EEG Delirium Index as a diagnostic screening biomarker in hospitalized nonagenarians: a preliminary validation study

BACKGROUND Quality delirium care depends on monitoring and early identification. This is especially true among older adults, who are at highest risk for delirium. The electroencephalography-based delirium index (EEG-DI) is robustly associated with delirium among critically ill adults, and may contribute to improved monitoring. Yet neurophysiologic changes with aging or dementia could impact its performance. OBJECTIVE We examined the performance of the EEG-DI in a cohort of hospitalized nonagenarians, who have increased rates of dementia. We hypothesized that, consistent with prior work, delirium is associated with lower EEG-DI values, even after adjusting for history of dementia. METHODS In this retrospective observational study, we identified hospitalized patients over 90 years of age, with EEGs recorded for clinical purposes between May 2014 and January 2020. We obtained clinical and demographic data from the electronic health record. We computed EEG-DI as previously published, based on frequency composition and variability of the raw EEG signals. We used multivariable logistic regression to model the relationship between EEG-DI and presence of delirium, adjusting for confounders including dementia history. We used receiver operating characteristic (ROC) analysis to evaluate EEG-DI performance in patients with and without dementia. RESULTS The final analysis included 68 nonagenarians (mean age 92 years; 42 [62%] women), of whom 22 (33%) had dementia and 32 (47%) had delirium. Lower EEG-DI was independently associated with greater likelihood of delirium (adjusted odds ratio [aOR] 11.2, 95% CI 2.0-62.4, p=0.006). Optimism-corrected area under the ROC curve for delirium was 0.80 (95% CI 0.68-0.93) in patients without dementia and 0.65 (95%CI 0.32 to 0.90) with dementia. CONCLUSION Lower EEG-DI is strongly associated with delirium in nonagenarians, similar to the association reported in younger patients. EEG-DI showed poor discrimination for delirium in patients with dementia and may not be appropriate for use in this population.