DOES COLLOID-INDUCED PLASMA HYPERVISCOSITY IN HEMODILUTION JEOPARDIZEPERFUSION AND OXYGENATION OF VITAL ORGANS

Background and Methods. The infusion of dextran solutions is associate d with haemodilution and, under some conditions, with a Slight increas e in plasma viscosity. To clarify the compound effects of simultaneous haemodilution and plasma viscosity increases on macro- and microhaemo dynamics, we investigated the changes in arterial perfusion (radiolabe lled microspheres, 15 mu m circle divide) and oxygenation (tissue Po-2 ) Of vital organs using an animal model of plasma hyperviscosity. In n ine splenectomized beagles plasma viscosity was increased step by step from 1.06 (baseline) to 2.14, and 2.99 mPa's by infusion of small amo unts (4% of total blood volume) of an ultra-high-molecular-weight dext ran (50% w/v, mv: 500,000). Results. Despite the significant increase in plasma viscosity, cardiac output as well as specific organ blood fl ows in heart, brain, liver, and muscle rose steadily with each step of viscosity, while the haematocrit declined from 0.31 to 0.24 and 0.20, respectively. Medians of tissue Fog in liver peaked at a viscosity of 2 mPa's and returned to baseline values at 3 mPa's, whereas in non-wo rking skeletal muscle Po-2, values were maximal at 3 mPa's. Conculsion . These results indicate that the impact of plasma viscosity on the rh eological properties of whole blood is completely offset by the concom itant reduction of haematocrit, Thus, the comparatively minor changes in plasma viscosity observed after prolonged use of clinical dextrans and other colloids in no way compromise the perfusion and oxygenation of vital organs.