Neuroprotection during cardiac surgery: strategies to reduce cognitive decline

Gut-Brain Axis: Possible Role of Gut Microbiota in Perioperative Neurocognitive Disorders

Aging is becoming a severe social phenomenon globally, and the improvements in health care and increased health awareness among the elderly have led to a dramatic increase in the number of surgical procedures. Because of the degenerative changes in the brain structure and function in the elderly, the incidence of perioperative neurocognitive disorders (PND) is much higher in elderly patients than in young people following anesthesia/surgery. PND is attracting more and more attention, though the exact mechanisms remain unknown. A growing body of evidence has shown that the gut microbiota is likely involved. Recent studies have indicated that the gut microbiota may affect postoperative cognitive function via the gut-brain axis. Nonetheless, understanding of the mechanistic associations between the gut microbiota and the brain during PND progression remains very limited. In this review, we begin by providing an overview of the latest progress concerning the gut-brain axis and PND, and then we summarize the influence of perioperative factors on the gut microbiota. Next, we review the literature on the relationship between gut microbiota and PND and discuss how gut microbiota affects cognitive function during the perioperative period. Finally, we explore effective early interventions for PND to provide new ideas for related clinical research.

Postoperative Cognitive Dysfunction after Coronary Artery Bypass Grafting

Postoperative cognitive dysfunction is a common complication following cardiac surgery. The incidence of cognitive dysfunction is more pronounced in patients receiving a cardiac operation than in those undergoing a non-cardiac operation. Clinical observations demonstrated that pulsatile flow was superior to nonpulsatile flow, and membrane oxygenator was superior to bubble oxygenator in terms of postoperative cognitive status. Nevertheless, cognitive assessments in patients receiving an on-pump and off-pump coronary artery bypass surgery have yielded inconsistent results. The exact mechanisms of postoperative cognitive dysfunction following coronary artery bypass grafting remain uncertain. The dual effects, neuroprotective and neurotoxic, of anesthetics should be thoroughly investigated. The diagnosis should be based on a comprehensive cognitive evaluation with neuropsychiatric tests, cerebral biomarker inspections, and electroencephalographic examination. The management strategies for cognitive dysfunction can be preventive or therapeutic. The preventive strategies of modifying surgical facilities and techniques can be effective for preventing the development of postoperative cognitive dysfunction. Investigational therapies may offer novel strategies of treatments. Anesthetic preconditioning might be helpful for the improvement of this dysfunction.

Does preoperative carotid stenosis screening reduce perioperative stroke in patients undergoing coronary artery bypass grafting?

A number of institutions routinely perform carotid artery ultrasound screening before coronary artery bypass grafting (CABG) to identify carotid artery disease requiring revascularization before or during CABG, with the expectation of reducing perioperative neurologic events. The assumptions are that carotid disease is causally related to perioperative stroke and that prophylactic carotid revascularization decreases the risk of post-CABG neurologic events. Although carotid artery stenosis is a known risk factor for perioperative stroke in patients undergoing CABG, it might be a surrogate marker for diffuse atherosclerotic disease rather than a direct etiologic factor. Moreover, the benefit of prophylactic carotid revascularization in patients with asymptomatic unilateral carotid disease is uncertain. Therefore, we have reviewed the literature for evidence that preoperative carotid artery screening, by identifying patients with significant carotid artery stenosis and altering their management, reduces perioperative neurologic events in those undergoing CABG.

Cardioprotection during cardiac surgery

Coronary heart disease (CHD) is the leading cause of morbidity and mortality worldwide. For a large number of patients with CHD, coronary artery bypass graft (CABG) surgery remains the preferred strategy for coronary revascularization. Over the last 10 years, the number of high-risk patients undergoing CABG surgery has increased significantly, resulting in worse clinical outcomes in this patient group. This appears to be related to the ageing population, increased co-morbidities (such as diabetes, obesity, hypertension, stroke), concomitant valve disease, and advances in percutaneous coronary intervention which have resulted in patients with more complex coronary artery disease undergoing surgery. These high-risk patients are more susceptible to peri-operative myocardial injury and infarction (PMI), a major cause of which is acute global ischaemia/reperfusion injury arising from inadequate myocardial protection during CABG surgery. Therefore, novel therapeutic strategies are required to protect the heart in this high-risk patient group. In this article, we review the aetiology of PMI during CABG surgery, its diagnosis and clinical significance, and the endogenous and pharmacological therapeutic strategies available for preventing it. By improving cardioprotection during CABG surgery, we may be able to reduce PMI, preserve left ventricular systolic function, and reduce morbidity and mortality in these high-risk patients with CHD.

Effect of remote ischemic preconditioning on clinical outcomes in patients undergoing coronary artery bypass graft surgery (ERICCA): rationale and study design of a multi-centre randomized double-blinded controlled clinical trial

BACKGROUND

Novel cardioprotective strategies are required to improve clinical outcomes in high risk patients undergoing coronary artery bypass graft (CABG) ± valve surgery. Remote ischemic preconditioning (RIC), in which brief episodes of non-lethal ischemia and reperfusion are applied to the arm or leg, has been demonstrated to reduce perioperative myocardial injury following CABG ± valve surgery. Whether RIC can improve clinical outcomes in this setting is unknown and is investigated in the effect of remote ischemic preconditioning on clinical outcomes (ERICCA) trial in patients undergoing CABG surgery. (ClinicalTrials.gov Identifier: NCT01247545).

METHODS

The ERICCA trial is a multicentre randomized double-blinded controlled clinical trial which will recruit 1,610 high-risk patients (Additive Euroscore ≥ 5) undergoing CABG ± valve surgery using blood cardioplegia via 27 tertiary centres over 2 years. The primary combined endpoint will be cardiovascular death, non-fatal myocardial infarction, coronary revascularization and stroke at 1 year. Secondary endpoints will include peri-operative myocardial and acute kidney injury, intensive care unit and hospital stay, inotrope score, left ventricular ejection fraction, changes of quality of life and exercise tolerance. Patients will be randomized to receive after induction of anesthesia either RIC (4 cycles of 5 min inflation to 200 mmHg and 5 min deflation of a blood pressure cuff placed on the upper arm) or sham RIC (4 cycles of simulated inflations and deflations of the blood pressure cuff).

IMPLICATIONS

The findings from the ERICCA trial have the potential to demonstrate that RIC, a simple, non-invasive and virtually cost-free intervention, can improve clinical outcomes in higher-risk patients undergoing CABG ± valve surgery.

Early results of a comprehensive operative and perfusion strategy to attenuate the incidence of adverse neurological outcomes in on-pump coronary artery bypass grafting (CABG) patients

Adverse neurological events, both focal (Type I) and non-focal (Type II), have been appreciated in postoperative on-pump coronary artery bypass grafting (CABG) patients for many years. Advanced age is a significant risk factor for adverse neurological events following CABG surgery. With full knowledge that our elderly population of patients was at high risk for these untoward neurological events, we adopted a comprehensive operative and perfusion strategy in an attempt to attenuate the incidence of these complications. Our strategy included efforts to minimise the number of emboli generated during the operation, avoid cerebral hypoperfusion, and attenuate the systemic inflammatory response. From 15 August 2002 to 31 December 2005, we performed 355 on-pump CABG operations. The incidence of Type I focal injury was 0/355 (0%), the incidence of Type II non-focal injury was 9/355 (2.5%), and postoperative mortality was 2/355 (0.6%). These results compared favorably to the results predicted by the Society of Thoracic Surgeons' (STS) model, and may suggest efficacy.

Cardiopulmonary bypass management and neurologic outcomes: an evidence-based appraisal of current practices

Neurologic complications after cardiac surgery are of growing importance for an aging surgical population. In this review, we provide a critical appraisal of the impact of current cardiopulmonary bypass (CPB) management strategies on neurologic complications. Other than the use of 20-40 microm arterial line filters and membrane oxygenators, newer modifications of the basic CPB apparatus or the use of specialized equipment or procedures (including hypothermia and "tight" glucose control) have unproven benefit on neurologic outcomes. Epiaortic ultrasound can be considered for ascending aorta manipulations to avoid atheroma, although available clinical trials assessing this maneuver are limited. Current approaches for managing flow, arterial blood pressure, and pH during CPB are supported by data from clinical investigations, but these studies included few elderly or high-risk patients and predated many other contemporary practices. Although there are promising data on the benefits of some drugs blocking excitatory amino acid signaling pathways and inflammation, there are currently no drugs that can be recommended for neuroprotection during CPB. Together, the reviewed data highlight the deficiencies of the current knowledge base that physicians are dependent on to guide patient care during CPB. Multicenter clinical trials assessing measures to reduce the frequency of neurologic complications are needed to develop evidence-based strategies to avoid increasing patient morbidity and mortality.