Cognitive Decline After CABG
Abstract & Commentary
By Michael H. Crawford, MD
Source: Djaiani G, et al. Continuous-flow cell saver reduces cognitive decline in elderly patients after coronary bypass surgery. Circulation. 2007;116:1888-1895.
Cognitive decline after surgery requiring cardio-pulmonary bypass (CPB) may be due to cellular debris picked up by the cardiotomy suction device. Cell savers, which clean and process shed blood prior to retransfusion, are used extensively during non-cardiac surgery, but have not been systematically studied in cardiac surgery. Thus, Djaiani and colleagues from Toronto, Canada, hypothesized that using a cell saver instead of the cardiotomy sucker would reduce cognitive decline after CABG. A cohort of 226 patients > age 60 years scheduled for CABG were randomized to cell saver or control with cardiotomy suction. Exclusion criteria included redo surgery, other cardiac surgery required, emergency surgery, symptomatic cerebrovascular disease, or atrial fibrillation. A preoperative transesophageal echo was done to exclude a cardiac source of emboli. Transcutaneous Doppler detected emboli were assessed during aortic clamping in a subgroup of patients. Neuropsychological testing was performed one week before surgery and 6 weeks after.
Results: Baseline data were not different in the 2 groups. Cognitive dysfunction occurred in 6% of the cell saver group and 15% of the control patients (P = .038). Cognitive improvement occurred in 19 vs 17% of patients (P = NS). There was no difference in aortic atheroma. Doppler embolic counts, which could be done in about one third of patients, was 90 in the cell saver group and 133 in the control (P = NS). Retransfusion blood volume was a median of 800 mL in the control group and 401 mL in the cell saver group. Djaiani et al concluded that processing shed blood with a cell saver before retransfusion resulted in a clinically significant reduction in cognitive dysfunction post CABG.
A cardiotomy suction device that returns blood from the pericardium and thorax to the patient's circulation is an integral part of CPB that reduces blood loss and blood transfusion requirements. However, this blood has been shown to contain high levels of lipid microparticles and cellular debris, which can cause microembolization of the brain. These microemboli are likely an important cause of cognitive decline after cardiopulmonary bypass. Previous studies have documented significant cognitive declines in 7-14% of patients undergoing cardiopulmonary bypass, about half of which are frank strokes, probably due to large emboli from cellular debris. The other half are more subtle declines detectable by neuropsychological testing and are probably due to microemboli from lipids. Cell savers, which are used extensively in other types of vascular surgery, separate red blood cells from plasma and debris by washing and differential centrifugation. In this study, their use decreased cognitive decline by 60% and eliminated stroke. Interestingly, Transcranial Doppler emboli counts were not different, suggesting that these come mainly from aortic manipulation, which would not be affected by the cell saver. Thus, the cell saver's effect on reducing cognitive decline is probably due to removing lipid microparticles and smaller cellular debris. Also, the cell saver removes inflammatory mediators in the plasma, which may decrease the inflammation reaction to microemboli.
The cell saver increases hemoglobin during the first 24 hours after surgery, but also increases INR by removing clotting factors and reducing platelets. Blood loss and transfusion requirements were the same in both groups in this study, but 2 times more fresh frozen plasma was administered to the cell saver group.
This study suggests that efforts to reduce aortic manipulation (large emboli prevented) and decrease lipid microembolization from the cardiotomy suction devices will have a major benefit on cognitive function after cardiopulmonary bypass. Whether the cell saver system will become the preferred technique for the latter will require more study, since it may have adverse effects on hemeostasis.