The effect of facial muscle contractions on the cerebral state index in an ICU patient: A case report
© Borjian Boroojeny; licensee BioMed Central Ltd. 2008
Received: 30 June 2008
Accepted: 19 September 2008
Published: 19 September 2008
Cerebral state monitor is a monitor which shows depth of anesthesia in a number between 0–100 as cerebral state index, in which 40–60 is appropriate for general anesthesia. The effect of electromyogram on cerebral state index has not been shown yet.
A 24-year-old Iranian-balooch man admitted in the intensive care unit because of head injury in a car accident. In spite of sustained low level of consciousness, his cerebral state index had significant fluctuations coordinated with electromyogram resulted from facial muscle contractions. After neuromuscular blocking agent prescription, cerebral state index was decreased from about 90 to 40, directly followed the changes in electromyogram.
The Cerebral State Monitor (Danmeter A/S, Odense, Denmark) is a portable, wireless monitor that uses the time and frequency domain analysis, which inputs into a fuzzy logic inference system to show a 0 to 100 scale, the Cerebral State Index (CSI), with 40 to 60 indicating an adequate depth of hypnosis . In a study, the CSI had a predictive probability statistic for depth of anesthesia of 0.87, which demonstrates good performance . Moreover the CSI performed better for deeper levels of anesthesia than the other brain monitor, BIS(Aspect Medical Systems, Norwood, MA, USA), which was better at lighter levels. There is not any report about the effect of the electromyogram (EMG) signal which may artificially increase the CSI number. EMG signal is high frequency, but it is possible to overlap with low frequency CSI signal. Such interference can be seen with another monitor of depth of anesthesia, BIS [3, 4]. If the CSI is shown artificially high in an ICU patient, probably the sedation of the patient will be decreased which can lead to premature awakening and increase intra cerebral pressure and death. So understanding the limitations and disturbing factors of the CSI which is a useful monitor in the ICU and operating theater, is very important, because wrongly decision making on the basis of a false CSI can be life threatening.
The aim of the Cerebral State Index (CSI) is to monitor the level of consciousness or hypnosis during general anesthesia or in the ICU. The CSI is a unitless scale from 0 to 100, where 0 indicates a flat electroencephalographic signal and 100 indicates the awakening state. The 40–60 range is adequate range for anesthesia. The CSI requires three electrodes positioned at the middle forehead, left forehead, and left mastoid. Alternatively, the right forehead and right mastoid can be used.
The CSI is calculated based on four sub parameters of the electroencephalogram:
Alfa ratio, Beta ratio, Alfa ratio – Beta ratio, and burst suppression, calculating an index from 0 to 100. The novelty of the CSI is that a fuzzy inference system was used in Inference System (ANFIS). During burst suppression, the Alfa and Beta ratios are no longer monotonously decreasing as a function of anesthetic depth, and therefore, they cannot be used in the calculation of the final index . Calculating CSI needs high frequency EEG as well as low frequency, the high frequency component of EEG (that is above 30 Hz) overlaps with EMG frequency starting from 30 Hz up to 42.5 Hz, which is the upper limit of EEG usage for CSI calculation . To our knowledge, the misinterpretation of EMG as EEG can be occurred in Beta Ratio component of bispectral index(BIS), but there not any published papers about such effect regarding to CSI . Omitting or filtering out the 30 Hz or more frequency component of EEG is not acceptable because of the importance of the component in evaluating of hypnosis. Using neuromuscular blocking agents in clinical and short period probably can not directly affect depth of hypnosis, and its monitoring, except response entropy, which is the only commercially available depth of anaesthesia index in which facial EMG activity is included in the calculation algorithm .
In conclusion, CSI can be used for detecting depth of anesthesia or sedation, but overlapping EEG with EMG is an important and sometimes very hazardous pitfall. Wrong assessment of depth of anesthesia can lead to administrate so many anesthetic or hypnotic drugs with many life threatening adverse effects in operating theatre, or misinterpretation of the brain condition of the patient causes premature weaning of the sedation and ventilatory support of the patient.
Written informed consent was obtained from the patient's family for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
cerebral state index
cerebral state monitor
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