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Chapter 15: BFA Monitoring
The measured parameters in BFA monitor are EMG (Electromyography) and SQI (Signal
Quality Index).
BFA Index (BFI)
The BFI is a unit-less index from 0 to 100, where 0 indicates a flat EEG and 100 indicates EEG
activity in awake state. BFI range in 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.
The relationship between BFI and the clinical state of patient is shown in the table below:
80-100 Awake
EMG
High levels facial muscular or electromyographic (EMG) activity can interface with the BFI
under certain circumstance .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 30-
47 Hz frequency band (0-100 logarithmic).
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. electrosurgical unit.
The EMG bar should be checked frequently, especially in case of a sudden increase in the BFI. If
BFI increases along with muscular activity, there will be risk of EMG interference. When this
happens, attention must be paid to the stimuli received from the patient during surgery. In the
presence of hypnotically unrelated EMG, administration of a neuromuscular blocking agent will
decrease BFI. Since patients receiving neuromuscular blocking agents cannot exhibit movement
as a sign of arousal, the BFI is a valuable tool in their anaesthetic management.
Burst Suppression Indicator (BS)
The monitor includes a Burst Suppression indicator to show periods when the EEG is iso-electric
or "flat". The indication appears in the BFI window and shows the percentage of burst
suppression over the last 50 seconds of EEG signal. A BS% =20 readouts means that the EEG
has been iso-electric during 20% of the last 50 seconds. In normal and low level of
BFI
60-80
Light/Moderate sedation
Range considered as adequate for surgical
40-60
anesthesia (General Anesthesia)
Deep anesthesia, in most cases accompanied
20-40
by burst suppression (Deep Hypnotic State).
Close to coma with BS pattern. EEG is
0-20
generally iso-electric (Burst Suppression).
Clinical State
15-3
User Manual
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