FRIDAY, Sept. 29, 2023 (HealthDay News) -- Delirium is common after older patients have surgery and can cause serious complications and distress, but its cause has been a mystery.

New research has found that patients who develop postoperative delirium have increased openings in the blood-brain barrier, the layer of cells that prevent substances from entering the brain.

“These findings are significant because we now have a road map to tackle a problem that impacts millions of older adults in the U.S. every year,” said study author Dr. Michael Devinney, an assistant professor of anesthesiology at Duke University School of Medicine in Durham, N.C.

“If we can find a way to prevent the blood-brain barrier from opening after surgery or figure out what is passing through this barrier and getting to the brain, we can work to develop a therapy that may prevent postoperative delirium,” he said in a university news release.

Up to 40% of older surgery patients have postoperative delirium, a type of confusion that happens in the first few days after surgery. It is associated with longer hospitalizations, significant distress and major post-op complications.

Past studies in mice have also found that this may be caused by disruptions of the blood-brain barrier.

The new study also found that patients who had lower performance on tests of memory and thinking skills before surgery were more likely to experience post-op delirium.

Scientists studied this in more than 200 patients age 60 and up before and after their non-cardiac and non-neurological surgeries.

Researchers collected spinal fluid and blood samples before surgery and 24 hours after. They measured the ratio of a protein called albumin as an indicator of the barrier’s fluidity.

Study participants also completed extensive cognitive evaluations before and after surgery.

The study found that permeability of the blood-brain barrier was associated with greater rates of delirium and longer hospital stays in all patients.

Researchers said this suggests the increase in permeability is a response to surgery.

Poorer performance on the cognitive tests separately affected delirium risk, according to the study.

“Our work suggests that there may be a two-hit model for postoperative delirium,” Devinney said. “It appears to involve both a predisposing factor such as impaired preoperative cognition, and a precipitating factor involving postoperative blood-brain barrier dysfunction.”

It’s known that inflammatory molecules can pass through a leaky blood-brain barrier and cause cognitive impairments.

Researchers plan to follow this study with a closer look at the collected spinal fluid samples to see if patients who experienced delirium have higher levels of particular inflammatory factors.

The findings were published recently in Annals of Neurology. The U.S. National Institutes of Health was among the organizations that funded the study.

More information

The American Medical Association has more on post-operative delirium.

SOURCE: Duke Health News, news release, Sept. 27, 2023