Transcript BISPECTRAL INDEX MONITOTING - British Columbia Respiratory

ICU SKILLS UPDATE
February/March 2007
By Dianne Brown
ICU Skills Update
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Theory and Hands On Practice
Bispectral Index Monitoring
BISPECTRAL INDEX
MONITOTING
BISPECTRAL INDEX MONITORING
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The bispectral index (BIS) is a fairly recent
technology used to measure the effects of
anesthetics and sedatives on the brain and
consciousness
Uses a complex mathematical algorithm
based upon descriptive EEG parameters
from the frontal cortex to suggest various
levels of sedation
BISPECTRAL INDEX MONITORING
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A sensor, placed on the patient’s forehead,
sends raw EEG waveforms to the monitor,
where they are analyzed and a BIS index is
calculated
This value ranges from 100 (completely
awake) to 0 (isoelectric EEG)
BISPECTRAL INDEX MONITORING
BISPECTRAL INDEX MONITORING
Understanding the relationship
between BIS and EEG
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When BIS monitoring is initiated, a sensor is
placed across the patient’s forehead per
manufacturer’s recommendations to detect
one channel of EEG activity
The EEG signal is filtered and digitalized
The EEG state (frequency/amplitude) is
calculated and associated with the level of
sedation, arousal or anesthesia
Understanding the relationship
between BIS and EEG
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The BIS value is a single number based on
the previous 15 seconds of EEG data and is
updated frequently
The BIS monitor provides a single channel of
an EEG tracing from the right or left frontaltemporal montage electrode placement
ICU Sedation:
A Bipolar Challenge
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Over-sedation
Patient unable to
participate in care
Delayed weaning
↑Ventilator-associated
pneumonia
↑Unnecessary testing
↑ICU and hospital
length of stay
↑Costs
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Under-sedation
Anxiety, agitation
↑Cost, nursing time
↑Use of neuromuscular
blocking agents
↑Risk of
recall/awareness of
unpleasant events
↑Unintended medical
device removal
Potential Indications for BIS
Monitoring
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Use with neuromuscular blockade: BIS monitoring
may help to identify patients at risk of awareness,
recall and pain when paralyzed
Use of BIS values to guide sedation and analgesia
Titrating sedation/analgesia in patients receiving
controlled ventilation
Avoiding extremes of under and over sedation
Titration of medications for medication-induced
coma
Factors affecting the BIS value
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Sedation: decrease in BIS value
Analgesia: decrease in BIS value
Neuromuscular blocking agents: decrease in
BIS value related to attenuation of highfrequency muscle activity across the patient’s
forehead
Painful (noxious) stimulation: if analgesia
inadequate, arousal response may be
produced within cerebral cortex
Factors affecting the BIS value
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Sleep: BIS range is lower (20-70) during
deep sleep, and BIS range is higher (75-92)
during REM sleep
Hypothermia: decrease in BIS value
Cerebral ischemia: decrease in BIS value
Neurological states: decrease in BIS value
depending of location of injury and degree to
which overall cerebral metabolism is affected
Factors affecting the BIS value
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Encephalopathic states: severe
anoxic/ischemia encephalopathy (decrease in
BIS value)
High-frequency electrical artifact from patient
care equipment, such as pacemaker or
muscle activity; rapid head or eye movement
(increase in BIS value)
Interpretation of BIS value
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BIS is interpreted over time, in response to
stimulation and within the context of whether
therapeutic endpoints and overall goals of
therapy are met
Decisions to increase or decrease titration of
sedative or analgesic should be based on
clinical assessment/judgement, goals of
therapy, and the BIS value
Interpretation of BIS value
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Relying on BIS alone for sedation/analgesia
management is not recommended
Movement such as in response to painful
stimulation may occur with low BIS values
BIS increases suddenly or is
higher than expected
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Is the sedative
sufficient?
Has the sedation been
decreased?
Is there an increase in
stimulation?
Is there any muscle
shivering or pt motion?
Is the NMBA wearing
off?
BIS decreases suddenly or is
lower than expected
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Has been a decrease in
stimulation?
Has patient recently
received NMBA?
Has there been an increase
in sedation?
Is the patient sleeping?
Has the pt recently received
analgesic?
Has there been a sudden
significant drop in BP?
Current Status of the Literature
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BIS scores do not provide a differential
diagnosis. BIS scores can be affected by
many cerebral events including sedation,
sleep and cerebral ischemia
BIS/EEG activity can also be affected by age,
temperature, PaCO2, hyper/hypo-glycemia,
electroyte imbalances, hepatic or renal
function, endocrine disorders
Current Status of the Literature
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BIS scores can be affected by many forms of
artifact:
- Artifact occurs with excessive muscle
activity – movement, swallowing, blinking,
shivering etc.
- Artifact can also occur with concomitant use
of other electrical devices and monitoring
equipment - EEG
Current Status of the Literature
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Neuromuscular activity typically elevates BIS
scores. Hence the effects of NMBAs or their
metabolites may cause lower BIS scores as a
result of decreased muscle activity and not
decreased LOC
The synergistic action of agents affecting
muscle relaxation must be considered when
interpreting scores
Current Status of the Literature
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Overall conflicting research results
May predict recovery of consciousness related to
sedation and possibly traumatic brain injury
Several studies have found variable correlations
between BIS scores and sedation scores
BIS monitoring may serve as an adjunct measure to
subjective scales of sedation monitoring in ICU
patients, particularly in patients who are heavily
sedated or chemically paralyzed
Clinical Applications
BIS is only one part of a multi-modal
assessment strategy
 It remains unclear as to what BIS
actually measures: Awareness?
Hypnosis with recall? Delirium?
Extent of brain injury, brain function or
generalized cerebral electrical
activity?
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Clinical Applications
Only use trended scores
 When interpreting results, consider
multiple factors including
measurements error as well as the
special/individual circumstances of
each patient
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What the numbers mean
BIS Number
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What the numbers mean:
0 = no electrical brain activity
100 = fully awake
For moderate sedation, aim for range from 6070, below 60 is associated with a low probability
of explicit recall
For deeper sedation, aim for range from 40-60.
A patient with a BIS value of less than 45 is
approaching a deep hypnotic state
BIS Number
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For a patient receiving neuromuscular
blockage, sedation, analgesia therapy, the
medication should be titrated for a BIS value
between 45 and 60
SQI: Signal Quality Index
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What the numbers mean: 0 = poor quality
100 = excellent quality
Aim for range from 80-100%
EMG: Electromyographic
Activity
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Reflects the electrical power of muscle activity or
artifact
What the numbers mean: the higher the number, the
greater the muscle activity
- if the EMG is high, can make the number
artificially high (it incorrectly reads the increased
muscle activity as increased EEG activity
Acceptable EMG is less than 55 dB
Optimal EMG is less than 30 dB
Electrode Placement
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Prep skin with alcohol prior to electrode
placement
Electrode should be changed every 24 hours,
alternating temples daily
Look at electrode packaging for placement
instructions
Electrode Placement
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To ensure adequate placement and
impedance, check on the screen
Resources
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Guidelines and Procedure available in AACN
Procedural Manual for Critical Care,
Procedure 86, page 699