ARTICLE IN BRIEF
Up to one year after undergoing cardiac surgery, 46 percent of 225 cardiac surgery patients who were diagnosed with post-operative delirium were less likely to return to their baseline level of cognitive function. Experts discuss how to interpret the findings and possible interventional strategies.
Delirium, a widely recognized complication in older patients who undergo cardiac surgery, is often considered to be a temporary state. But a new study in the July 5 issue of New England Journal of Medicine suggests that delirium may result in long-term cognitive decline for these patients.
Up to one year after undergoing cardiac surgery, 46 percent of 225 cardiac surgery patients who were diagnosed with post-operative delirium were less likely to return to their baseline level of function, investigators from the University of Massachusetts Medical School, Beth Israel Deaconess Medical Center and the Aging Brain Center at Hebrew SeniorLife reported. The authors suggested that clinicians should intervene before surgery to prevent delirium onset.
Jane S. Saczynski, PhD, one of the first authors of the study who is an assistant professor of medicine at University of Massachusetts Medical School, told Neurology Today that “the prolonged period of impairment could impede functional recovery of patients since physical function and cognitive function are so intertwined.
“Patients who develop delirium after surgery may need to be more closely monitored after surgery in the weeks and months after discharge and many need to have rehabilitation services more tailored or extended in order to maximize their recovery,” she said. [See “Interventional Strategies for Preventing Delirium Before Surgery” for more suggestions.]
The analysis included patients aged 60 or older who were planning to undergo coronary-artery bypass grafting or valve replacement. The investigators assessed cognition through the Mini-Mental State Examination (MMSE). To diagnose delirium, they used the Confusion Assessment Method, a diagnostic algorithm for delirium using four features: acute change with a fluctuating course, inattention, disorganized thinking, and altered level of consciousness. Assessments took place preoperatively; daily during hospitalization starting at day 2; and also at 1, 6, and 12 months post-surgery.
Among their findings, the investigators reported that patients with delirium had lower preoperative mean MMSE scores than those who didn't develop delirium (25.8 vs. 26.9, p<0.001). After adjusting for baseline differences, the between-group difference in mean MMSE scores was significant 30 days after surgery (p<0.001) but not at 6 or 12 months (p = 0.056 for both). A higher percentage of patients with delirium than those without delirium had not returned to their preoperative baseline level at 6 months (40 percent vs. 24 percent, p = 0.01), but the difference was not significant at 12 months (31% vs. 20%, P = 0.055).
“Future studies should be also looking at these same cognitive trajectories in other patients — not only those undergoing cardiac surgery,” Dr. Saczynski said. “Is delirium associated with a long-term change in cognitive function for all patients [undergoing hospital procedures]? It's very well documented that delirium is associated with short-term changes in cognitive function but the findings for long-term associations are much less clear.”
Commenting on the study, Cathy Sila, MD, professor of neurology and director of the stroke center at the University Hospitals Case Medical Center, noted that the investigators used several standardized measures for both delirium and cognitive functions. “All these tests have pretty high sensitivity and specificity for the diagnosis of delirium, so they were very precise when they diagnosed post-operative delirium in 46 percent of patients,” she said.
This is an important and well--performed study that really opens up more opportunities for patient-centered care, Dr. Sila told Neurology Today. She noted, however, that cognitive decline in some of the patients might be linked with post-procedural cerebral infarction.
Dr. Sila believes that patients with delirium in the hospital setting “are experiencing an unmasking of an underlying cognitive impairment,” although the study did not include extensive or serial neurocognitive testing in the pre-operative period. These patients, she said, “should be followed carefully and reassessed at intervals; even though they may recover, we should consider those individuals at much higher risk for developing symptomatic cognitive impairment or dementia in the future.
“Although the investigators say that they excluded  patients who suffered a post-operative stroke from their analysis, they did not require diffusion-weighted MRI imaging to exclude subclinical strokes,” she said. There have been a number of studies in cardiac patients where prospective imaging with diffusion-weighted imaging (DWI) have identified new DWI lesions in a high percentage of the patients, she added.
Ola Selnes, PhD, professor of neurology and psychiatry at Johns Hopkins University School of Medicine, noted another limitation. “Testing the patients two days after major surgery is a risky enterprise because you simply don't know exactly why patients may be doing poorly right after major surgery,” said Dr. Selnes, who has studied postoperative cognitive outcomes in patients undergoing coronary artery bypass graft.
“It could be lingering effects of anesthesia, post-operative pain, medication side effects, sleep disturbances — so there are a host of confounding issues when you choose to evaluate a patient as soon as two days after surgery. Most investigators would prefer to wait at least seven days before attempting to do a cognitive assessment like this.”
Dr. Selnes noted that older age is still the most important risk for postoperative delirium, and it may be worth discussing the risk-benefit-ratio of a major cardiac surgical procedure in patients. “Many of the patients in this study were over 80 years old, which may explain the high rate of delirium reported in this study,” he said. Also, the baseline MMSE scores were very low in this study, he pointed out, which also likely accounts for the high percentage of patients who developed delirium.
Significantly, this study has identified that delirium after cardiac surgery is very common — “so common that we (neurologists) should be routinely assessing patients for cognitive function post-operatively and providing appropriate treatments,” Dr. Sila said. For example, she recommended the use of reorientation, cognitive stimulation, and hospital procedures to encourage early mobilization, a quiet nighttime environment to promote normal sleep-wake cycles, and fall prevention. “We should also remember that when we do patient education and discharge instructions, we can't rely on educating the patient alone. We have to reinforce these instructions with family and caregivers, and be very careful to assess them for some sort of appropriate rehabilitation services at the time of discharge.”
INTERVENTIONAL STRATEGIES FOR PREVENTING DELIRIUM BEFORE SURGERY
What can clinicians do to help prevent delirium before surgery? One approach, suggested by one of the first study authors, Edward Marcantonio, MD, focuses on incorporating a broader team into the management of older patients when they are in the hospital, including geriatricians, who may be more attuned to both risk factors and symptoms of delirium.
“One of the major problems with delirium is that very often it goes undiagnosed — patients can have a longer duration of delirium because it's not recognized or treated. Including geriatricians and also neurologists into the group that's routinely caring for the patient is one preventative strategy,” said Jane S. Saczynski, PhD, a first author of the study who is an assistant professor of medicine at University of Massachusetts Medical School.
Another intervention, developed by one of the senior authors on this article, Sharon Inouye, MD, MPH, is the Hospital Elder Life Program (HELP) — used in several hospitals both nationally and internationally. Mostly, Dr. Saczynski explained, it relies on behavioral changes that are as simple as making sure that patients are allotted enough time to sleep at night (not waking them up in the middle of the night for tests and procedures that could be performed in waking hours) or making sure that they have eye glasses and hearing aids to prevent disorientation. “It is also important to try to promote orientation by having clocks in the patient's room and having the date displayed. A lot of these prevention strategies seem almost like common sense, but they are often overlooked,” she noted.
Ola Selnes, PhD, professor of neurology and psychiatry at Johns Hopkins University School of Medicine, contends that preoperative cognitive assessment with the MMSE, if there's no other test available, “can actually be a surrogate marker for pre-existing neurological disease, and might predict who is vulnerable for post-operative delirium.” Those with lower scores should be examined more carefully, and then clinicians can review things like preoperative medications, hemoglobin levels, and other issues that could make patients more prone to post-operative delirium. “It's conceivable that you could reduce the risk of post-operative delirium. But as far as I know, there's no specific treatment that you can administer prior to surgery to make a major surgical procedure ‘delirium-proof,’” he said.
Cathy Sila, MD, discusses delirium and long-term cognitive decline in cardiac surgery patients, as well as strategies for improving screening and care for this population: http://bit.ly/rCBryX.
©2012 American Academy of Neurology
• Saczynski JS, Marcantonio ER, Jones RN, et al. Cognitive trajectories after postoperative delirium. N Engl J Med
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