The neuropsychological sequelae of on- and off-pump coronary artery bypass graft surgery

[Truncated abstract] Post-operative neuropsychological decline is considered one of the major morbidity outcomes following Coronary Artery Bypass Graft (CABG) surgery. Traditional CABG uses the cardiopulmonary bypass machine to ensure a still operative field (on-pump technique), but introduces microemboli and decreases perfusion in the brain. These can potentially affect neurological integrity and compromise cognitive functioning. Alternatively, performing CABG on the beating heart (off-pump method) allows normal circulation to continue, which reduces cerebral emboli and hypoperfusion, and therefore the risk of neurological damage. On this basis, it is argued that off-pump CABG should be less detrimental to neuropsychological functioning than on-pump CABG. To date, research findings have been inconsistent, largely due to substantial disagreement about what constitutes meaningful post-CABG neuropsychological impairment. Consequently, the relationship between on-pump CABG and cognitive dysfunction remains controversial. Additionally, studies have not clearly established the candidate cognitive functions most at risk during CABG surgery, or whether the effects are transient or persisting. Methodological shortfalls, including differences in assessment times, use of control samples, and failure to account for practice effects, measurement error and regression to the mean, as well as varied and often arbitrary criteria used to define impairment, are likely to blame for the lack of clarity within the literature. Using a longitudinal study, this thesis aims to determine whether 1) pre-existing neuropsychological impairments occur in candidates for CABG surgery, 2) CABG surgery is associated with neurocognitive impairment, 3) neuropsychological function is differentially affected following on- versus off-pump CABG and, therefore, whether the CPB is responsible for neurologic injury that manifests as neuropsychological impairment.