Postoperative delirium has lasting cognitive consequences

Jul 10 2012

By Eleanor McDermid

Patients may take a long time to recover from the cognitive impact of cardiac surgery if they develop postoperative delirium, research shows.

This was particularly marked among patients with delirium lasting more than 3 days, report Jane Saczynski (University of Massachusetts Medical School, Worcester, USA) and team.

"Our findings are of clinical significance, since the risk of delirium among patients undergoing cardiac surgery can be predicted preoperatively, and delirium is potentially preventable," they write in TheNew England Journal of Medicine.

"Identifying patients at high risk for delirium and promoting the development of interventions to prevent delirium in patients undergoing cardiac surgery may reduce the rate of long-term cognitive impairment in this population."

Postoperative delirium was common in the current study, affecting 46% of 225 patients (average age 73 years). The researchers used the Confusion Assessment Method to diagnose delirium, which they say is "the most widely adopted, validated approach in the literature."

Patients with postoperative delirium had significantly poorer preoperative cognition than patients without, with Mini-Mental State Examination (MMSE) scores of 25.8 versus 26.9 (absolute difference of 1.1 points), adjusted for variables including age and history of stroke.

They also had a much larger decline in cognition at 2 days after surgery, with MMSE scores falling by 7.7 points compared with 2.1 points in patients without delirium. The fall was largest in patients whose delirium lasted longer than 3 days.

Patients with delirium made faster recoveries between postoperative days 3 and 5 than those without, but the absolute difference between MMSE scores, of 3.3 points, was still significant and larger than at baseline.

This difference was still present at 30 days after surgery, and patients whose delirium lasted longer than 3 days made particularly slow recoveries over this period.

Over the next 5 months, patients with postoperative delirium made larger cognitive gains than the other patients, and the 2.0-point difference in MMSE scores at 6 months was not significant. However, significantly more patients with than without delirium had not regained their preoperative level of cognitive function at this point, at 40% versus 24%.

One year after surgery, 31% and 20% of patients with and without postoperative delirium had regained their previous level of cognitive function. The difference was not significant.

"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," say Saczynski et al.

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