Effects of Low-dose Ketamine as an Adjunct to Propofol-based Anesthesia for Electroconvulsive Therapy

Inclusion Criteria: * referred for ECT with a Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) diagnosis of major depressive disorder * considered American Society of Anesthesiologists (ASA) Physical Class I - III * baseline MADRS score greater than 24 (i.e. at least moderate to severe depression) * a "first" or "new" episode of depression which has lasted not more than 3 months and requires ECT treatment as judged by a psychiatrist Exclusion Criteria: * ASA Class IV or V as judged by the anesthesiologist * Any ECT treatment in the previous three months * Inability or refusal to provide informed consent * A history of allergic reactions, hypersensitivity, or intolerance to anesthetics or their constituents used in the study (ketamine, propofol, egg phosphatide, soybean oil) * Anyone taking medications considered contraindicated for ECT or for general anesthesia * Presence of any of the following DSM-IV diagnoses: Substance or alcohol dependence at enrolment (except dependence in full remission, and except for caffeine or nicotine dependence), abuse of opiates, amphetamines, barbiturates, cocaine, cannabis, or hallucinogen abuse in the 4 weeks prior to enrolment, pervasive developmental disorder, dementia * Significant medical condition that would contraindicate the use of ketamine, propofol or that is untreated and would need urgent attention (as determined by treating physician) * Medical conditions that would significantly affect absorption, distribution, metabolism, or excretion of ketamine or propofol * Unstable or inadequately treated medical illness (e.g. congestive heart failure, angina pectoris, hypertension) as judged by the investigator * Patients with increased risk of laryngospasm (such as active pulmonary infection, upper respiratory infection, asthma), increased intracranial pressure, glaucoma, thyroid disease/hyperthyroidism * Any clinically significant deviation from the reference range in clinical laboratory test results as judged by the investigator * Pregnancy (or female of child-bearing age not using adequate contraception) or lactation * Participation in another drug trial within 4 weeks prior enrolment into this study or longer in accordance with local requirements