Gima 35145, User Manual

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The monitor also on-line evaluates the amount of instantaneous burst suppression (BS) in each thirty-second
period of the EEG. This measurement quantifies the amount of “silent” or “flat” EEG period characteristic of
the deepest levels of hypnosis.
These four parameters are used as input to a fuzzy logic classifier system that calculated the Cerebral State
Index.
• CSI Scale
The CSI is a unit-less scale from 0 to 100, where 0 indicates a flat EEG and 100 indicates EEG activity cor-
responding to the awake state. The range of adequate anaesthesia is designed to be between 40 and 60.
All values in the table are approximate values based on the mean values of the patient behaviour.
• EMG
Facial EMG may increase the CSI under certain conditions. The monitor incorporates an EMG filter that re-
moves 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 receive by the patient during surgery. In the presence
of hypnotically unrelated EMG, administration of a neuromuscular blocking agent will cause the CSI to de-
crease. Since patients receiving neuromuscular blocking agents cannot exhibit movement as a sign of arousal,
the CSI is a valuable tool in their anaesthetic management.
• BS% Indicator
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.