Acute kidney injury might diminish cognition

Patients who sustain an acute kidney injury during a hospital stay due to a heart or lung condition face the risk of reduced mental acuity — even years later. This finding emerged in a study published this month in the Clinical Journal of the American Society of Nephrology.

The UW Medicine-led study followed 1,538 patients for three years. Participants underwent cognitive tests at intervals of three, 12 and 36 months after their hospitalizations.

“For the last two or three decades, there has been a growing recognition and concern of the long-term physical and cognitive consequences after hospitalization,” said lead author Dr. Pavan Bhatraju, associate professor (Pulmonary, Critical Care and Sleep Medicine). 

“Caring for patients in the hospital, we have noticed some patients have declines in cognitive function after leaving the hospital and we were wondering why this happens,” he said. 

Bhatraju and colleagues wondered if acute kidney injury might be a risk factor because kidneys were not effectively clearing toxins from the body, a situation that might result in an inflammatory reaction in the brain, he said.

Acute kidney injury sometimes occurs in patients whose hospitalization is related to cardiac surgery, respiratory failure or pneumonia. 

The researchers' main finding was that hospitalized patients who develop acute kidney injury, especially if they are elderly, are at an increased risk of long-term cognitive decline, Bhatraju said. 

“We know that it happens,” he said. “Now we want to know why it occurs and how to prevent it.”

Those questions will likely be the topic of continuing research, he said. 

The researchers studied inpatients at UW Medicine, Vanderbilt University, Kaiser Permanente and Yale University. Of the 1,500 in the original cohort, about 1,400 returned for follow-up cognitive tests for the next three years. Among those people, half had a history of acute kidney injury and half did not. The patients' mean age was 65 years. 

Researchers also tested for a biomarker that appeared when inflammation was discovered in the body, and found significantly higher levels of this biomarker in patients who had an acute kidney injury. 

Cognitive tests showed a small but marked decline in cognition for those patients who had sustained an acute kidney injury. In the tests, participants could score 0 to 100. The average score for a patient without an acute kidney injury was 92-93. Patients with acute kidney injury typically had scores two to five points lower. Scores below 85 triggered a dementia screening. 

There are no effective therapeutics to prevent this cognitive loss, he said.

The numbers do not definitively link acute kidney injury with severe loss of cognitive function or dementia, he said. But it will lead researchers to focus more on how to prevent and treat cognitive decline after such an event. 

“We don’t know for certain that AKI can lead to brain dysfunction,” he said. “That is what we want to study next.”

The ASSESS-AKI was supported by cooperative agreements from the National Institute of Diabetes and Digestive and Kidney Diseases (U01DK082223, U01DK082185, U01DK082192, and U01DK082183) and funding from National Institutes of Health (R01HL085757, R01DK098233, R01DK101507, R01DK114014, K23DK100468, R03DK111881, R01DK093771, K01DK120783, P30DK079310, P30DK114809, and K23DK116967 and R01DK133177).