Bispectral index during epidural puncture predicts anterograde amnesia in patients given midazolam premedication

Purpose We hypothesized anterograde amnesia could be predicted by the bispectral index (BIS) during epidural puncture in patients premedicated with intramuscular midazolam. Methods We investigated 64 consecutive patients undergoing gynecological laparotomy under general anesthesia combined with epidural anesthesia. Midazolam (5 mg) was administered intramuscularly at 15 min before arrival at the operating room. The anesthesiologist informed the patient of the operating room number after evaluating her using the Observer’s Assessment of Alertness and Sedation (OAA/S) scale. A BIS probe was then attached to the patient’s forehead while she was in the lateral position for epidural puncture. Another anesthesiologist interviewed the patient on the day after surgery and asked her the operating room number and whether there was recall of pain. Group A comprised patients with no recall of the room number and no recall of pain during epidural puncture and group R comprised patients who remembered both the room number and the pain. Patients recalling only the room number or the pain were excluded. Results Forty patients were classified as group A and 20 as group R. Four patients remembered only the room number and they were excluded. There were significant differences in body weight, OAA/S scale on arrival at the operating room, and average BIS, and electromyogram (EMG) values during epidural puncture between the two groups. These four parameters were entered into a multiple logistic regression model for multivariate analysis. The analysis identified the BIS value as the only independent predictor of complete amnesia during epidural puncture. Conclusion BIS assessment during epidural puncture is informative for the anesthesiologist to predict amnesia following midazolam premedication.