The delirium index, a measure of the severity of delirium: new findings on reliability, validity, and responsiveness.

OBJECTIVES

To assess the reliability, validity, and responsiveness of an instrument for measuring the severity of delirium, the Delirium Index (DI).

DESIGN

Prospective cohort study, with repeated patient assessments at multiple points in the hospital, at 8 weeks after discharge, and at 6 and 12 months after admission.

SETTING

The medical services of a primary acute-care hospital.

PARTICIPANTS

Medical admissions aged 65 and older: 165 with delirium and dementia, 57 with delirium only, 55 with dementia only, and 41 with neither.

MEASUREMENTS

Severity of delirium symptoms was measured using the DI. Delirium was diagnosed using the Confusion Assessment Method. Other measures included the Mini-Mental State Examination, Informant Questionnaire on Cognitive Decline in the Elderly, Barthel Index (BI), premorbid instrumental activities of daily living, Charlson Comorbidity Index, Clinical Severity of Illness scale (CSI), and the Acute Physiology Score (APS).

RESULTS

The intraclass correlation coefficient of interrater reliability was 0.98. Two measures of fluctuation were significantly higher in patients with delirium than in those without delirium. At baseline, the DI was correlated with the BI, APS, and CSI in delirious patients with (correlation coefficient (r)=-0.43, 0.17, and 0.36, respectively) or without (r=-0.44, 0.39, 0.22, respectively) dementia. At 8 weeks, in delirious patients with and without dementia, internal responsiveness as measured by effect sizes was -0.60 and -0.74, respectively, and the standardized response mean for both groups was -0.64. Low to good levels of external responsiveness were found.

CONCLUSION

The DI appears to be a reliable, valid, and responsive measure of the severity of delirium, in patients with delirium, with or without dementia.