Depth of Anaesthesia Measured by Patient State Index ( PSi ) Does Not Correlate With Increased Seizure Duration During Electroconvulsive Therapy

Background Seizure duration during electroconvulsive therapy (ECT) correlates with treatment efficacy and may be influenced by depth of anaesthesia. The Patient State Index (PSi), derived from processed EEG, offers a potential method to monitor depth of anaesthesia during ECT. This study examined the correlation between pre‐ictal PSi and EEG‐seizure duration. Methods In this prospective observational study, adult patients undergoing routine ECT at a Swedish university hospital were monitored using the SedLine pEEG system. Anaesthetic care followed standard protocols and the clinical team was blinded to PSi values. Pre‐ictal PSi was defined as the final value prior to the ECT stimulus. EEG‐seizure duration and relevant clinical variables were extracted from health records. The primary outcome was the association between pre‐ictal PSi and EEG‐seizure duration, analysed using a linear mixed‐effects model adjusting for age and use of benzodiazepines or anticonvulsants. Secondary analyses explored sex and age effects on PSi over time and differences between baseline and pre‐ictal PSi. Results Eighty‐seven ECT sessions in 37 patients were analysed. Median baseline PSi was 94 (IQR 4) and pre‐ictal PSi was 38 (IQR 31; p < 0.001). No correlation was found between pre‐ictal PSi and EEG‐seizure duration. There were no significant effects of age or sex on pre‐ictal PSi while there was a significant difference between sexes on baseline PSi. Artefact and EMG activity in the EEG signal were minimal. Conclusion Pre‐ictal PSi was not associated with EEG‐seizure duration. Editorial Comment This study found no evidence to support a correlation between pre‐ictal Patient State index and seizure duration, thereby challenging any clinical utility for guiding ECT administration.