Adjustment of anaesthesia depth using bispectral index prolongs seizure duration in electroconvulsive therapy

Electroconvulsive therapy (ECT) under propofol anaesthesia induces relatively shorter seizures compared to barbiturate anaesthesia. Since significant correlation between seizure duration and bispectral index (BIS) value immediately before electrical stimulus has been reported among patients, adjustment of anaesthesia depth as determined by BIS may be effective in obtaining a longer seizure length. In the present study, we examined this hypothesis in those patients whose muscular seizure duration was less than 40s. ECT was prescribed to 20 patients suffering from endogenous depression. General anaesthesia was induced with propofol 1 mg/kg. Succinylcholine chloride 1 mg/kg was then given. The efficacy of electrical stimulation was determined using a tourniquet technique, electromyogram, and electroencephalography. When a patient had a seizure less than 40s in their second ECT treatment, the subsequent treatment was modified such that the electrical stimulus was given after waiting for a higher BIS value (+10-20). Intensity of electrical stimulus and anaesthesia conditions were identical in the two treatments. All 20 patients had longer seizures as determined by the electromyogram and/or electroencephalography when the stimulus was delivered at the higher BIS value. Seizure duration measured by muscle movement was 31+/-5 s when the stimulus was delivered without waiting and 46+/-10 s when delivered after waiting. There was a significant difference in seizure duration between the two treatments (P<0.01). Waiting for a recovery in BIS value before electrical stimulation can prolong seizure duration.