Mild and moderate hypothermia increases platelet aggregation induced by various agonists: a whole blood in vitro study.

The mechanisms causing temperature-dependent bleeding, especially in hypothermic patients, warrant clarification. Therefore the aim of this study was to investigate platelet aggregation at the clinically important temperature range of 30-34 degrees C. After obtaining informed consent citrated whole blood was drawn from 12 healthy adult male volunteers, who had not taken any medication in the previous 14 days. After venipuncture blood samples were incubated at 37 degrees C until platelet testing. Platelet aggregation was performed in whole blood using the impedance aggregometer Multiplate at five different test temperatures between 30 degrees C and 34 degrees C. Aggregation responses at 37 degrees C served as controls. At temperatures of mild and moderate hypothermia (30-34 degrees C), overall platelet aggregation was increased compared to 37 degrees C. Increases were recorded in response to collagen, thrombin receptor activating peptide and ristocetin between 31 degrees C and 34 degrees C and in response to adenosine diphosphate between 30 degrees C and 34 degrees C. Overall platelet aggregation is increased at mild and moderate hypothermia down to 30 degrees C. These results indicate that bleeding complications reported in mildly hypothermic patients are not due to hypothermia-induced platelet inhibition. The pathomechanism of the overall increased platelet aggregation between 30 degrees C and 34 degrees C requires further detailed study.