In Vivo Bleeding Time and In Vitro Thrombelastography Measurements are Better Indicators of Dilutional Hypothermic Coagulopathy Than Prothrombin Time

Background: The coagulopathy of trauma is generally confirmed by prothrombin time (PT) greater than 16 seconds or an international normalized ratio greater than 1.5. However, the utility of these values as a screening test is unknown. We examined different coagulation tests to determine the best predictor of coagulopathic bleeding and mortality in a small animal hemorrhage model. Method Coagulopathy was induced in male New Zealand White rabbits by warfarin (W; 2 mg/kg for 2 days; n = 7), or hemodilution and hypothermia (HH; 50% blood exchange with Hextend, 34.5 0.3 Degrees C; n = 7). Normal (N) rabbits without pretreatment served as the control (n = 7). Blood samples collected after coagulopathy induction and analyzed by prothrombin time (PT), activated partial thromboplastin time (aPTT), and thromboelastography (TEG) tests. Liver bleeding time (BT) was also measured before injury. An uncontrolled hemorrhage was created by a longitudinal splenic incision and the abdomen was closed. Rabbits were resuscitated with Hextend solution (25 mL/kg) to return blood pressure to baseline and monitored for 2 hours or until death at which time blood loss was measured. Results: Warfarin-induced coagulopathy increased BT, PT, and aPTT. TEG showed increased reaction (R) and clot formation (K) times and marked decrease in clotting rate ( angle and Vmax). Hemodi- lution hypothermia coagulopathy increased only BT and aPTT, and decreased the clotting rate (angle and Vmax) and strength of the clot. After injury, blood losses were higher in coagulopathic rabbits (W = 54.6 + or - 4.2 and HH = 51.1 + or - 8.9 mL/kg) than in normal rabbits (30.6 + or - 12.4 mL/kg) and resulted in 86%, 100%, and 0% death, respectively. BT and Vmax consistently predicted coagulopathic bleeding and death in all animals. Conclusion: Although satisfactory in warfarin-induced coagulopathy, PT was not a valid screening test for dilutional and hypothermic coagulopathy. Published in the Journal of Trauma, Injury, Infection, and Critical Care, v62 p1352-1361, June 2007. Presented at the 65th Annual Meeting of the American Association for the Surgery of Trauma, held in New Orleans, LA, 28-30 September 2006.