The effects of vasoactive agents, platelet agonists and anticoagulation on thrombelastography

Background: Platelet activation is a critical step in primary hemostasis and clot formation. We tested a hypothesis that platelet stimulating effects of vasoactive agents or platelet agonists could be shown using thrombelastography (TEG®) as faster onset or increased clot strength. We further examined if TEG® could be modified to evaluate activated platelets as a reversal of anticoagulation in the presence of partial thrombin inhibition. Methods: Blood samples were obtained from 126 non-cardiac surgical patients. Effects of vasoactive agents on TEG® and aggregometry were examined using epinephrine, norepinephrine, vasopressin, desmopressin acetate, milrinone and olprinone (Experiment I). Platelet agonists (epinephrine, ADP and collagen) were separately tested on TEG® (Experiment II). Effects of platelet agonists (ADP and collagen) on TEG® under anticoagulation in the absence or presence of abciximab were studied (Experiment III). We also tested antiplatelet effects of milrinone and olprinone in the presence of anticoagulants on TEG® (Experiment IV). Results: Neither vasoactive agents nor platelet agonists affected TEG® or aggregometry results except for milrinone and olprinone on aggregometry (Experiment I, II). Platelet agonists facilitated clotting in the presence of anticoagulants (Experiment III). Abciximab-treated platelets still exhibited procoagulant effects in the presence of heparin, while not in the presence of argatroban (Experiment III). Platelet inhibition on the modified TEG® was more extensive with milrinone than olprinone, and it was dose dependent (Experiment IV). Conclusion: Modified TEG® using heparin or argatroban might delineate the procoagulant effects of platelets by adding platelet specific agonist.