Delirium After Cardiac Surgery Predicts Cognitive Decline

Postoperative delirium might be associated with cognitive decline 4 to 6 weeks after cardiac surgery, a rigorous analysis has shown.

“The prevention of postoperative delirium may be a strategy for avoiding cognitive decline,” said lead investigator Charles Brown, MD, from the Johns Hopkins University School of Medicine in Baltimore.

Dr Brown pointed out that delirium occurs in about half of all patients after cardiac surgery and has been associated with profound long-term consequences, including cognitive decline and mortality. However, the actual risk is unclear because previous research has been limited by a lack of rigor in delirium assessment, the limited use of cognitive batteries, short follow-ups, and poor characterization of delirium and patient demographics.

In their study, the investigators used rigorous assessments and extensive psychometric batteries to determine whether delirium after cardiac surgery is associated with cognitive decline.

Dr Brown’s results from the study, which was part of an ongoing investigation of brain injury after cardiac surgery.

His team enrolled 66 patients who had undergone coronary artery bypass graft (CABG) or valve surgery involving cardiopulmonary bypass; all subjects were considered to be at high risk for neurologic injury.

Trained research assistants diagnosed postoperative delirium using the Confusion Assessment Method (CAM) or the CAM-ICU on 3 of the first 4 postoperative days. The CAM looks for acute onset and fluctuating course, inattention, disorganized thinking, and altered level of consciousness.

They determined severity with the Delirium Rating Scale-Revised-98. Psychometric testing was administered before surgery and 4 to 6 weeks after surgery. Multiple cognitive domains known to be affected by cardiac surgery were assessed with the Rey Auditory Verbal Learning Test, the Rey-Osterrieth Complex Figure Test, the Controlled Oral Word Association Test, the Symbol Digits Modalities Test, and the Trail Making Test, Part B.

Change in Z-score

The primary outcome was the change in composite cognitive Z-score from baseline. After adjustment for age, history of stroke, and cardiopulmonary bypass time, investigators determined the association between delirium and change in the composite cognitive Z-score.

Of the 66 patients enrolled, 35 (mean age, 69 years) underwent delirium assessments and full cognitive testing at baseline and at follow-up. Previous stroke was noted in 9.1% of participants.

Surgical procedures included CABG (51%), aortic or mitral valve surgery (34%), and a combination of the two (14%). Mean cardiopulmonary bypass time was 102 minutes.

The incidence of delirium in the study population was 48%, and the median delirium severity score was 5 (range, 2 – 9). Change in mean composite cognitive Z-score was better in patients without postoperative delirium than is those with postoperative delirium (+0.18 vs –0.11; P = .031).

“Patients with delirium had a decline from baseline,” Dr Brown reported.

After adjustment for age, history of stroke, and cardiopulmonary bypass time, the presence of postoperative delirium was still associated with a decrease in composite cognitive Z-score (–0.30; P = .04). Each increase in quartile of delirium severity was associated with 0.22 decrease in composite cognitive Z-score (P = .004)

“This is evidence of a potential dose effect,” he said. “More severe delirium indicated evidence of greater cognitive decline, and this was highly significant.”

This is evidence of a potential dose effect.

The investigators acknowledge that a larger cohort with a longer follow-up period is needed to confirm these results. “We are enrolling a larger population with longer follow-up,” Dr Brown reported, “looking for a subgroup of patients who may be most at risk.”

This team “has done a good job drawing attention to the importance of defining delirium after cardiac surgery, as well as summarizing the limitations of the findings in the study, said Kenneth Elmassian, DO, a specialist in cardiac anesthesia, vice chair of the Anesthesia Department at McLaren Greater Lansing, and immediate past-president of the Michigan State Medical Society.

“Importantly, they are taking a longer-term approach when assessing neurologic outcome. As far as drawing any conclusion on whether delirium after cardiac surgery is predictive of cognitive decline, I agree that a larger cohort would be helpful,” he said.

“We do know there are at-risk patients, especially the elderly and patients with evidence of previous neurologic injury or decline. But beyond preventive measures and techniques to limit any thromboembolic etiologies and eliminating the use of medications that might interfere with emergence from cardiac surgery, we are limited in our ability to totally prevent postoperative delirium or, for that matter, cognitive decline after cardiac surgery,” Dr Elmassian explained.