Prevention of neurocognitive dysfunction in cardiac surgical patients: Is there an optimal approach?

Worldwide, about 2 million patients undergo cardiac surgery every year. These patients are usually elderly and have associated comorbidities, putting them at higher risk of developing postoperative complications.[1] Among these, neurological sequelae are the most prevalent and are classified as type I and type II. A well-defined, focal brain insult (transient ischemic attacks and stroke) constitutes type I, while type II sequelae are poorly understood brain insults (postoperative delirium [POD] or postoperative cognitive dysfunction [POCD]).[2] First described by Bedford in 1955, POCDs are the most common neurological manifestation following cardiac surgery and are generally defined as “An impairment of cognitive functions such as executive function, attention, language, visuospatial interpretation, and motor skills.”[3] As per the definition of neurocognitive dysfunction (NCD) in the Diagnostic and Statistical Manual of Mental Disorders 5th Edition, Evered et al. suggested that “Perioperative NCDs” should encompass preexisting cognitive impairment before surgery, acute events such as POD, delayed neurocognitive recovery, and POCD. Delayed neurocognitive recovery (lasting up to 30 days postoperatively) and POCD (persisting between 30 days and 1 year postoperatively) are differentiated based on the onset and duration of cognitive impairment in the postoperative period.[4] The distinction between POD and POCD is difficult. POD is a clinical syndrome occurring on or after postoperative day 1 and is characterized by an acute attentional deficit (waxing and waning) and motor symptoms (hyper- or hypoactive) that may or may not be related to emergence delirium and may be diagnosed using the confusion assessment method. On the other hand, POCD is a research idea that indicates a variable decline in performance on a neuropsychiatric test or group of tests (before and after surgery scores) and begins days to weeks (at least 7 days) after surgery and can last up to 1 year.[5] In the current issue of “The Indian Anaesthetist’s Forum,” Panda S et al.[6] have published their observation on the impact of regional cerebral oximetry monitoring by near-infrared spectroscopy (NIRS) during off-pump coronary artery bypass grafting on postoperative NCD. They concluded that a fall by 25% of regional cerebral saturation (rScO2) from baseline or an absolute value of <50% and a reduction in MAP from baseline during the period of grafting was associated with POCD. Various risk factors have been implicated in the development of POCD and can be categorized as preoperative and intraoperative. Patients with advanced age, lower educational levels, and preexisting cognitive impairment or depression are more prone to develop POCD. Similarly, surgical approach, duration of surgery and anesthesia, arterial pressure management, glycemic control, and intraoperative hemoglobin concentration are few of the important intraoperative risk factors.[7,8] In the published literature, considerable attention has been given to the NIRS-based algorithm for maintaining cerebral perfusion and oxygenation during cardiac surgery, thereby reducing the development of POCD. However, the evidence is conflicting about its clinical benefit, with some reports showing improved outcomes.[9,10] In contrast, others failed to demonstrate any significant advantage,[8,11] leading to a class IIb recommendation with a level B of evidence for its clinical use.[12] Similarly, literature on other intraoperative strategies such as choice of the anesthetic agent (volatile vs. intravenous), adjusting the depth of anesthesia (avoidance of burst suppression), choice of anesthetic technique (regional vs. general), and targeting a higher mean arterial pressure (80–90 mmHg) have been more conflicting.[8] Avoiding certain medications (pethidine, benzodiazepine, and anticholinergic) and use of dexmedetomidine (started during surgery and continued into the intensive care unit) has been found to result in less POD. On the other hand, a few recent reports have shown that preoperative risk factors are equally or even more vital than intraoperative anesthetic management for the development of POCD.[13] Although limited supporting literature is available for preoperative optimization, it serves as an attractive concept. A multidisciplinary team-based care, including perioperative geriatric consultation, has been shown to be associated with a reduction in delirium.[14] Emerging evidence supports physical activity and inspiratory muscle training in the week before elective surgery.[15] In patients undergoing cardiac surgery, Rudolph et al. found that risk factors such as low Mini-Mental State Examination score, history of stroke, low albumin, and depression were highly predictive of POD. They suggested a validated risk model for the prediction of POD by providing a score of 1 for each risk factor. In the validation cohort, the cumulative incidence of delirium was 18%, 43%, 60%, and 87% for a score of 0, 1, 2, and ≥3, respectively.[16] Similar to other diseases with multifactorial etiology, control of modifiable cardiovascular risk factors and physical activity help in preserving brain health and slowing the progression to dementia. As patients are highly receptive in the preoperative period, they must be counseled about the adoption of strategies to promote long-term physical activity and control of cardiovascular risk factors that can have important and outsized effects on long-term cognitive outcomes. In this regard, the postoperative period is equally important, where preventive strategies can be instituted against POD. These include multicomponent nonpharmacological interventions (early mobilization and exercise, cognitive stimulation, maintaining sleep hygiene, and providing vision and hearing aids), pain management (nonopioid), and avoiding high-risk medications.[17] Similar to other public health issues, an optimal approach to the prevention of NCD should be initiated weeks before the elective surgery and continued throughout the postoperative period. Ongoing research in this field is going through more light on this aspect and will certainly improve our understanding of best practices for brain health.