Predictors of Delirium Development in Older Medical Inpatients: Readily Identifiable Factors at Admission

Niamh A O'Regan, James Fitzgerald, Dimitrios Adamis, David William Molloy, David Meagher, Suzanne Timmons

Identifying patients at high risk of delirium is crucial to facilitate prevention. Although dementia is the most consistent risk factor across populations, it remains under-diagnosed. Hence understanding other markers of delirium vulnerability on admission is important. We aimed to identify predictors of incident delirium development in older medical inpatients that were readily identifiable at presentation to the emergency department. Medical inpatients of ≥70 years were assessed on admission for delirium using the Revised Delirium Rating Scale (DRS-R98) and those with prevalent delirium were excluded. Consenting non-delirious patients were then assessed daily using the DRS-R98. Data pertaining to multiple baseline delirium risk factors were collected, including pre-morbid dementia. Multivariable logistic regression was used to examine which factors predicted the development of incident delirium. Of 555 patients approached, 184 (33.1%) had prevalent delirium. Following other exclusions, 191 were included in the study and 61 developed incident delirium. Predictors of incident delirium on multivariable analysis, controlling for confounders, were dementia (OR 2.54, 95% CI 1.01-6.43, p = 0.048); Barthel Index score (OR 1.15 for each unit decrease in score, 95% CI 1.06-1.25, p = 0.001), and Modified Cumulative Illness Rating Scale score (OR 1.13 for each unit increase in score, 95% CI 1.05-1.22, p = 0.001). Dementia is a well-known risk factor for delirium; however, it too is under-recognized and on admission can be missed. Conversely, the Barthel Index is a simple and widely used measure of functional ability that may prove useful in stratifying those at risk of in-hospital delirium on admission.