[Sudden increases and decreases in bispectral index values more than 30 within 1 minute during general anesthesia]

We described, in a 40-year-old man, sudden and unexpected increases in bispectral index values during the general anesthesia with total intravenous anesthesia using propofol in a dental surgery. The patient was administered continuous infusion of propofol and remifentanil, and intermittent supplementation of fentanyl. Immediately after the beginning of surgery, the bispectral index value increased abruptly to 90; whereas, heart rate and non-invasive blood pressure were unchanged and no physiological finding was observed. Approximately 25 min later, the value decreased to below 40 without any modification of anesthesia. The extent of unanticipated increase might be compatible with the duration of surgical procedure using dental air turbine. Therefore, the noise from surgical device might induce unpredictable change in bispectral index values.