ELIMINATION KINETICS OF DIFFERENT HYDROXYETHYL STARCHES AND EFFECTS ON BLOOD FLUIDITY

In a single blind randomized cross-over study 6 volunteers each receiv ed infusions of 500 ml of 6 different types of hydroxyethyl starch (HE S) solutions. Between the test periods there was a regular wash-out ph ase of 3 months. The concentration and molecular weight distribution o f the intravascular HES-molecules as well as the blood fluidity were d etermined before and up to 24 hours after the infusions. The C2/C6 sub stitution ratio and the molar substitution exert an essential influenc e on the elimination of the HES-molecules. An increase in the C2/C6 su bstitution ratio from 4.6 to 10.8 with unchanged molecular weight (MW) and molar substitution brings about an increase in the half-life of t he elimination in the beta -phase t1/2-beta from 10.4 to 19.5 hours. I n case a high C2/C6 substitution ratio is combined with a high molar s ubstitution (0.62 instead of 0.5), half-life rises up to 36.1 hours. W hereas the molecular weights of all medium-molecular HES-types (MW 200 ,000) decrease, the medium molecular weight of the low-molecular HES-t ype (MW 40,000) rises up to 102+/-9 kDalton after 24 hours. The HES-ty pe with a molar substitution of 0.5 attain a molecular weight ranging between 72+/-2 and 108+/-4 kDalton after 24 hours. High-substituted HE S (molar substitution of 0.62) in combination with a high substitution ratio showed a MW of 136+/-8 kDalton and, as such, considerably bigge r degradation products. After the infusion of all HES solutions there is a decrease in haematocrit levels which is most strongly marked with high-substituted HES in combination with a high C2/C6 substitution ra tio. Only the solutions with a high C2/C6 substitution ratio produce a n increase in plasma viscosity.