Causes of Brain Injury Associated with Cardiac Interventions

Background& Objective: Brain injury after cardiac surgery is a serious concern for patients and their families. Thousands of air bubbles enter the cerebral circulation during cardiac surgery, but whether these are harmful to the brain and impact adversely on cognition remains subject of speculation. The purpose of this study was to use MRI to characterise new and pre-existing cerebral ischaemic lesions in patients undergoing cardiac surgery, and to test whether the accumulation of new lesions adversely affects cognition. This study also draws upon recent advances in intra-operative bubble sizing to investigate whether high volumes of macro-bubbles have potential to result in new MRI lesions or increased risk of cognitive decline following surgery. Methods: The burden of pre-existing versus new ischaemic lesions was quantified based on analysis of 3T MR images and compared with the results of cognitive testing. Intraoperative Doppler ultrasound recordings were used to estimate the number, volume and diameters of bubbles entering the middle cerebral artery during surgery for comparison with MRI and cognitive outcome. Results: Post-operative lesions were identified in 31% of patients. Patients with pre-existing lesions were 10 times more likely to receive new lesions after surgery. Forty six percent of patients experienced postoperative cognitive decline, which was independent of whether new lesions were present. Intra-cardiac patients received over 16 times the total volume of air, 7 times as many macro-bubbles, 5 times as many emboli following aortic cross-clamp removal, and over twice as many emboli overall than CABG patients, but there were no significant differences in MRI or cognitive outcome. Conclusions: New MRI lesions and high numbers of intra-operative macro-bubbles are common during cardiac surgery, but we found no evidence of any adverse effect on cognition.