The effect of facial muscle contractions on the cerebral state index in an ICU patient: A case report
Address: Anesthesiology department, medical school, Zahedan university of medical sciences
Introduction: 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. Case report: 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.
A 24-year-old Iranian-balooch man was admitted in the
ICU because of head injury. He had not any history of
medical or surgical diseases before the accident. His CT
scan showed generalized brain edema, the Glasgow coma
scale score (GCS) on arrival was 4. In the ICU the patient
was sedated by remifentanil and midazolam to decrease
the brain edema via hyperventilation and decreasing
blood pressure. Twenty four hours later, the CSI was
appeared with fluctuations that correlated to muscular
twitching in the facial muscles. The CSI had also
fluctuations parallel to EMG activities which appeared on the
CSM screen with a short time delay, less than one minute
(figure 1) . When EMG activity reached to 100%, CSI
became 100, and when it went down to 25%, CSM also
became 2530. All of the CSI data was recorded
automatFCiSgIucruerv1e of the patient
CSI curve of the patient. CSI: cerebral state index, BS: burst suppression, EMG: electromyogram. 1: first injection of
atracurium (25 mg), 2: second injection of atracurium(15 mg). As appeared in the figure, CSI changes follow the EMG changes. BS
increases when EMG decreases.
ically and wirelessly by the company's standard software.
Because of the patient's brain condition; it was very
important to evaluate the level of consciousness. So,
atracurium 25 mg intravenously was injected at 00:36 a.m
leading to disappearing EMG activity three minutes later
except sporadic surges. Concomitant with decreasing
EMG, CSI was decreased from 100 to 70. An interesting
finding was increasing burst suppression (BS) from zero
to about 10% after first injection of atracurium. After
returning EMG at o1:34 a.m, the second dose of
atracurium was injected 15 mg intravenously at 1:36 leading to
complete EMG recession and increasing BS to 2030%
and decreasing CSI to 2040. All of the time GCS was 7
and Richmond Agitation-Sedation Scale remained
between 0 to 1.
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 4060 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
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.
CSI: cerebral state index; CSM: cerebral state monitor; BIS:
bispectral indexl; EMG: electromyogram; BS: burst
suppressionl; EEG: electroencephalogram.
The author declares that they have no competing interests.
The single author was involved in the management of the
case and finalizing the article. The single author was
involved in the process of editing, correcting, and
finalizing the manuscript. The author has read and approved the
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.