Background and objective: Perioperative hypothermia has been found to impair the coagulation cascade and to increase blood loss and transfusion requirements. The effect of concomitant in vitro heparinization on coagulation during hypo- and hyperthermic conditions has not been well defined.
Methods: In the present study, activated partial thromboplastin time was examined in vitro at 33 degrees C, 35 degrees C, 37 degrees C, 39 degrees C and 41 degrees C in normal human plasma in response to unfractionated heparin.
Results: Hypothermia <or= 35 degrees C prolonged activated partial thromboplastin time by 10% compared with test temperatures at 37 degrees C (P < 0.05). Hyperthermia alone had no effect. Unfractionated heparin (0.1-0.4 IU mL(-1)) increased activated partial thromboplastin time in a dose-dependent manner (by 189% at 0.4 IU mL(-1), P < 0.05). Test temperatures of 33 degrees C and 41 degrees C increased heparin-induced prolongation of activated partial thromboplastin time. At a heparin concentration of 0.4 IU mL(-1), hypothermia (33 degrees C) and hyperthermia (41 degrees C) prolonged partial thromboplastin time by 12% and 22%, respectively, compared with normothermic test temperature of 37 degrees C within the heparin group (P < 0.05).
Conclusions: These observations suggest that both hypo- and hyperthermia increase the response to heparin in vitro. Further studies are needed to identify the effect of patient's body temperature on heparin activity and bleeding tendency in vivo.