Protecting the brain during cardiac surgery

grantor: University of TorontoNeurologic injury during cardiac surgery can range from neuropsychological impairment (NPI) to stroke. We performed a variety of clinical studies in cardiac surgery patients in order to define the etiologies of neurologic injury and to investigate methods of minimizing these clinically important problems. We reviewed prospectively gathered data on 12,448 consecutive patients undergoing cardiac surgery at one institution. The risk factors for stroke, as defined by logistic regression analysis, suggested that macroemboli was the predominant etiology. We also performed intraoperative transcranial Doppler ultrasonography in patients undergoing coronary bypass surgery. We determined that cerebral emboli were more likely to occur after perfusionist events, i.e. the introduction of air into the cardiopulmonary bypass circuit, than during surgical events or baseline (6.9 ± 1.1 emboli per minute versus 1.5 ± 0.4 and 0.4 ± 0.1 respectively, p < 0.001). Neuropsychological testing revealed that increased perfusionist events, and therefore increased gaseous microemboli, were associated with significantly worse postoperative cognitive function. We described several simple intraoperative techniques that can be used to minimize the number of gaseous cerebral emboli. We also performed a randomized clinical trial comparing cerebral embolic rates during aortic arch cannulation versus ascending aorta cannulation. Aortic arch cannulation resulted in a significant reduction in the number of cerebral emboli per minute (2.0 ± 0.3 versus 4.2 ± 0.9 per minute respectively, p = 0.03). We also performed a double-blinded, randomized, placebo-controlled clinical trial to assess the effects of insulin on postoperative NPI. Our interim analysis revealed that the prevalence of NPI was 31% in insulin patients (95% C.I. 16-47%) versus 49% in control patients (95% C.I. 16-47%, p = 0.14). The trial is ongoing and more patients will be required to determine the effects of insulin on NPI. We concluded from our studies that stroke during cardiac surgery is predominantly caused by cerebral macroemboli and neuropsychological impairment is predominantly caused by cerebral microemboli. Cerebral microemboli can be minimized by several intraoperative techniques, including aortic arch cannulation. Further studies are required to determine the role of pharmacologic neuroprotection, including insulin, during cardiac surgery.Ph.D