The Effects of Mild Hypothermia on Coagulation Tests and Haemodynamic Variables in Anaesthetized Rabbits

Objective: Hypothermia has been associated with coagulation defects. The purpose of this experimental study was to investigate the effect of mild hypothermia on clinically used coagulation tests and on haemodynamic variables. Methods: Nine New Zealand rabbits were subjected to mild core hypothermia by administration of general anaesthesia and exposure to room temperature of 22 degrees C for 60 minutes. Blood samples were obtained at normothermia and mild hypothermia for measurement of prothrombin time, activated partial thromboplastin time, fibrinogen levels, platelet count and haemoglobin concentration. Hypothermic values were compared to the normothermic values. Additionally, the progressive temperature drop and haemodynamic changes (blood pressure, heart rate) were recorded. Results: Core temperature decreased significantly over time changing from 39.4 +/- 0.27 to 36.6 +/- 0.28 degrees C (p = 0.0001). Prothrombin time and activated partial thromboplastin time decreased at hypothermia, but the changes were not statistically significant (p = 0.203 and p = 0.109, respectively). Platelet count, fibrinogen levels and haemoglobin concentration decreased significantly (p = 0.0001, p = 0.03 and p = 0.027) but remained within normal limits. Mean arterial pressure and heart rate declined significantly over time (p = 0.0001 and p = 0.0001, respectively). Conclusion: The results of this study suggest that short term mild hypothermia may affect the coagulation mechanism to a clinically nonsignificant extent, while haemodynamic responses are significantly suppressed.