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ICU hospitalization doubled the risk of subsequent dementia in older adults, a longitudinal study showed.

Compared with similar people who didn't have an ICU stay, older adults who had an ICU experience were more likely to develop all-type dementia (HR 2.20, 95% CI 1.75-2.77) or Alzheimer's dementia (HR 2.10, 95% 1.66-2.65), reported Bryan James, PhD, of Rush University in Chicago, at the 2022 Alzheimer's Association International Conference.

"ICU hospitalization due to critical illness has been linked to subsequent cognitive impairment in older patients; however, few studies have demonstrated that experiencing an ICU hospitalization is related to long-term risk of developing Alzheimer's and other age-related dementias," James told MedPage Today.

"Given the high rate of ICU hospitalization in older persons, especially during the COVID-19 pandemic, it's critical to explore this relationship," he added. "ICU hospitalizations may be an under-recognized risk factor for dementia in older adults."

Not all dementia comes on over a period of years, noted Wes Ely, MD, an ICU physician at Vanderbilt University Medical Center in Nashville, who wasn't involved with the study.

"What we've learned in the past decade is that there are millions of people who get an acquired dementia over a period of several weeks of acute injury during an illness, whether they're in the hospital or the ICU," Ely said.

"You don't have to be in an ICU on life support to get this, but just being critically ill, you can lose millions and millions of brain cells, and then weeks and months later have an ongoing problem with memory and executive function that on cognitive testing, looks basically like Alzheimer's disease," he told MedPage Today.

In some cases, post-ICU cognitive problems are fixable, Ely observed. "The brain is an extremely powerful tool and it's got a wonderful capacity for neuroplasticity," he said.

"Through cognitive rehabilitation and brain exercises -- whether it's Scrabble, Sudoku, or computerized brain games -- a lot of people find that they get dramatic improvements months and years later," he pointed out. "That's a ray of hope."

James and co-researchers studied 3,822 older adults in five diverse epidemiologic cohorts at the Rush Alzheimer's Disease Center without known dementia at enrollment. The cohorts were linked to Medicare claims data from 1991 to 2018.

Incident Alzheimer's and all-type dementia were assessed using standardized annual cognitive testing. Findings were adjusted for baseline measures of hypertension, diabetes, BMI, vascular risk factors, vascular disease burden, other chronic medical conditions, functional disabilities, depression, and physical activity.

Mean age of participants was about 73. Overall, participants were followed for an average of 7.8 years from study enrollment. About half of all participants (52.1%) had an ICU stay: 27% before they enrolled in a Rush study and 25.1% during follow-up.

The data sources did not allow the researchers to accurately assess delirium, James acknowledged. "But other research has shown that experiencing delirium in the ICU does lead to a higher risk for long-term cognitive impairment," he noted.

"This particular analysis was not designed to look at specific modifiable factors to reduce dementia risk for ICU patients, but we definitely plan to explore this in follow-up research," James added. Critical illness itself may harm the brain in some cases, he noted; for other patients, ICU events like sedation, severe sepsis, or acute dialysis may be contributing factors.

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