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EMG
5.4
High levels of facial muscular or electromyographic (EMG) activity can interfere with the CSI under
certain circumstances. The monitor incorporates an EMG filter that removes most of the potential
interfering EMG activity. The EMG bar shows the energy of the EMG level in the 75–85 Hz frequency
band (0–100 logarithmic). The bar is located on the right side of the display.
EMG activity is expected to be present when the patient is awake. When the patient is asleep, EMG
activity can increase due to:
•
Reflex reactions to painful stimuli during surgery.
•
Lack of muscular relaxation.
•
Muscular rigidity caused by some opioids (analgesics).
•
Presence of large external electrical fields, e.g. diathermy.
The EMG bar should be checked frequently, especially in case of a sudden increase in the CSI. If the
increase in CSI is accompanied by an increase in muscular activity, there is a risk that EMG is causing
interference. When this happens, attention must be paid to the stimuli received by the patient during
surgery. In the presence of hypnotically unrelated EMG, administration of a neuromuscular blocking
agent will cause the CSI to decrease. Since patients receiving neuromuscular blocking agents cannot
exhibit movement as a sign of arousal, the CSI is a valuable tool in their anesthetic management.
Burst Suppression Indicator
5.5
The monitor includes a Burst Suppression indicator to show periods when the EEG is iso-electric or
"flat". The indication appears in the upper left-hand side of the graph window in the display and
shows the percentage of burst suppression over the last 30 seconds of the EEG signal. A BS% = 20
readouts means that the EEG has been iso-electric during 20% of the last 30 seconds.
Artifact and Noise Control
5.6
The artifact rejection algorithm ensures that the incoming EEG is not contaminated with noise. When
excessive noise is detected, the signal quality index is reduced reflecting the disturbance. The
artifact rejection algorithm will be active especially when diathermy and equipment creating external
interference is used.
Cerebral State Monitor - CSM DFU
Page 16
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