Microsoft word - abstract - stp mezger.doc

Platelet function in relation to blood loss and need for transfusion in coronary Abstract Background One of the major problems during coronary artery bypass grafting (CABG) is excessive perioperative bleeding, in about half of the cases due to a loss of platelet function or coagulopathy. To reduce the risk for bleeding, blood products can be transfused. Transfusion is associated with an increased morbidity of mortality in CABG patients. Platelet specific tests are available for the monitoring of the platelet function, they may be used to guide a transfusion policy. The purpose of this study is to monitor the development of the platelet function during and after CABG and to find a platelet function parameter with highest positive or negative predictive value for blood loss (> 1500 mL/24h) or the need for transfusion after CABG. Methods Patients (n = 60) undergoing first elective CABG were recruited and divided over two groups based on their antiplatelet medication. The control group (group 1, n = 38) did only use aspirin and the other group (group 2, n = 22) used both aspirin and clopidogrel until the day of surgery. The platelet function was determined pre-CPB, post-CPB and 2h post-CPB using coagulation screening and platelet specific methods. Blood loss and blood product use was registered for the first 24 hours post-operative. For a small group of four CABG patients the level of expression of the GPIIb/IIIa (fibrinogen) receptor and P-selectin was determined at five time points during CABG using flow cytometry. Results No significant differences were found when comparing blood loss or blood product use between the groups, the variable response seen for both aspirin and clopidogrel might explain the lack of significant differences. Both platelet count and platelet function showed a significant decrease directly after CABG with a return to the baseline value after arrival at the ICU. This decrease of platelet function could not be explained by the expression of the GPIIb/IIIa receptor or P-selectin, as no significant changes were found (p = 0.339 and p = 0.938). When comparing the platelet specific techniques with the gold standard light transmission aggregation (LTA), weak but significant correlations were found. This might be explained by the differences between the methods (sample material, anticoagulant, measuring technique). Tertile analysis showed that a decreased platelet function pre-operative was associated with increased bleeding (LTA collagen; p = 0.011, inhibition of AA and ADP induced aggregation; p = 0.010 and p = 0.007) and blood product use (LTA collagen; p = 0.010, inhibition of AA induced aggregation; p = 0.026). High negative predictive values were found for blood loss (group 1; PFA P2Y and PFA EPI, group 2; PFA EPI and LTA COL) and transfusion requirements (group 1; PFA ADP and MEA COL, group 2; PFA EPI, MEA COL and LTA COL). ROC-analysis gave nine platelet function parameters with high positive and negative predictive values regarding transfusion requirements for patients taking clopidogrel (LTA, MEA and TEG PM). Conclusion The data from the study did not show significant difference regarding blood loss or blood product use for patients with or without clopidogrel treatment. This lack of significant differences and the variable response to antiplatelet medication suggest that not all patients have to stop using clopidogrel before surgery. The decrease of both platelet count and platelet function was a known effect due to the cardiopulmonary bypass (CPB), which causes hemodilution and activation of platelets. Expression of the GPIIb/IIIa receptor or P-selectin did not show significant changes and the results cannot explain the decrease in platelet function. The return of the platelet function at arrival on the ICU supports the policy for bleeding patients, as the bleeding is not in all cases a result of platelet dysfunction. Platelet function parameters with high positive and/or negative predictive value (LTA, MEA and TEG PM) can be used to identify patients taking clopidogrel with a high risk of (not) having blood loss or transfusion after CABG. Pre-operative platelet function data can be used to guide a transfusion policy and thereby possibly decrease the exposure blood products.

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