A systematic evaluation of the effect of temperature on coagulation enzyme activity and platelet function

Background. Hypothermia is associated with an increased risk of bleeding and is a significant contributing factor to the morbidity and mortality of trauma and complicated surgical procedures. A core temperature of 33degreesC is associated with a significantly increased risk of death after trauma compared with 37degreesC. Hypothermia-associated bleeding has been hypothesized to result from dysregulation of enzymatic function, reduced platelet activity, and/or altered fibrinolysis. Methods: We systematically evaluated the effects of temperature on isolated pro- and anticoagulant enzyme processes and platelet activation and adhesion. We also evaluated the effects of temperature on complete coagulation systems (activated partial thromboplastin time and an in vitro, cell-based model of coagulation). Results: Enzyme activities were only slightly reduced at 33degreesC versus 37degreesC, and this reduction was not statistically significant (p > 0.05). Platelet activation was also not significantly reduced at 33degreesC versus 37degreesC. Conversely, platelet aggregation and adhesion were significantly reduced at 33degreesC compared with 37degreesC (p < 0.05). Below 33degreesC, however, both enzyme activity and platelet function were significantly reduced. Conclusion: Our results suggest that bleeding observed at mildly reduced temperatures (33degrees-37degreesC) results primarily from a platelet adhesion defect, and not reduced enzyme activity or platelet activation. However, at temperatures below 33degrees\C, both reduced platelet function and enzyme activity likely contribute to the coagulopathy.