Postop Delirium Tied to Long-term Cognitive Impairment

Megan Brooks

July 05, 2012

July 5, 2012 — Patients who develop delirium after cardiac surgery often experience a sudden decline in cognitive function immediately after surgery, with lingering impairment during the following year, results of a prospective study suggest.

"These findings suggest that delirium, which was once thought of as a short-term, transient cognitive disorder, may have longer-term observed effects on cognitive function in patients who have undergone cardiac surgery," the study team notes.

Jane S. Saczynski, PhD, from the University of Massachusetts Medical School in Wooster, co–first author of the article, with Edward R. Marcantonio, MD, of Beth Israel Deaconess Medical Center and Hebrew Senior Life, in Boston, told Medscape Medical News that their observations have several clinical implications.

Dr. Jane Saczynski

First, "more attention needs to be paid to delirium, which very often goes undiagnosed, and cognitive status during hospitalization and especially after surgery," she said. "There are known risk factors for delirium in patients undergoing cardiac surgery (eg, preexisting cognitive impairment, history of depression, history of stroke) and also preventive measures that can be taken to help prevent the development of delirium."

"In patients who do develop delirium, closer monitoring after discharge may be necessary, and rehabilitation services may need to be extended since cognitive status continues to improve through 6 months after surgery, when many rehab services have ended," Dr. Saczynski added.

Their results are published in the July 5 issue of the New England Journal of Medicine.

Prevention Important

The study involved 225 patients aged 60 years and older who were scheduled for coronary-artery bypass graft surgery or valve replacement. Patients were assessed for relevant outcomes preoperatively, daily during hospitalization beginning on postoperative day 2, and at 1, 6, and 12 months after surgery.

A total of 103 patients (46%) developed delirium postoperatively; these patients had lower preoperative mean Mini-Mental State Examination (MMSE) scores than those without delirium (25.8 vs 26.9, P < .001).

In adjusted models, patients with delirium had a larger decline in cognitive function as assessed using the MMSE 2 days after surgery than did those without delirium (7.7 points vs 2.1, P < .001). They also had significantly lower postoperative cognitive function than those without delirium, both at 1 month (mean MMSE score, 24.1 vs 27.4; P < .001) and at 1 year (25.2 vs 27.2, P < .001) after surgery.

After adjusting for baseline differences, the between-group difference in mean MMSE scores was significant 30 days after surgery (P < .001) but not at 6 or 12 months (P = .056 for both), the researchers report.

They also report that a higher percentage of patients with delirium than without delirium had not returned to their preoperative baseline level of cognitive function at 6 months (40% vs 24%, P = .01), but the difference was not significant at 12 months (31% vs 20%, P = .055).

"Our study," Dr. Saczynski told Medscape Medical News, "adds to the body of literature on the association between delirium and cognitive function after cardiac surgery by establishing a link between postoperative delirium and long-term cognitive impairment (up to a year after surgery). We used state-of-the-art assessments of delirium and were also able to assess cognitive function prior to surgery — both of which have been lacking in previous studies," she noted.

Co–senior authors of the article are Sharon K. Inouye, MD, MPH, and Richard N. Jones, ScD, both from Beth Israel Deaconess Medical Center and Harvard Medical School.

Novel Study, Confirmatory Data

Timothy Girard, MD, from Vanderbilt University School of Medicine in Nashville, Tennessee, who was not involved in the study, said, "Taken broadly, this important study confirms the findings of earlier studies showing that patients who become delirious in the hospital (eg, after surgery, in the ICU, or on the medical ward) have worse cognitive outcomes months later than patients who do not become delirious."

"The novel aspect of the study by Sacyznski and colleagues is their careful methodology, which represents a significant advance in this field," Dr. Girard said.

"They assessed patients' cognitive function not just once after surgery but before surgery and multiple times after surgery, which allowed them to compare trajectories of change in cognition over a long period of time among those with vs without postoperative delirium."

Dr. Girard agrees that postoperative delirium, and delirium in general, should receive more attention.

"Specifically, this study suggests that efforts to prevent, monitor, and treat delirium after cardiac surgery could improve cognitive outcomes not only during the short period after surgery but also potentially during the months to years following surgery," he said.

The study was supported by the Harvard Older Americans Independence Center, the National Institute on Aging, and the National Heart, Lung and Blood Institute. The authors and Dr. Girard have disclosed no relevant financial relationships.

N Engl J Med. 2012;367:30-39. Abstract

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