Cognitive Outcomes after CABG

Posted by • January 19th, 2012

For patients undergoing coronary-artery bypass grafting (CABG), adverse neurologic outcomes, including stroke and cognitive decline, are major concerns. Even mild cognitive deficits before surgery may be a marker for cerebrovascular disease and increased risk.  This latest article in our Current Concepts review series comes from Dr. Ola Selnes and others at Johns Hopkins.

Patients referred for coronary revascularization procedures are older and have a greater burden of extracardiac vascular disease than those referred for such procedures in the past. Despite these trends, mortality rates for coronary-artery bypass grafting (CABG) have continued to decline. Nevertheless, adverse neurologic outcomes, including stroke and cognitive decline, remain a major concern for these older patients.

Clinical Pearls

Which clinical factors are predictors of postoperative neurologic complications, including stroke?

Older age, history of stroke, and history of hypertension and diabetes are each predictors of postoperative neurologic complications, including stroke. Other risk factors include atherosclerosis of the ascending aorta, carotid stenosis, history of peripheral vascular disease, cigarette smoking, and previous cardiac surgery. Anemia is also strongly associated with the risk of adverse perioperative and postoperative outcomes, including stroke.

Table 1. Risk Factors for Perioperative Stroke during On-Pump CABG.

What preoperative or intraoperative strategies may be helpful in minimizing postoperative cognitive, neurologic decline, or both?

Strategies to minimize the incidence of postoperative stroke and cognitive decline should focus on careful preoperative assessment of known risk factors, such as a history of preoperative anemia or preexisting cerebrovascular disease or infarctions. More widespread use of preoperative and intraoperative assessment of specific risk factors, such as ascending aortic atherosclerosis, has now made it possible to individualize the surgical approach in high-risk patients and thus potentially reduce the occurrence of perioperative and postoperative strokes. Another risk factor is the presence of preoperative mild cognitive impairment. Undiagnosed mild cognitive deficits are common in candidates for CABG even before surgery and may be a surrogate marker for underlying cerebrovascular disease. Preoperative cognitive screening may be a cost-effective way of identifying such patients.

Morning Report Questions

Q: What is thought to be the mechanism of brain infarction occurring during cardiac surgery?

A: The traditionally invoked mechanism of brain infarction occurring during cardiac surgery is that of macroembolization or microembolization. More recent data suggest, however, that hypoperfusion and the systemic inflammatory response may also be presumed sources of neurologic injury. To date, most adaptations in surgical technique have focused on reducing the embolic burden, with the assumption that this is the primary mechanism by which neurologic injury occurs. It is likely, however, that other mechanisms of injury are involved, possibly in conjunction with embolization. Persons with chronic hypertension may be exposed to relative intraoperative  hypotension to the brain if their blood pressure is maintained at a normal or slightly low level during surgery, thus placing them at risk for a watershed stroke. In many cases, however, neurologic injury is due to a combination of these factors. Some authors have proposed that the combination of hypoperfusion and microembolization increases the risk of neurologic injury owing to decreased washout of emboli. Because of the likely multifactorial mechanisms underlying stroke after CABG, preventive strategies may need to be designed not only to avoid excessive release of emboli (e.g., from clamping of a particularly diseased part of the aorta) but also to avoid relative hypotension or a systemic inflammatory response.

Q: Does the use of extracorporeal cardiopulmonary bypass negatively affect neurologic outcomes?

A: Owing partly to the assumption that adverse neurologic events were specifically related to the use of extracorporeal cardiopulmonary bypass, techniques were developed for performing CABG without the use of cardiopulmonary bypass (i.e., off-pump surgery). However, recent large, prospective, randomized studies comparing the rate of adverse neurologic outcomes after conventional on-pump surgery with the rate after off-pump surgery have not shown a significant risk reduction associated with the use of off-pump surgery. Consequently, efforts to reduce the incidence of postoperative neurologic injury have begun to focus on patient-related risk factors, such as the degree of atherosclerosis of the aorta, the carotid arteries, and the brain, rather than procedure-related variables.

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