In the days just after a cardiac operation, older patients often experience a decline in cognitive function, such as memory problems or an inability to focus. Although these problems are usually temporary, a large number of these patients will experience long-term cognitive difficulties, lasting as long as a year after surgery. It is unknown why this happens.
New research published in The New England Journal of Medicine explains the link between postoperative delirium and an extended loss of cognitive function in cardiac surgery patients.
Delirium is a state of confusion that can develop following illness, infection or surgery, and is one of the most common complications in hospitalized patients over age 65.
The new findings suggest that interventions to prevent delirium before surgery takes place could help cardiac patients avoid long-term cognitive problems.
“Our findings now suggest that postoperative delirium, once thought of as an acute, transient cognitive disorder, may have longer-term effects on cognitive function in patients undergoing cardiac surgery,” said co-lead author Jane Saczynski, PhD, assistant professor of medicine at the University of Massachusetts Medical School.
Delirium has been studied quite extensively in other patient populations, such as general medical and surgical patients and orthopedic surgery patients; however, few delirium studies have focused on cardiac surgery patients.
“With the aging of the patient population undergoing cardiac surgery and increases in survival after surgery, clinicians and patients are increasingly concerned with factors associated with quality of life, including cognitive status, as major outcomes of surgery,” say the authors.
“Whether postoperative delirium is associated with prolonged cognitive dysfunction has been unclear.”
For the study, researchers followed for one year post-surgery 225 patients ages 60 to 90. Patients had undergone either coronary artery bypass grafting (CABG) or heart valve replacement surgery and were assessed for both delirium and cognitive impairment.
“One of the real strengths of our study is that we assessed patients’ cognitive function preoperatively and an average of five times during the year after surgery,” said co-lead author Edward Marcantonio, MD, section chief for research in BIDMC’s Division of General Medicine and Primary Care and professor of medicine at Harvard Medical School.
“Previous research had shown an association between postoperative delirium and functional decline in activities of daily living. But, believe it or not, the one thing that’s been most uncertain is the association between delirium and long-term cognitive difficulties. This study allowed us to accurately model the course of cognitive function and to compare the rate of recovery among patients with and without postoperative delirium,” he added.
The findings show that compared with patients who did not experience delirium, the 103 patients who developed delirium after cardiac surgery (46 percent of the total) experienced a more significant drop in cognitive performance immediately following surgery, as determined by the Mini-Mental State Examination (MMSE).
They also took much longer to recover back to pre-surgical functioning than did patients who did not develop delirium. For example, five days after surgery, almost half of the patients who did not develop delirium returned to their original cognitive levels while less than 20 percent of those with delirium returned to pre-operative level of function.
Furthermore, six months after surgery, over three-fourths of those without delirium had recovered cognitively compared to only 60 percent of those with delirium.
These results suggest that identifying patients at high risk for delirium before surgery and promoting interventions to prevent delirium in cardiac surgical patients may have substantial benefits. It could improve the recovery rate of cognitive abilities and enhance functional recovery following surgery.
“Since patients who experience delirium continue to show improvement in cognitive function six months after surgery, extending additional rehabilitation services to these patients may have added benefits,” said co-senior author Richard N. Jones, ScD, director of mental health and aging at Hebrew SeniorLife and assistant professor of medicine at Harvard Medical School.
Further cognitive screening at discharge may also identify patients who need closer, post-operative monitoring or specific transitional care to aid in the return of cognitive functions.
“More than half a million heart surgeries are performed each year,” added Marcantonio. “Our findings provide important information that might help doctors design interventions to improve the outcomes of older adults undergoing cardiac surgeries.”