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Objective To evaluate hemostatic changes following experimental acute hemorrhage in dogs using traditional coagulation tests (eg, platelet count, prothrombin time [PT], and activated partial thromboplastin time [aPTT]), kaolin-activated thromboelastography (TEG), and whole blood multiple electrode impedance platelet aggregometry. Design Prospective study. Setting Research laboratory. Animals Five Beagles. Interventions Dogs were anesthetized prior to obtaining blood samples for baseline PCV, total plasma protein (TPP), arterial blood-gas, platelet count, PT, aPTT, TEG, fibrinogen, and aggregometry. Blood was obtained at 4 additional time points, following 20% blood volume loss, 40% blood volume loss, 60 minutes of sustained hypotension, and after autologous blood transfusion. In addition, heart rate and direct arterial blood pressure were measured at each time point. Measurements and Main Results Significant decreases were noted for PCV ( P = 0.048), TPP ( P < 0.0001), and arterial blood pressures ( P < 0.0001) over time. Platelet count did not change significantly ( P = 0.879), but platelet function was decreased following hemorrhage when arachidonic acid ( P = 0.004) and ADP ( P = 0.008) were used as agonists. The TEG variables R ( P = 0.030), MA ( P = 0.043), and G ( P = 0.037) were significantly, albeit mildly, changed following hemorrhage. Significant prolongations in PT ( P < 0.0001) and aPTT ( P = 0.041), and decreases in fibrinogen concentration ( P = 0.002) were also seen. Conclusion Platelet dysfunction occurred following hemorrhage in this model, despite a stable platelet count. Additionally, significant changes associated with hemorrhage were documented in aPTT, fibrinogen, and MA. Platelet function testing in dogs with naturally occurring hemorrhage warrants further investigation. [ABSTRACT FROM AUTHOR]