Delirium increases risk of cognitive dysfunction, but only in the first postoperative month

New research indicates that older patients who develop delirium- an acute attentional deficit that waxes and wanes, right after surgery are more likely to show signs of postoperative cognitive dysfunction one month later. But the study, published in the Online First edition of Anesthesiology, the peer-reviewed medical journal of the American Society of Anesthesiologists (ASA), also found that the number of patients still showing signs of postoperative cognitive dysfunction decreased steadily and significantly at two and six months after surgery.

Delirium is a common postoperative complication in older surgical patients and has been associated with cognitive decline, increased risk of dementia, and a host of other negative outcomes. Additionally, delayed or incomplete cognitive recovery can complicate recuperation for older surgical patients. When cognitive impairment following surgery lasts for more than 3 months, it is known as postoperative cognitive dysfunction.

The main finding of this study was that delirium significantly increased the risk of postoperative cognitive dysfunction, but primarily in the first postoperative month. For a substantial number of people, 'brain healing' will continue long after hospital discharge. This delayed neurocognitive recovery may represent a normal response to the waning effects of surgery, anesthesia, pain, and medications. Our findings indicate that these effects are short-lived for most older adults."

Study lead author Lori Daiello, PharmD, assistant professor of neurology at the Warren Alpert Medical School of Brown University in Providence, Rhode Island

Researchers used data from the Successful Aging after Elective Surgery (SAGES) study, which examined the long-term impact of delirium on postoperative cognitive functioning among 560 older adult surgical patients, over the age of 70. The average age patient was 77 years. SAGES participants were given tests of memory and thinking shortly before and after surgery. They were also tested at follow-up visits one, two, and six months after surgery. Sharon Inouye, M.D., professor of medicine at Harvard Medical School, is the overall principal investigator of the SAGES study, which is funded by a grant from the National Institute on Aging. She, along with Richard Jones, M.D., from Brown University, were co-senior authors on this study.

Nearly one quarter (24%) of patients developed in-hospital delirium after surgery. One month later, nearly half of patients (47%) had not recovered their pre-surgical cognitive abilities and met the criteria for postoperative cognitive dysfunction. This was the only time at which the authors found a statistically significant association between postoperative delirium and postoperative cognitive dysfunction.

Fewer patients qualified as having postoperative cognitive dysfunction at 2 months (23%) and 6 months (16%) after surgery. At each evaluation, postoperative cognitive dysfunction was more common among patients who had not experience postoperative delirium.

Dr. Daiello notes that the study findings suggest that postoperative delirium and postoperative cognitive dysfunction may be distinct manifestations of perioperative neurocognitive dysfunction. As the relationship between delirium and postoperative cognitive dysfunction becomes better understood, future research can examine the underlying mechanisms in the hope of developing strategies to prevent these conditions.

In an accompanying editorial, Jeff Browndyke, Ph.D., Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, notes that "the study reveals the difficulties inherent in ascertaining what is 'meaningful' postoperative cognitive change and reminds us that often the devil is in the details. The study also suggests that delirium and POCD are distinct clinical entities, for which differential clinical management will be needed to guide anesthesiologists as we move forward to optimize perioperative brain health."

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