The effect of anaesthetic dose on response and remission in electroconvulsive therapy for major depressive disorder: nationwide register-based cohort study

BACKGROUND: Electroconvulsive therapy (ECT) is a safe and effective treatment for major depressive disorder (MDD). ECT treatment effect relies on induced generalised seizures. Most anaesthetics raise the seizure threshold and shorten seizure duration. There are no conclusive studies on the effect of anaesthetic dose on response and remission rates with ECT for MDD. AIMS: We aimed to examine the effect of different dose intervals of anaesthetics on response and remission after ECT for MDD. METHOD: We conducted a nationwide cohort study, using data from Swedish registers. Low-, medium- and high-dose intervals, adjusted for age and gender, were constructed for each anaesthetic drug. Response and remission were measured with the Clinical Global Impression – Severity and Improvement scales (CGI-I and CGI-S), and a self-rated version of the Montgomery–Åsberg Depression Rating Scale (MADRS-S). Logistic regression models were used to calculate adjusted odds ratios for response and remission rates. RESULTS: The study included 7917 patients who received ECT for MDD during 2012–2018. Patients were given either thiopental (64.1%) or propofol (35.9%). Low-dose intervals of anaesthetics were associated with increased rates of response (CGI-I: odds ratio 1.22, 95% CI 1.07–1.40, P = 0.004; MADRS-S: odds ratio 1.31, 95% CI 1.09–1.56, P = 0.004) and remission (CGI-S: odds ratio 1.37, 95% CI 1.17–1.60, P ≤ 0.001; MADRS-S: odds ratio 1.31, 95% CI 1.10–1.54, P = 0.002). CONCLUSIONS: We found improved treatment outcomes with low- compared with high-dose anaesthetic during ECT for MDD. To enhance treatment effect, deep anaesthesia during ECT for MDD should be avoided.