Influence of intravascular molecular weight of hydroxyethyl starch on platelets.

Complications concerning the blood coagulation have been observed repeatedly after administration of highly substituted, high molecular weight hydroxyethyl starch (HES), but it has not been examined as to how intravascular molecular weight and degree of substitution of HES influence platelet number and volume after repeated administration. Thirty patients with cerebrovascular diseases were treated for 10 days with hemodilution. 500 to 1500 ml of HES 200/0.62(n=10), HES 200/0.5(n=10) or HES 40/0.5(n=10) were infused daily. During the first days, the number of platelets was not lowered beyond the dilution effect, but at the end of the therapy the number of platelets had increased in all 3 groups beyond the initial value. Platelet volume was lowered significantly in the 3 groups. HES 200/0.62 caused the largest drop in platelet volume (-10%, p<0.01). A possible explanation could be that HES macromolecules are attached to platelets or are phagocytized by them. The larger platelets are then broken down and, to compensate the loss, more thrombocytes are released. A correlation between the molecular weight of HES and the breakdown rate of the platelets can be suspected, because HES 200/0.62 has the highest intravascular mean molecular weight(121 kD) and the largest effect on platelet volume.