The Better Assessment of Illness Study for Delirium Severity: Study Design, Procedures, and Cohort Description

Background/Objectives: To describe the design, procedures, and cohort for the Better ASsessment of ILlness -(BASIL) study, which is conducted to develop and test new delirium severity measures, compare them with existing measures, and examine related clinical outcomes. Methods: Prospective cohort study with 1 year follow-up of study participants at a large teaching hospital in Boston, Massachusetts. After brief cognitive testing and the Delirium Symptom Interview, delirium and delirium severity were rated daily in the hospital using the Confusion Assessment Method (CAM) and CAM-Severity score, the Delirium Rating Scale-Revised-98 (DRS-R-98), and the Memorial Delirium Assessment Scale (MDAS). Other key study variables included comorbidity, physical function (basic and instrumental activities of daily living [ADL]), ratings of subjective health and well-being, and clinical outcomes (length of stay, 30 day rehospitalization, nursing home admission, healthcare utilization). Follow-up interviews occurred at 1- and 12-month with patients and families. In 42 patient interviews, inter-rater reliability for key variables was assessed. Results: Of 768 eligible patients approached, 469 were screened and 352 enrolled, yielding an overall study response rate of 67% for potentially eligible participants. The mean participant was 80.3 years old (SD 6.8) and 203 (58%) were female. The majority of patients were medically complex with Charlson Comorbidity Scores ≥2 (192 patients, 55%), and 102 (29%) met criteria for dementia. Inter-rater reliability assessments (n = 42 pairs) were high for overall ratings of presence or absence of delirium by CAM (κ = 1.0), delirium severity by DRS-R-98 and MDAS (weighted kappa, κ = 1.0 for each) and for ADL impairment (κ = 1.0). For eligible participants at each time point, 278 out of 308 (90%) completed the 1-month follow-up and 132 out of 256 (53%) have completed the 12-month follow-up to date, which is still in progress. Among those who completed interviews, there was only 1-3% missing data on most major outcomes (delirium, basic ADL, and readmission). Conclusion: The BASIL study presents an innovative effort to advance the conceptualization and measurement of delirium severity. Unique strengths include the diverse cohort with complete high quality data and longitudinal follow-up, along with detailed collection of multiple delirium measures daily during hospitalization.