Can the bispectral index be used to predict seizure time and awakening after electroconvulsive therapy?

The electroencephalogram (EEG) bispectral index (BIS) measures the hypnotic component of the anesthetic state and correlates with emergence from general anesthesia. Therefore, we hypothesized that the BIS would be useful in predicting electroconvulsive therapy (ECT)-induced seizure times and awakening from methohexital anesthesia. Twenty-five consenting patients with major depressive disorders underwent 100 maintenance ECT treatments. All patients were premedicated with glycopyrrolate 0.2 mg IV, and anesthesia was induced with methohexital 1 mg/kg IV. The BIS was monitored continuously, and the values were recorded at specific end-points, including before anesthesia (baseline), after the induction of anesthesia (pre-ECT), at the end of ECT (peak), after ECT (suppression), and on awakening (eye opening). The pre-ECT BIS value correlated with the duration of both the motor (r = 0.3) and EEG (r = 0.4) seizure activity (P < 0.05). The peak post-ECT BIS value correlated with the duration of the EEG seizure activity (r = 0.5) (P < 0.05). A positive correlation was also found between the EEG seizure duration and the time to eye opening (r = 0.4) (P < 0.05). However, the BIS values on awakening from methohexital anesthesia varied from 29 to 97 and were <60 in 75% of the cases. We conclude that the BIS value before the ECT stimulus is applied could be useful in predicting the seizure time. However, the BIS values on awakening were highly variable, suggesting that it reflects both the residual depressant effects of methohexital and post-ictal depression.