An Assessment of Cardiopulmonary Bypass-Induced Changes in Platelet Function Using Whole Blood and Classical Light Transmission Aggregometry: The Results of a Pilot Study

BACKGROUND: In this study, we explored whether antiplatelet medications impair whole blood impedance aggregometry after cardiac surgery and cardiopulmonary bypass (CPB) compared with classical light transmission aggregometry (LTA). METHODS: Multiplate (R) (M) assays measuring changes in electrical resistance as aggregation units over time, and LTA assays (% aggregation) induced by collagen (COL), adenosine diphosphate (ADP), or arachidonic acid were performed Simultaneously using arterial blood samples obtained before induction of anesthesia, 15 min and 3 h after neutralization of heparin in 70 consecutive patients scheduled for elective coronary artery bypass grafting. Patients in Group A (n = 48) discontinued intake of antiplatelet drugs for at least 7 days and served as controls, patients in Group B (n = 11) received aspirin 100 mg/d and those in Group C (n = 11) aspirin 100 mg/d and clopidogrel 75 mg/d (dual antiplatelet therapy) until the day before surgery. RESULTS: In patients without antiplatelet therapy, 15 min and 3 h after protamine a significant decrease in platelet aggregation was observed with all three agonists and both aggregation methods. In patients receiving aspirin alone, LTA-COL LTA-ADP and M-ADP changed significantly over time, and ADP assays of both aggregation methods showed a significant decrease in platelet aggregation 15 min after protamine in patients receiving dual antiplatelet therapy. When calculating the areas under the receiver-operating characteristic curves for discrimination of antiplatelet agents, LTA-COL was able to discriminate between controls and patients receiving aspirin or dual antiplatelet therapy 15 min and 3 h after CPB and the M-ADP assay was able to discriminate between controls and patients receiving dual antiplatelet therapy 3 h after protamine. CONCLUSION: Whole blood and classical LTA performed with all commonly used agonists enable detection of CPB-induced changes in platelet aggregation in patients not taking antiplatelet medication, whereas in patients receiving antiplatelet therapy, ADP-induced antiplatelet assays are preferable for detecting CPB-induced impairment of platelet aggregation. (Anesth Analg 2009;108:1747-54)