz

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8
Q

theta

A

3.5-7.0Hz

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9
Q

alpha

A

7-13Hz

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10
Q

beta

A

13-30hz

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11
Q

EEG Frequencies?

A

Dinner Tonight is Alfredo with Broccoli
delta 0.5-3.5
Theta 3.5-7
Alpha 7-13
Beta 13-30

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12
Q

Bispectral Index

A

EEG that quantifies degree of ax-induced cortical depression, represents weighted value derived from four subparameters
 Burst suppression ratio (time domain)
 QUAZI value (time domain)
 Beta2 power ratio in 30–47 Hz range vs 11–20 Hz range (frequency domain)
 Bispectral biocoherence ratio of peaks in 0.5–47 Hz range vs 40–47 Hz range (frequency domain)

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13
Q

Advantages of BIS

A

No calibration required, bar graph – signal quality, amt of muscle artifact

Used to help assure that patients are well anesthetized, pain-free, unaware

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14
Q

Disadvantages of BIS

A

Excessive m movement can interfere with BIS computation

BIS index highly variable in dogs, did not track ETiso well

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15
Q

MAC(BIS)

A

MAC at which nociceptive stimulus causes increase in BIS to 60 (cats)

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16
Q

BIS: Effect of different anesthetics

A

 Strong depression: propofol, midaz, TP
 Intermediate effect: inhalants
 Little effect: opioids
 Increase BIS: ketamine, N2O

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17
Q

BIS Measurements

A
  • Quantitative, 0-100
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18
Q

BIS >90

A

compatible with awake, alert

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19
Q

BIS 80-90

A

anxiolysis

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20
Q

BIS 60-80

A

with moderate obtundation
* 60-70: compatible with completion of sx in dogs

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21
Q

BIS <60

A

Loss of recall

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22
Q

BIS <50

A

Unresponsive to verbal stimuli

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23
Q

BIS <40

A

loss of muscular movement in response to a noxious stimulus

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24
Q

BIS <20

A

burst suppression (deep anesthesia)

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25
Q

BIS 0

A

isoelectric activity

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26
Q

Cerebral state index (CSI) using a cerebral state monitor (CSM)

A

o 3 clip electrodes: forehead (+), occipital (-), parietal (reference)
o Index calculated via algorithm of two energy bands (beta, and alpha), B:A ratio, burst suppression (BS)
 BS: quotient that considers time to zero EEG activity
 EEG, CSI, BS, EMG, signal quality index (SQI)

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27
Q

CSI >90

A

Awake

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28
Q

CSI 80-90

A

sedation

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29
Q

CSI <80

A

Unconscious

Anything lower not correlated well with physical signs of depth

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30
Q

Narcotrend

A

Auditory evoked EEG responses used primarily to assess neurologic function, CNS disease
 Also used to assess depth and awareness/recall

Analyzes raw EEG data, categorizes level of sedation:

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31
Q

Narcotrend: A0

A

Awake

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32
Q

Narcotrend: A1/A2

A

Subviligant

33
Q

Narcotrend: B0/B1/B2

A

sedation

34
Q

Narcotrend: C0/C1/C2

A

Ax

35
Q

Narcotrend: D0/D1/D2

A

Moderate Ax

36
Q

Narcotrend: E

A

Deep anesthesia, burst suppression

37
Q

Narcotrend: F

A

coma/electrical silence

38
Q

Electroencephalography

A

○ Recording of spontaneous electrical brain activity from scalp electrodes
■ Surface signals represent summation of activity from millions of neurons in the cerebral cortex
■ Result from excitatory and inhibitory Postsynaptic Potentials (PSPs) in large pyramidal neurons located in the lower layers of the cerebral cortex
○ Amplitude and frequency are modulated by AFFERENT inputs from sensory-specific thalamic nuclei

39
Q

Gamma bands

A

Problem solving, concentration

EnGrossment

40
Q

Beta bands

A

Busy, active mind

41
Q

Alpha bands

A

Reflective, restful

alPha _ pensive

42
Q

Theta bands

A

drowsiness

T for tired

43
Q

Delta bands

A

sleep, dreaming

D for dreaming

44
Q

EEG Activity

A

activity associated with consciousness is generated from pacemaker neurons within ascending reticular activating system (ARAS)

mediated, modulated through thalamic connections
■ Pacemaker neurons oscillate 8-12 Hz
■ 𝛂 rhythm dominates resting EEG

45
Q

Awake State

A

consciousness maintained by circulating activity among ARAS, intralaminar nuclei, cerebral cortex
■ Additional sensory stimulation will cause cortical arousal → desynchronization of 𝛂 oscillators with appearance of a faster rhythm in the 𝛃 frequency range (12-25 Hz)
■ Desynchronization: shift in EEG pattern from LOW-voltage, FAST-wave to a HIGH-voltage, SLOW-wave pattern

46
Q

As anesthetic depth increases…

A

predominant EEG pattern characterized by DECREASE in 𝛃, INCREASE in 𝛂/𝜭 (anteriorization with loss of consciousness LOC)

47
Q

Progression of Anesthetic Depth

A

, 𝛅 and 𝜭 waves appear in Centroposterior regions with subsequent anterior spread

48
Q

Very Deep Anesthesia

A

indicated by flat areas with interspersed 𝛂 and 𝛃 activity (Burst Suppression Pattern) followed by a complete loss of electrical discharged (isoelectricity or electrical silence)

49
Q

EEG synchronization or desynchronization during anesthesia associated with clinical signs

A

mydriasis, hypertension, and/or tachycardia
● Poor correlation between EEG and hemodynamic responses to noxious stimulation reported

50
Q

Power-Spectrum Analysis

A

computer-processed EEG analysis has been employed for 30+ years
■ Minute-to-minute assessment of anesthetic depth
■ Produce Quantitative EEG (QEEG)

51
Q

QEEG

A

● Median frequency (MF)
● Spectral edge frequency (SEF)
● Percentage distribution of total power into the frequency bands
● Power band ratios: 𝜭/𝛅 ; 𝛂/𝛅; 𝛃/𝛅

52
Q

CSA: Compressed Spectral Array

A

allow readability of EEG

Hills and valleys in the CSA represent frequency bands with higher and lower power, respectively

53
Q

CSA: Increasing ax depth

A

○ increase in total power, increase in relative power of 𝛅 and 𝜭; decrease in 𝛂 and 𝛃, decrease in MF/SEF

54
Q

CSA: decreasing ax depth

A

Shift in power from low (𝛅 and 𝜭) to high (𝛂 and 𝛃),
decrease MF, SEF

55
Q

BSR

A

Burst Suppression Ratio

56
Q

Burst Suppression Ratio

A

percentage of isoelectric periods occurring over a certain period of time
■ Burst suppression indicates non-specific reduction in cerebral metabolic activity
● Ex. Trauma, drugs, hypothermia

57
Q

BSR Measurements

A

1 indicates no activity; 0 indicates active brain
● Ratio increases as the brain becomes increasingly inactive

58
Q

EEG isoelectricity: ETiso vs EThalo

A

○ Studies have shown that EEG isoelectricity might be achieved with lower end-tidal Isoflurane concentrations compared to halothane
■ Dogs, horses, rats
■ Anesthetic depth as determined by clinical signs and MAC multiples → Isoflurane produced lower SEF, MF and/or 𝛃/𝛅 ratio values but higher amplitude measures than Halothane

Conclusion: brain reacts more sensitively than spinal cord to Isoflurane

59
Q

Primary Goal of Intraop EEG

A

■ Maintenance of a HIGH-voltage, SLOW-wave EEG
■ Avoid sudden changes to pattern in response to noxious stimuli

60
Q

Types of Evoked Potentials

A

Mid-latency Auditory Evoked Potentials (MLAEPs)
Somatosensory-evoked potentials (SSEPs)

61
Q

SSEPs

A

electrical signals generated by the nervous system following mechanical or electrical stimulation in the periphery and subsequent sequential activation of neuronal structures along the somatosensory pathway
■ Appear as negative waves (Ni- initial; Ns- second) superimposed on was surface positivity (Pi- initial; Ps- second)

62
Q

SSEPs for Most Anesthetics

A

● increase in anesthetic depth indicated by an increase in latency and decrease in the amplitude of Pi and Ni waves
● Decreased depth/Arousal: Decreased latency and increase in amplitude
■ Effects of anesthetics on SSEPs supports that information transfer through the thalamus is interrupted

63
Q

Which two anesthetic agents do not follow the normal rule for SSEPs?

A

Propofol, etomidate

64
Q

Usefulness of Evoked Potentials

A

○ Neither MLAEPs or EEG-derived variables can be used to predict movement response to noxious stimuli → Limited utility for Intraoperative monitoring

65
Q

BIS

A

Index derived from EEG signal processing

Dimensionless number intended to indicate the patient’s level of consciousness
■ Range 0-100
● 100: awake
● 0: isoelectric EEG
● 55: recommended as the upper limit that might assure adequate depth of surgical anesthesia

66
Q

BIS Uses

A

○ Dose-dependent DECREASE in BIS values with increasing ET concentrations/doses (iso, sevo and propofol)
○ No benefit found with BIS monitoring compared to end-tidal anesthetic agent concentration (ETAC) with respect to avoiding awareness
■ Changing volatile anesthetic concentration based solely on BIS NOT RECOMMENDED
■ Reported to be significantly MORE accurate than targeted or measured propofol concentrations during sedation/hypnosis

67
Q

Nacrotrend Index

A

○ Algorithm based on pattern recognition of the raw EEG
■ Classifies EEG traces into stages from A (awake) to F (burst suppression/isoelectricity)
■ Dimensionless index (NI): 100 (awake) - 0 (isoelectricity)
○ NI and BIS considered equally effective in monitoring anesthetic depth in human patients

68
Q

Otto et al 2012 (NI)

A

Compared NI with clinical signs of anesthesia during experimental cardiac surgery in isoflurane-anesthetized sheep - significant correlation between NI and increasing anesthetic depth

69
Q

Entropy

A

○ EEG parameter based on frequency spectrum analysis (MF, SEF)
■ Reflect linear signal properties
■ Analyzes the irregularity, complexity, and unpredictability of EEG signals

70
Q

Types of Entropy

A
  1. State Entropy (SE)
  2. Response Entropy

■ Dimensionless numbers
■ Overlap of EEG and EMG frequencies (30-50 Hz)
■ At deep levels of anesthesia (EMG power = 0), SE and RE are equal

71
Q

State Entropy

A

computed over EEG-dominate spectrum (0.8-32 Hz)
■ Reflects the Cortical State of the patient

72
Q

Response Entropy

A

Includes EEG and EMG
■ Indirect measure of adequacy of analgesia
■ EMG activity increases as result of nociceptive stimulation and during decreasing levels of anesthesia

73
Q

Entropy Uses

A

○ Recommended range: 40-60
■ SE > 60 → Increase depth of anesthesia
■ RE > 60 → Additional analgesics should be considered
○ Poor performance during ketamine and NO administration

74
Q

Index of Consciousness (IoC)

A

Derived from a combination of symbolic dynamics, 𝛃-ratio and EEG suppression rate

75
Q

IoC Ranges

A

■ 0 = isoelectric
■ 99 = awake
■ 80 = associated with sedation
■ 40-60 = recommended for general anesthesia

76
Q

Cerebral State Index/Monitor (CSM)

A

○ EEG based monitor used to measure the depth of hypnosis during GA

77
Q

Are there any currently used EEG-based monitors that can unfailingly detect wakefulness?

A

NO

78
Q

Electromyography

A

Measurement of the electrical activity within the muscle
■ Needle inserted in muscle
■ Analysis of waveforms and firing rates of single or multiple motor units can give diagnostic information

Boards: Monitoring (19 decks)

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