A simplified 6-Item clinician administered dissociative symptom scale (CADSS-6) for monitoring dissociative effects of sub-anesthetic ketamine infusions

Background: Dissociation is a treatment-emergent adverse event commonly associated with IV ketamine, often measured using the 23-item Clinician-Administered Dissociative States Scale (CADSS). The objective of this study was to develop a short form version of the CADSS for easier clinical use. Methods: Retrospective data of 260 patients with treatment-resistant depression (TRD) receiving IV ketamine were randomly divided into two datasets. The first dataset (n = 130) was leveraged to develop a brief 6-item version of the CADSS (CADSS-6) based on items most sensitive to ketamine-induced dissociation. The CADSS-6 questions were then applied to the second dataset (n = 130) and the Spearman's correlation between the full-length CADSS and the CADSS-6 were assessed. Results: The CADSS-6 was developed from questions 1, 2, 6, 7, 15, and 22 from the full length CADSS. There was a strong significant correlation between the CADSS-6 total score and the CADSS total score at infusions 1 (rs(106) = 0.92, p < 0.001), 2 (rs(100) = 0.91, p < 0.001), 3(rs(99) = 0.95, p < 0.001) and 4 (rs(102) = 0.94, p < 0.001). Limitations: The CADSS-6 was developed using a retrospective data; therefore, the scale remains unvalidated in this population. Conclusions: The CADSS-6 presented herein was sensitive to dissociation experienced by patients receiving IV ketamine. Overall, the CADSS-6 was strongly correlated at each infusion with the full-length CADSS. While future studies should look to validate the CADSS-6 in a TRD sample, this scale offers clinicians a brief assessment that can be used to characterize symptoms of dissociation.