Low bispectral index values following electroconvulsive therapy associated with memory impairment

Purpose: It has been reported some patients have opened eyes with low bispectral index (BIS) values immediately following electroconvulsive therapy (ECT). We investigated the time course of the recovery from amnesia and BIS values. Methods: Five patients with depression requiring repeated ECT procedures were enrolled. The patients were asked to recall an object presented prior to anesthesia at four specific points (prior to induction, upon regaining consciousness following ECT, when they returned to their ward, and when their BIS values had returned to pre-anesthetic levels). BIS data were recorded continuously until BIS values returned to the pre-anesthetic levels at their ward. The area under a receiver-operating characteristic (ROC) curve was used to detect associations between the BIS values and disturbance of memory function. Results: A total of 41 ECT stimuli were administered. After returning to their ward, patients generally fell asleep, with BIS values of between 50 and 70, and they woke up 1-2 h later. All the patients could recall the presented object prior to anesthesia and when the BIS values had returned to pre-anesthetic levels. The area under the ROC curve for the detection of memory disturbance was 0.902. Conclusion: The present study demonstrated a high frequency of patients falling asleep and the frequent occurrence of prolonged periods of low BIS values following ECT. The results of memory testing showed that ECT procedures resulted in amnesia. The ROC curve findings suggest a strong association of memory disturbance with BIS values. In conclusion, patients generally fell asleep, with low BIS values, for 1-2 h after ECT, and a prolonged period of impairment of memory formation was associated with low BIS values.