Acute psychoactive effects of intravenous ketamine during treatment of mood disorders: Analysis of the Clinician Administered Dissociative State Scale

Introduction: Ketamine has rapid-acting antidepressant effects. Frequently, ketamine administration also causes acute psychoactive effects - in trials, these effects are commonly measured using the Clinician Administered Dissociative State Scale (CADSS). However, the CADSS was not designed for this specific purpose, having been validated in other clinical contexts, and anecdotally does not appear to fully capture ketamine's acute psychoactive effects. Methods: Data were obtained from 110 individuals with mood disorders (predominantly major depressive disorder) who underwent intravenous ketamine infusion. An exploratory factor analysis (EFA) was performed on the CADSS, along with assessment of internal consistency. Qualitative methods were used to conduct in-depth interviews with a subset of these participants to identify key features of the acute ketamine experience, including aspects that may not be captured by the CADSS. Results: The mean total score of the CADSS was low at 7.7 (SD 9.2). Analysis of internal consistency showed a Cronbach's alpha of 0.74. Five CADSS items had low correlations with the total score. EFA lead to a one-factor solution containing 16 items. Five of the six highest loading items involved perceptual disturbances, either of time or sensation. Qualitative analyses of 10 patient narratives revealed two phenomena not captured on the CADSS: disinhibition and a sense of peace. Limitations: This study was by limited by the absence of other ratings of the participants' experience. Conclusion: Findings suggest that the CADSS partially captures the acute effects of ketamine administration. Further research may seek to validate a revised version of the CADSS that more accurately measures these effects.