Detecting delirium superimposed on dementia: evaluation of the diagnostic performance of the Richmond agitation and sedation scale

Objectives—Delirium disproportionately affects patients with dementia and is associated with adverse outcomes. The diagnosis of delirium superimposed on dementia (DSD), however, can be challenging due to several factors including the absence of caregivers or the severity of pre-existing cognitive impairment. Altered level of consciousness has been advocated as a possible useful indicator of delirium in this population. Here we evaluated the performance of the Richmond Agitation and Sedation Scale (RASS) and the modified-RASS (m-RASS) – an ultra-brief measure of the level of consciousness – in the diagnosis of DSD. Design—Multicenter prospective observational study. RASS and m-RASS results were analysed together, labelled RASS/m-RASS). Setting—Acute geriatric wards, inhospital rehabilitation, emergency department. Participants—Patients 65 years and older with dementia. Measurements—Delirium was diagnosed with the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) or with the DRS-R-98 or with the 4AT. Dementia was detected with the Clinical Dementia Rating (CDR) Scale, the Short Form Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) or via the clinical records. Results—Of the 645 patients included, 376 (58%) had delirium. According to the instrument used to evaluate delirium the prevalence was 66% with the 4AT, 23% with the DSM and 100% with the DRS-R-98. Overall a RASS/m-RASS score other than 0 was 70.5% sensitive (95% CI: 65.9% – 75.1%) and 84.8% (CI: 80.5% – 89.1%) specific for DSD. Using a RASS/m-RASS value >+1 or <−1 as a cut-off, the sensitivity was 30.6% (CI: 25.9% – 35.2%) and the specificity was 95.5% (CI: 93.1% – 98.0%). The sensitivity and the specificity did not greatly vary according to the method of delirium diagnosis and the dementia ascertainment, though the specificity was slightly higher when the DSM and the IQCODE were used. Conclusion—In older patients admitted to different clinical settings the RASS and m-RASS analyzed as a single group had moderate sensitivity and very high specificity for the detection of DSD. Level of consciousness is therefore a valuable clinical indicator that should form part of delirium screening strategies, though for higher sensitivity other methods of assessment should be used.