Risk of a Diagnosis of Dementia for Elderly Medicare Beneficiaries after Intensive Care

Abstract

Abstract Background Critical illness is likely associated with an increased risk of dementia, but the magnitude remains uncertain. Methods The cohort was a random 2.5% sample of Medicare beneficiaries who received intensive care in 2005 and survived to hospital discharge. Patients were matched with general population controls (age, sex, and race) with 3 yr of follow-up. The authors used an extended Cox model to assess the risk of a diagnosis of dementia, adjusting for the known risk factors for dementia, and the competing risk of death. Results Among 10,348 intensive care patients who survived to hospital discharge, dementia was newly diagnosed in 1,648 (15.0%) over the 3 yr of follow-up versus 12.2% in controls (incidence per 1,000 person-years, 73.6; 95% CI, 70.0 to 77.1 vs. 45.8; 95% CI, 43.2 to 48.3; hazard ratio [HR], 1.61; 95% CI, 1.50 to 1.74; P < 0.001). After accounting for the known risk factors in the year before the index hospitalization, the risk of receiving a diagnosis of dementia remained increased in patients who received intensive care (adjusted HR, 1.43; 95% CI, 1.32 to 1.54; P < 0.001). Inclusion of identifiable risk factors accrued during the quarter of critical illness accounted for almost all of the increased risks (adjusted HR, 1.09; 95% CI, 1.00 to 1.20; P = 0.06). Conclusions Elderly critical care survivors have a 60% increased relative risk, but only 3% increased absolute risk, of receiving a diagnosis of dementia in the subsequent 3 yr compared with the general population. This increased risk is not accounted for by risk factors preexisting the critical illness. Surveillance bias, which increases the likelihood of receiving a diagnosis of dementia, could account for some or all of these additional risks.