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Year : 2012  |  Volume : 6  |  Issue : 1  |  Page : 82-83

Changes in bispectral index values can predict post-ictal phase during awake craniotomy

Department of Neuroanesthesiology, Neurosciences Center, All India Institute of Medical Sciences, New Delhi, India

Correspondence Address:
Tumul Chowdhury
Department of Neuroanesthesiology, Neurosciences Center, All India Institute of Medical Sciences, New Delhi 110 029
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1658-354X.93072

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Date of Web Publication21-Feb-2012

How to cite this article:
Chowdhury T, Sukhlecha C, Prabhakar H. Changes in bispectral index values can predict post-ictal phase during awake craniotomy. Saudi J Anaesth 2012;6:82-3

How to cite this URL:
Chowdhury T, Sukhlecha C, Prabhakar H. Changes in bispectral index values can predict post-ictal phase during awake craniotomy. Saudi J Anaesth [serial online] 2012 [cited 2020 Oct 21];6:82-3. Available from:


Bispectral index (BIS) monitoring has been validated for measuring the depth of anesthesia intraoperatively. [1],[2] Besides hypnosis, BIS values are found to be affected by various factors like hemodynamic alterations, type of anesthetics, pharmacological agents, hypothermia and dementia. [3],[4],[5] We report a case in which low values of BIS were not correlating with the level of consciousness.

A 35-year-old female admitted to our hospital with chief complaints of left-sided focal seizures since 15 years, with an increased frequency since the last 3-4 months. Routine laboratory investigations were within normal limits. She was on tab phenytoin 100 mg tds. She was scheduled for an awake (right fronto-parietal) craniotomy. Routine monitors were attached and BIS monitoring was also recorded. Infusion of dexmedetomidine was started at 1 μg/kg over 10 minutes, followed by maintenance dose of 0.3 μg/kg/hr. In the scalp, six nerves were blocked bilaterally with 0.25% bupivacaine (total volume 25 ml). BIS values were kept between 70 and 80 (mild sedation). Dexmedetomidine was stopped after the dural opening to allow the neurological examination following stimulation to the cortical areas by the surgeon. Just before stimulation, the BIS value was 92. The patient was fully conscious and following the commands. After the first cortical stimulation, suddenly the patient had an episode of generalized tonic clonic seizure. Cortical stimulation was removed immediately and freeze cold saline was irrigated over the stimulated surface and continued until the seizure got resolved in 3-5 minutes. During this period, we observed that the BIS value decreased from 92 to 43, and within 3-5 minutes, the values again reached 90. During this post-ictal period, the BIS values were low (43-56), still our patient was awake. Two such episodes of seizures on cortical stimulation were recorded with similar changes in the BIS values. A complete excision of the tumor was done. Dexmedetomidine infusion was restarted to maintain an adequate level of sedation after the tumor removal and continued till skin closure. After the surgery, the patient was fully awake with no neurological deficit and was shifted to ICU and had an uneventful postoperative recovery.

Antiepileptics are found to decrease BIS values due to their negative action on neuronal excitation and probably by causing sedation. In our patient, baseline BIS value was 94. However, we used dexmedetomidine as a sedative agent which can also affect the BIS values, but it was discontinued just after the dural opening. In our patient, BIS value decreased to 43, which may be due to exhausted neuronal activity in post-ictal phase. [6] In our case, the stimulation area was continuously irrigated with cold saline, and this could be another possible mechanism for decrease in BIS value. Systemic moderate hypothermia is known to cause low BIS values as it decreases neuronal discharge, but literature search shows a lack of reports regarding the effect of cold saline irrigation to brain and BIS values. In our patient, there was rapid rise in BIS values. So, the cause of hypothermia was unlikely because it would take some time to normalize the temperature of brain tissue. Further studies are required to demonstrate the relationship of BIS values and brain hypothermia. So, the intraoperative fluctuations seen in BIS values may not always be a true reflection of the depth of anesthesia and the rise of BIS value to baseline after episodes of seizures may predict the period of post-ictal phase.

  References Top

1.Todd MM. EEGs, EEG processing, and the bispectral index. Anesthesiology 1998;89:815-7.  Back to cited text no. 1
2.Kissin I. Depth of anesthesia and bispectral index monitoring. Anesth Analg 2000;90:1114-7.  Back to cited text no. 2
3.Sakai T, Singh H, Mi WD, Kudo T, Matsuki A. The effect of ketamine on clinical endpoints of hypnosis and EEG variables during propofol infusion. Acta Anaesthesiol Scand 1999;43:212-6.  Back to cited text no. 3
4.Detsch O, Schneider G, Kochs E, Hapfelmeier G, Werner C. Increasing isoflurane concentration may cause paradoxical increases in the EEG bispectral index in surgical patients. Br J Anaesth 2000;84:33-7.  Back to cited text no. 4
5.Bruhn J, Bouillon TW, Shafer SL. Electromyographic activity falsely elevates the bispectral index. Anesthesiology 2000;92:1485-7.  Back to cited text no. 5
6.Nishihara F, Saito S. Pre-ictal bispectral index has a positive correlation with seizure duration during electroconvulsive therapy. Anesth Analg 2002;94:1249-52.  Back to cited text no. 6


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