Advertisement
Chapter 15: BFA Monitoring
User Manual
15.1 GENERAL
Anesthesiologists have been using hemodynamic and clinical characteristics such as heart rate,
blood pressure, tears, facial variations, pupil diameter and perspiration as well as different
stimulations and personal experiences to measure the level of patient consciousness for many
years. They also use devices such as Capnography and pulse oximetry in this regard. Since none
of these parameters is directly associated with the level of consciousness, Physicians must use
indirect measurement methods to apply appropriate dosage for each patient in order to make the
patient feel no pain during surgery.
There are some standards to determine required dosage for each patient, for example one
standard is based on needs of a middle-aged man. This standard is certainly not suitable for
females, patients of different ages or patients with dangerous and unknown diseases.
There are common cases in which the patient is overdosed (receives excessive amount of drug)
and this results in long wake-up time after anesthesia, prolonged recovery accompanied by
nausea as well as economic loss.
A rare and chronic condition is when the patient receives low amount of drug and does not lose
his consciousness completely (subconsciousness level), but due to the injection of muscle
relaxant drugs he is unable to react during surgery and has a vague picture of what is going on
around him. This can cause long-term emotional consequences and subsequent psychological
traumas. The most of these patients suffer nightmare during few days after surgery.
A lot of attempts were made to measure the level of consciousness using patient vital signs
signals, a method through which the required dosage of drug for each patient can be estimated
without considering physiological factors such as weight, age, etc.
The Brain Function Assessment Monitor (BFA) is a non-invasive measurement tool for use by
trained professionals to measure the level of consciousness (LOC) in all area of the hospital. BFI
index is calculated through EEG signals. BFA module displays the related indexes but does not
perform any data interpretation. All data interpretation is performed by a physician.
The monitor is intended for use in monitoring the hypnotic state of the brain by data acquisition
of EEG signals of the anesthetized or sedated patient in all areas of the hospital.
Measurement principle
An instrumentation amplifier collects ongoing EEG with a high Common Mode Rejection Ratio
(CMRR) ensuring a high-quality EEG acquisition. Special algorithms that eliminate their effects
on subsequent BFI calculations detect artefacts.
The performance of the BFI is based on the analysis of the frequency content and phase of the
EEG signals.
The monitor also evaluates the amount of burst suppression (BS) in each fifty-second period of
the EEG. This measurement quantifies the amount of "silent" or "flat" EEG periods characteristic
of the deepest levels of hypnosis.
15-2
Advertisement
Chapters
