• Corinna Velik-Salchner, Stephan Maier, Petra Innerhofer, Christian Kolbitsch, Werner Streif, Markus Mittermayr, Michael Praxmarer, and Dietmar Fries.
• Department of Anesthesiology and Intensive Care Medicine, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria. corinna.velik@i-med.ac.at
• Anesth. Analg. 2009 Jun 1;108(6):1747-54.

BackgroundIn 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).MethodsMultiplate (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.ResultsIn 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.ConclusionWhole 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.

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