Cerebral injury during cardiopulmonary bypass: Emboli impair memory

Objectives: Cognitive deficits occur in up to 80% of patients after cardiac surgery. We investigated the influence of cerebral perfusion and embolizat ion during cardiopulmonary bypass on cognitive function and recovery. Methods: Cerebrovascular reactivity was measured in 70 patients before coro nary operations in which nonpulsatile bypass was used. Throughout the opera tions, middle cerebral artery flow velocity and embolization were recorded by transcranial Doppler and regional oxygen saturation was recorded by near -infrared spectroscopy. Cognitive function was measured by a computerized b attery of tests before the operation and 1 week, 2, months, and 6 months af ter surgery. Elderly patients undergoing urologic surgery served as control s. Results: Cerebrovascular reactivity was impaired preoperatively in 49 patie nts. Median (interquartile range) regional cerebral oxygen saturation fell during bypass by 10% (6%-15%), indicating increased oxygen extraction, wher eas mean middle cerebral flow velocity increased significantly by a median of 6 cm/s (both P < .0001, Wilcoxon), suggesting increased arterial tone. M ore than 200 emboli were detected in 40 patients, mainly on aortic clamping and release, when bypass was initiated, and during defibrillation. Cogniti ve function deteriorated more in patients having cardiopulmonary bypass tha n in control patients having urologic operations but recovered in most test s by 2 months. Measures of cerebral perfusion (poor cerebrovascular reactiv ity, low arterial pressures, and flow velocity in the middle cerebral arter y) predicted poor attention at 1 week (r = 0.3, P < .01, Spearman). Emboli were associated with memory loss (r = 0.3, P < .03, Spearman). Conclusions: Cognitive deficit:, were common after cardiopulmonary bypass. Occult cerebrovascular disease was more severe than expected and predispose d to attention difficulties, whereas emboli caused memory deficits. We beli eve this to be the first report of differing cognitive effects fi om emboli and hypoperfusion.