Risk factors for dementia after critical illness in elderly Medicare beneficiaries

Abstract

Introduction: Hospitalization increases the risk of a subsequent diagnosis of dementia. We aimed to identify diagnoses or events during a hospitalization requiring critical care that are associated with a subsequent dementia diagnosis in the elderly.

Methods: A cohort study of a random 5% sample of Medicare beneficiaries who received intensive care in 2005 and survived to hospital discharge, with three years of follow-up (through 2008) was conducted using Medicare claims files. We defined dementia using the International Classification of Diseases, 9th edition, clinical modification (ICD-9-CM) codes and excluded patients with any prior diagnosis of dementia or cognitive impairment in the year prior to admission. We used an extended Cox model to examine the association between diagnoses and events associated with the critical illness and a subsequent diagnosis of dementia, adjusting for known risk factors for dementia.

Results: Over the three years of follow-up, dementia was newly diagnosed in 4,519 (17.8%) of 25,368 patients who received intensive care and survived to hospital discharge. After accounting for known risk factors, having an infection (adjusted hazard ratio (AHR) = 1.25; 95% CI, 1.17 to 1.35), or a diagnosis of severe sepsis (AHR = 1.40; 95% CI, 1.28 to 1.53), acute neurologic dysfunction (AHR = 2.06; 95% CI, 1.72 to 2.46), and acute dialysis (AHR = 1.70; 95% CI, 1.30 to 2.23) were all independently associated with a subsequent diagnosis of dementia. No other measured ICU factors, such as need for mechanical ventilation, were independently associated.

Conclusions: Among ICU events, infection or severe sepsis, neurologic dysfunction, and acute dialysis were independently associated with a subsequent diagnosis of dementia. Patient prognostication, as well as future research into post-ICU cognitive decline, should focus on these higher-risk subgroups.

Figure 1

Flowchart of exclusions and final study cohort.

Figure 2

Cumulative incidence of all mortality and dementia for elderly ICU survivors over three years, adjusting for mortality as a competing risk. The dashed line is the cumulative incidence of all mortality during follow-up. The solid line is the cumulative incidence of dementia after adjusting for mortality as a competing event.

Figure 3

Cumulative incidence of dementia by five year age categories. Cumulative incidence of dementia, adjusted for mortality as a competing event, by age.

Figure 4

Cumulative incidence of dementia, stratified by (A) infection or severe sepsis, (B) acute neurologic dysfunction, (C) acute renal replacement therapy. Cumulative incidence (A. long dashed line is for infection, short dashed line is for severe sepsis, solid line is for no infection; B. dashed line is for neurologic dysfunction, solid line is for none; C. dashed line is for acute RRT, solid line is for none) of dementia after adjusting for mortality as a competing event. RRT, renal replacement therapy.