The effect of CABG on neurocognitive functioning

Post-operative cognitive decline occurs in 20-70% of the coronary artery bypass surgery patients during the first week after surgery. After 6 weeks the incidence declines to 10-40% and remains at this level thereafter. Although the neuropsychological consequences are subclinical, they can interfere with daily life. In this paper, we discuss the impact of surgical factors, with a focus on the use of the heart-lung machine and its intra-operative embolic load. The pre-morbid cardiac condition of the patient as another underlying mechanism for cognitive decline is addressed. We also describe the methodological pitfalls in arriving at an adequate estimation of the prevalence of cognitive decline. Among these are the definition of cognitive decline, testing intervals, the-choice of cognitive domains and the appropriate use of control groups. We also pay attention to the relation between cognition, depression and anxiety. Finally, the ecological validity of this study domain is discussed. It is concluded that (1) the literature remains undecided on the role of intra-operative emboli and cognitive decline after surgery. Researchers should focus on the composition, size and location instead of the absolute number of intra-operative emboli; (2) growing awareness of neurocognitive decline in chronic vascular disease patients must challenge both clinicians and investigators. The preoperative cognitive status can increase the risk for post-operative cognitive decline; (3) researchers should include -at the least- the core battery as stated in the Statement of Consensus on assessment of neurobehavioural outcomes after cardiac surgery. They also should work towards a consensus on the definition of cognitive decline and the definition of control groups; (4) depression and anxiety as confounders for postoperative cognitive decline might lead to an overestimation of cognitive decline at least for the majority of neuropsychological domains; (5) much more attention should go to the ecological validity of this research.