[Electromyographic activity increases the bispectral index up to 98 during anesthesia]

We report the patients who developed sudden unpredicted increases of bispectral index (BIS) value during sevoflurane and fentanyl anesthesia. After the epidural catheter placement, anesthesia was induced with propofol and fentanyl, and muscular relaxation was obtained by vecuronium for tracheal intubation. Anesthesia was maintained with 1-1.5% sevoflurane, intermittent administration of fentanyl and epidural infusion of ropivacaine. The nociceptive stimuli might be unchanged during the surgical procedure of reconstruction, but sudden increases of BIS value were found. At first, the BIS was decreased with small dose of supplemental anesthetics, but finally, it was up to 98 and the depth of anesthesia could not be assessed by BIS value. Because slight shivering was found in the patient immediately after emergence, electromyographic activity might have falsely elevated the BIS excessively. No clear recall or explicit memory during operation was observed after anesthesia, but anesthesiologists might better pay much more attentions to unpredictable changes of anesthetic depth during anesthesia.