High BIS and low rSO2 during CPB: seizure?
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KeywordsBispectral index Regional cerebral oxygenation saturation
To the Editor:
During cardiac surgery, anesthetists monitor the bispectral index (BIS) and regional cerebral oxygen saturation (rSO2). We report the case of a high BIS score and low rSO2 value during an ascending aorta graft surgery. Anesthesia was maintained with propofol and remifentanil infusion. Immediately after the aortic cross clamp was applied, the BIS abruptly increased to 92, and the rSO2 gradually decreased to 37 on both sides. Midazolam and rocuronium were administered, but little change was observed. Vital signs and an arterial blood gas analysis (ABGA) did not show any problems. The body temperature was 28 °C. About 20 min after the high BIS, the perfusionist began the sevoflurane inhalation via a pump. The BIS then decreased to 40, and the rSO2 slowly increased to above 50. The patient was confused and irritable for 3 days after surgery, but did not show any kind of neurological complications thereafter. He did not recall the surgical experience.
After we ruled out several causes for the aberrant values, we concluded that a seizure might have occurred during the event. Intraoperative seizures have been reported intermittently [1, 2]. During a seizure, cerebral activity is exaggerated and coincides with high electromyography activity, resulting in increased BIS values. When a seizure stops, the BIS decreases to the previous level. The rSO2 decreases because of a high metabolic process in the cerebral hemisphere. After a seizure, the rSO2 increases.
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Conflict of interest
The author(s) declare that they have no competing interests.
- 1.Thakkar K, Mariappan R, Nair B. Detection and management of intraoperative seizure with bispectral index monitoring in a paralyzed patient. Neurol India. 2017;65:S1–S100.Google Scholar