In vivo investigation into the effects of haemodilution with hydroxyethyl starch (200/0.5) and normal saline on coagulation

We have investigated the effects of haemodilution with either saline or hydroxyethyl starch (200/0.5) (HES) on blood coagulation in healthy volunteers in vivo. Standard haematological tests (packed cell volume (PCV), platelets, prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, antithrombin III, bleeding time and platelet aggregation), and thrombelastography (TEG) were performed before and after administration of either 0.9% saline 1000 ml or HES 1000 ml i.v. over a 30-min period. Dilution of PCV and platelet concentrations as a result of volume load were 9% in the saline group and 19% in the HES group. Reductions in fibrinogen (18.6% and 28.8%) and antithrombin III (25.5% and 37.8%) were significantly greater than could be explained by haemodilution alone in both groups. Indices of platelet aggregation were significantly enhanced by saline haemodilution, but not by HES, which inhibited epinephrine-induced aggregation and prolonged bleeding time. TEG in the saline group showed significantly shortened r and k times (24% and 26%, respectively), and increased α angle (24%) and maximum amplitude (MA, 6%). HES haemodilution decreased MA (11%) but did not affect other TEG variables. We conclude that haemodilution of normal blood exerted a procoagulant effect, possibly by enhancement of thrombin formation. Circulating concentrations of antithrombin III were depleted more than could be explained by haemodilution alone, leading to a hypercoagulable state. This effect was offset by an antiplatelet action of HES, which was not seen with saline. The mechanism is unknown.