Hospitalization Associated With Cognitive Decline in Elderly Patients

Deborah Brauser

February 25, 2010

February 25, 2010 — Older individuals hospitalized for acute care or a critical illness are more likely to experience cognitive decline, new research suggests. In addition, individuals hospitalized with a noncritical illness were also more likely to develop incident dementia, new research suggests.

"This is the first study to our knowledge to find [this] association," write William J. Ehlenbach, MD, MSc, Department of Pulmonary and Critical Care Medicine at the University of Washington in Seattle, and colleagues.

Although the mechanisms are uncertain, the researchers speculate that hypoxemia, delirium, hypotension, glucose dysregulation, systemic inflammation, and sedative and analgesic medications may all have a role to play. In addition, the study authors note that hospitalization may be a marker for cognitive decline or dementia that has previously gone undiagnosed.

"We know that older individuals are at higher risk for critically ill hospitalizations, and we also know that as people live longer with chronic disease, the incidence of critical illness increases," Dr. Ehlenbach told Medscape Psychiatry. "I think it's important that we understand the impact that this has and understand what the outcomes are for 'the lucky ones,' the ones who survive and get better from such an illness."

This understanding could then lead to future research to better understand the underlying mechanisms. "We have to really understand the problem before we can learn how to prevent and treat it," he said.

This study is published in the February 24 issue of the Journal of the American Medical Association.

Lower CASI Scores

Although past studies have suggested that critical illness survivors may experience some long-term cognitive impairment, premorbid measures of cognitive functioning and the risk for dementia associated with critical illness have not been evaluated.

"We wanted to determine whether a decline in cognitive function was greater among older individuals who experienced hospitalizations relative to those not hospitalized and to determine whether the risk for incident dementia differed by these exposures," said Dr. Ehlenbach.

His team evaluated data from a random sample of 2929 participants without dementia at baseline from the ongoing Adult Changes in Thought trial, a population-based, longitudinal study on aging and dementia. All participants in this analysis were from the Seattle area, were older than 65 years, and did not reside in a nursing home.

At baseline, participants completed questionnaires on demographics, medical history, and general functioning and were evaluated with the Cognitive Abilities Screening Instrument (CASI). At each 2-year follow-up visit, the participants were again screened by CASI, and those scoring less than 86 were given a clinical evaluation for dementia.

After a mean follow-up of 6.1 years, the investigators found that 1601 of the participants had not experienced any hospitalizations, whereas 1287 had 1 or more hospitalizations for noncritical illnesses and 41 had 1 or more for illnesses that were critical.

The adjusted CASI scores "averaged 1.01 points lower for visits following acute care illness hospitalization compared with follow-up visits not following any hospitalization (P < .001) and 2.14 points lower on average for visits following critical illness hospitalization (P = .047)," the investigators report.

The numbers of dementia cases found were 146, 228, and 5 for those not hospitalized, those with noncritical hospitalizations, and those with critical hospitalizations, respectively. The adjusted hazard ratio for incident dementia was 1.4 following a noncritical hospitalization (95% confidence interval [CI], 1.1 – 1.7; P = .001) and 2.3 after a critical hospitalization (95% CI, 0.9 – 5.7; P = .09).

"While critical illness hospitalization and incident dementia were not statistically significantly associated, this comparison had low power to detect a difference," the study authors write.

Understanding the association between critical illness and neurocognitive impairment has the potential to improve the overall care of critically ill patients. "Establishing that an association exists will help direct research at the contributing factors behind the association or guide the creation of specific rehabilitation programs for these patients."

Limitations of the study included the reliance on administrative data, the substantial interval between study visits, and the low number of individuals who experienced a critical illness hospitalization. "This lack of power prevented exploration of specific critical illness syndromes and cognitive decline," the study authors write.

"I think that, like many studies, this one raises additional important questions, but I think it does lay out future directions for research," said Dr. Ehlenbach.

"I also think the important message for clinicians is that they should be aware of this issue, and it should be on their radar. When seeing older patients that have survived critical illness or have recently been hospitalized, these patients should be evaluated for cognitive impairment."

Hospitalize Only if Absolutely Necessary

"This is the largest study ever of its type to show these correlations," George T. Grossberg, MD, professor and director of geriatric psychiatry in the Department of Neurology and Psychiatry, Saint Louis University School of Medicine, Missouri, told Medscape Psychiatry.

"I don't think the findings are surprising, but they are important in that they reconfirm that when you're dealing with older adults, putting them in a complex and very stressful environment such as a hospital can lead to an acceleration in their cognitive decline," said Dr. Grossberg, who was not involved with this study.

"For the practicing clinician, I think the takeaway message is that if you have a practice that has older adults, particularly over the age of 65, if you don't have to hospitalize them, then don't hospitalize," he added. "Try to keep them out of the hospital if at all possible. Also, you should always be measuring cognitive baselines before patients get hospitalized and then follow them cognitively afterwards."

He noted that cognition should be measured during hospitalizations just as are the typical vital signs of blood pressure, temperature, pulse, respiration, and sometimes pain. "I think we should think of cognition as maybe the sixth vital sign for older individuals."

This study was funded by a National Institute of Health (NIH) National Institute on Aging Cooperative Grant; an NIH Respiratory Research Training Grant; the John A. Hartford Foundation; a K24 award from the National Heart, Lung, and Blood Institute; and a Department of Veterans Affairs Health Services Research and Development Postdoctoral Fellowship. The study authors and Dr. Grossberg have disclosed no relevant financial relationships.

JAMA. 2010;303:763-770.