Raw EEG characteristics, bispectral index, and suppression ratio variations during generalized seizure in electroconvulsive therapy

Editor—We wish to report our findings of an observational prospective study of raw EEG characteristics, bispectral index (BIS) and suppression ratio (SR) variations during a generalized tonic–clonic seizure induced by electroconvulsive therapy (ECT). After obtaining the approval of the Ethics Committee for biomedical research, 20 patients were included for a total of 39 sessions. The BIS sensor (BIS Quatro, Medtronic-minneapolis USA) was connected to the BIS-VISTA^® (Medtronic-minneapolis USA) monitor (smoothing rate, 10 s). The BIS and SR values were retained for analysis if their corresponding signal quality index were ≥50 and EMG ≤50. To overcome electromagnetic interference, we excluded from analysis all BIS and SR values obtained from the end of the electrical impulse to 15 s later. Sedation was induced with a bolus of propofol [(median dose 0.86 (interquartile range 0.68–1) mg kg⁻¹] after 3 min of preoxygenation. Suxamethonium [median dose 1.1 (range 1–1.2) mg kg⁻¹] was injected 30 s after loss of the ciliary reflex. Electroconvulsive therapy began at least 30 s after the end of fasciculation and after the stabilization of BIS. The lungs were ventilated until ECT began, in order to avoid hypercapnia. Differences between BIS and SR values were analysed with the Friedman test, and when a significant difference was encountered the trend over time was analysed by a Mann–Kendall test. Statistical significance was assumed at P<0.05.

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