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I&M for Anesthesia - Fall 2013 > BIS > Flashcards

Flashcards in BIS Deck (43):
0

Components of anesthesia

Unconsciousness/hypnosis
Analgesia
Muscle relaxant

1

Levels of unconsciousness

Perception of explicit memory
Perception and no explicit memory
No perception and implicit memory
No perception and no memory

2

Explicit memory

Refers to intentional or conscious recollection of prior experiences

3

Implicit memory

Information not associated with any conscious recollection
Recall may occur during dreaming, hypnosis, or other psychological methods

4

Percent of legal claims against anesthesia providers

Two

5

Worst thing they have ever experienced

Awareness under anesthesia

6

How big of a problem is awareness?

More common than necessary
One of every thousand patients
Three of every thousand cardiac patients
Up to forty eight with severe trauma

7

Individual patient response variance to anesthetic

Unique tolerance (some predictable, others not)
Fluctuations in hemodynamics stability

8

Circumstantial variance in anesthetic requirement

Surgical stimulus
User error
Delivery device failure

9

Measuring depth - clinical signs

Heart rate
Blood pressure
Sweating
Lacrimation
Pupil diameter

10

Measuring depth - isolated forearm technique

Tourniquet applied to one arm prior to MR

Spontaneous movement or movement to command indicates light anesthesia

11

Measuring depth - skin impedance

Quantitative measure of sweat production

Factors that affect sweating (atropine, autonomic neuropathy) reduce accuracy

12

Measuring depth - surface electromyelogram

Only useful in patients that are not receiving full MR

13

Most widely applied technology for measuring anesthetic depth

EEG

14

Last sense to be suppressed by anesthesia

Auditory

15

Used alone or in combination with EEG

Auditory evoked potentials

16

BIS index range

0 flatline
0-20 burst suppression
20-40 deep hypnotic state
40-60 GA
60-80 moderate sedation
80-100 responds to normal voice
100 awake

17

Moderate sedation

Responds to loud commands or prodding, shaking

18

General anesthesia

Low probability of explicit recall
Unresponsive to verbal stimulus

19

BIS is used to

Prevent patient awareness
Titrate anesthetic to prevent OD
Facilitate faster wake ups, shorter PACU stays
Cost savings

20

How does BIS work

Analyzes analog EEG signal and incorporates facial EMG

Plugged into proprietary algorithm

21

EEG is

Recording of electrical activity along scalp

Arises from ion currents across cell membrane of neurons with similar spatial orientation

22

Contribute most to EEG signal

Pyramidal neurons of the cortex

23

Beta
Alpha
Theta
Delta

Awake
Eyes closed
Light sleep
Deep sleep

24

First order EEG analysis

Looks at amplitude mean and variance
Identifies periods of EEG suppression

25

EEG depression is defined as

At least a .5 second interval during which the EEG voltage does not exceed plus or minus 5 mV

26

Suppression ratio

Ratio of time over the previous 63 seconds that the EEG waveform exhibited suppression

27

Second order EEG analysis

Fourier analysis of the EEG waveform parses out the individual frequency components, creating a power spectrum

Displayed as a compressed spectral array (CSA) or density spectral array (DSA)

28

Spectral edge frequency (SEF)

Frequency below which certain percentage of the power signal is located
Has been studied as an independent predictor of anesthetic depth
Poor positive predictive values for awareness

29

The cutoff range for SEF

14-15 Hz

30

SEF can be higher than 15 Hz during

Deep anesthesia or burst suppression

31

EEG third order (bispectral) analysis

Measures correlation of phase between different frequency components
Physiological significance unclear
May be helpful for noise reduction

32

Why are normal monitors important when using EEG and BIS?

Monitors are not intuitive
Information given is only as good as the info they get
Programmed to identify and disregard common artifact, but are not perfect

33

What do we know about the BIS algorithm?

Incorporates suppression ratio, power spectrum analysis, bispectral analysis of frontal EEG as well as facial muscle EMG

EMG is high weighted component

34

The relationship between BIS and SR

Linear

SR 50 = BIS 20
SR 100 = BIS 0

35

BIS waveforms - pre MR and post MR

Pre - high frequency background fuzziness

Post - cleaner, underlying spindles and delta

36

Sources of noise

Electrocautery
Forced air warmer
Cardiac pacemaker
Hair shaver
Endless others

37

Limitations to BIS

Signal processing lag time - can range from 14-155 seconds

Failure to account for certain drugs with known anesthetic effects - ketamine, N2O, xenon, dexmedetomidine?

38

T or F. Sevoflurane and isoflurane exhibit more BIS reduction than halothane

True

39

Paradoxical changes

Increase in BIS with deepening anesthetic

Decrease in BIS just prior to awakening

40

Pathophysiologic conditions leading to reduction in BIS

Hypoglycemia
Decrease in CBF
Focal or global brain pathology
Hypothermia

41

Beta adrenergic agents epinephrine, ephedrine, and isoproterenol have all been shown to

Increase BIS

Not seen with phenylephrine (pure alpha adrenergic agonist)

42

B-Aware trial

Lower awareness rate in BIS group vs routine
Episodes of awareness occurred when 55-59 and 79-82
Decreases awareness in 82% in high risk adults having GA