10-3
10.4 Understand BIS Parameters
BIS monitoring provides the following parameters for display as shown below.
Non-Extend sensor Extend sensor
1. Bispectral Index (BIS)
The BIS numeric reflects the patient’s level of consciousness. Typically, it ranges from
40 to 60 for a patient under general anesthesia during surgery.
BIS numeric Description
100 The patient is widely awake.
70 The patient is underdosed but still unlikely to become aware.
60 The patient is under general anesthesia and loses consciousness.
40 The patient is overdosed and in deep hypnosis.
0 The EEG waveform is displayed as a flat line, and the patient has no
electrical brain activity.
2. Signal Quality Index (SQI)
The SQI numeric reflects signal quality and provides information about the reliability of
the BIS, SEF, TP, and SR numerics during the last minute. It ranges from 0 to 100%.
0 to15%: the numerics cannot be derived.
15 to 50%: the numerics cannot be reliably derived.
50 to 100%: the numerics are reliable.
3. Electromyograph (EMG)
EMG bar graph reflects the electrical power of muscle activity and high frequency
artifacts. The minimum possible EMG is about 25 dB.
EMG <55 dB: this is an acceptable ECG.
EMG≤30 dB: this is an optimal EMG.
4. Suppression Ratio (SR)
SR numeric is the percentage of time over the last 63-second period during which the
EEG is considered to be in a suppressed state.
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