Heparin monitoring in sheep by activated partial thromboplastin time

Heparin anticoagulation is utilized during and after vascular surgery in animals to reduce the risk of acute or chronic thromboembolic problems. In this study, we examined variation of activated partial thromboplastin time APTT) after the intravenous bolus IV bolus) and subcutaneous SC) heparin injection in order to monitor heparin therapy in sheep. Nine healthy sheep were assigned to 3 groups A, B, and C) according to their body weights: less than 40 kg, 40 to 80 kg, and more than 80 kg, respectively. All animals were treated with heparin 300 IU/kg body weight) through two routes, and the APTT, fibrinogen, and platelet count were measured before and every hour after treatment. This showed that the APTT was increased significantly between 1 to 4 hours after IV bolus injection and between 2 to 6 hours after SC injection P < 0.05). The APTT was returned to baseline values 6 and 10 hours after the respective treatments. The APTT in Group C was consistently higher than in Group A and B after heparin treatment by the two routes. The APTT ratio entered the subtherapeutic range 5 and 8 hours after IV bolus and SC injection, respectively. The APTT ratio was maintained in the therapeutic range for about 1 and 4 hours after IV bolus and SC injection, respectively. The highest APTT ratio in Group C after SC injection of heparin was significantly higher than that in Groups A and B P < 0.05). The mean platelet counts in Groups A, B, and C before the injection were 3197 +/- 365.6, 2886 +/- 78.2, and 1861 +/- 298.0 102/microL, respectively. The mean platelet count gradually decreased without significant variation after IV bolus and SC injection. These results produced elementary data for monitoring in sheep using APTT, and suggested that heparin should be administrated by the SC route at 4-hour intervals in order to remain in the therapeutic range, after an initial IV bolus dose.