Mental Decline and Cardiac Surgery—Should We Go There?*

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Our population is aging, and with age comes inevitable mental decline (1). In addition, aging patients are more prone to postoperative complications and cognitive function is a predictor of adverse outcomes in this population (2, 3). The demographics of cardiac surgery are changing as a reflection of the aging population and recent innovations, for example, transcutaneous aortic valve replacement (4, 5). Delirium is very common after cardiac surgery and is associated with accelerated cognitive decline (6). However, to what degree preoperative cognitive decline influences subsequent development of delirium following cardiac surgery is not known and, if developed, are there additional clinical consequences? In this issue of Critical Care Medicine, Lingehall et al (7) attempt to answer this question.
In a prospective observational cohort study, initiated in 2009, 114 patients 70 years old and older completed initial assessments and were followed for 5 years post cardiac surgery. Patients with documented dementia preoperatively were excluded although those with mild cognitive decline (n = 9; Mini-Mental State Examination (MMSE) score < 24) were included. Cognitive impairment was assessed with the MMSE, and presence of delirium, depression, and dementia was assessed with the Organic Brain Syndrome scale. Physical function was assessed using the Katz Staircase of Independence in Activities of Daily Living scale and depressive symptoms were assessed using the 15-item Geriatric Depression Scale. Structured assessments were performed preoperatively, 1 and 4 days post tracheal extubation and 1, 3, and 5 years after surgery. Postoperative delirium was retrospectively diagnosed, by a physician and a nurse with specialization in geriatrics, based on the structured assessments after study completion and Statistical Manual of Mental Disorders, 4th Edition (DSMIV), Text Revision, criteria. Mean MMSE score at baseline was 27.0 ± 2.8 (maximum possible 30), 12.3% had a diagnosis of depression, 16.7% had diabetes, and 14.9% had a history of cerebrovascular disease, and the majority of surgeries were coronary artery bypass grafts (58.8%). Delirium developed in 64 patients (56.1%) postoperatively; of these 64 patients, 26 (41%) went on to develop dementia. Dementia developed in 30 patients (26%) within 5 years of cardiac surgery; of these 30, eight (27%) had a preoperative MMSE of less than 24. In a combined logistic regression analysis, the odds of dementia were seven-fold higher if one developed postoperative delirium compared to those who did not develop postoperative delirium (odds ratio, 7.57 [95% CI, 2.15–26.65]; p = 0.0016). Patients with dementia had significantly lower MMSE scores before and throughout the study period and the decline over time in MMSE was greater in those who developed dementia in this cohort than in those without. The authors concluded that older patients with mild preoperative cognitive impairment and those who develop postoperative delirium are at risk of developing dementia in the 5 years following surgery. They have also suggested preoperative screening in older patients undergoing cardiac surgery and follow-up of patients who develop postoperative delirium to enable early detection and management of dementia.
Strengths of the study include its prospective nature, duration of follow-up (5 yr), limited number of assessors making observations over the 5-year follow-up period, and rigorous use of validated assessment tools for their outcome measurements. We calculate the risk of dementia if you experienced delirium as 26 of 64 equals to 40.6% or 41% and the risk of dementia if you did not experience delirium as four of 50 equals to 8%.

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