Abstract
A comparative study of the effects of plasma substitutes on apparent blood viscosity was made at low and high shear rates. Red cells from normal donors were resuspended in their own plasma diluted with plasma substitutes or saline. The haematocrit was 40%. There were significant differences between the viscosities of the diluents studied. Hydroxyethyl starch and dextran substitutes had viscosities ranging from 1.7 to 2.5 times that of plasma whilst gelatins showed viscosities similar to plasma. At clinically relevant plasma dilutions there were very small effects of plasma substitutes on apparent blood viscosity at high shear rates. At low shear rates, however, there were larger changes in apparent blood viscosity. The two solutions which caused least change in apparent blood viscosity compared to no plasma dilution were 3.5% polygeline, a small molecular weight gelatin, and 6% diafiltered hydroxyethyl starch with a degree of substitution of 5 and comparatively narrow range of moderately sized molecules. The latter solution had the highest number average molecular weight of all the solutions studied and may prove advantageous in low flow states associated with capillary leak.
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