Expressiveness of global coagulation parameters in dilutional coagulopathy

Plasma-free volume replacement in haemorrhage often results in dilutional coagulopathy. Prothrombin time index (PTI) and activated partial thromboplastin time (aPTT) are used for monitoring haemostasis but have not yet been clinically evaluated. Our aim was to investigate the effects of haemodilution on the course of global coagulation tests and clotting factors (CFs).

Blood samples from each of 10 volunteers were diluted with sodium chloride 0.9% (saline) or 6% hydroxyethyl starch 130/0.4 (HAES) by 30-80%. PTI, aPTT, CF, and the thrombelastometric parameters (ROTEM(®)) coagulation time (CT) and maximum clot firmness (MCF) were determined.

Dilution-dependent CF decreased in an almost linear manner and was not influenced by the diluent. Critically low activities for CF of ∼30% and a fibrinogen concentration <100 mg dl(-1) were measured at dilutions of between 60% and 75%. Critically low CF activities of about 30% were indicated by a PTI of 35-40%. PTI and MCF decreased continuously, demonstrating a good correlation with CF activities and fibrinogen. aPTT and CT showed a linear course up to a dilution of 65-75% corresponding to CF activities of 30-40%. Thereafter, values became pathological. PTI and aPTT were not influenced by the type of diluent, whereas the diluents had profound differences on results of thromboelastometry.

PTI and MCF are useful for monitoring dilution and intervention points. aPTT and CT reflect intervention points when showing pathological values. The type of diluents does not seem to interfere with PTI and aPTT, but HAES impairs haemostasis in ROTEM(®) more profoundly than saline.