[Organ blood supply and oxygenation during limited isovolemic hemodilution with 6% HES 200/0.62 and 6% Dextran 70].

Oxygen delivery (systemic oxygen transport) is directly dependent upon cardiac output and oxygen content of the blood. The rheology of blood, however, represents a co-determinant of oxygen delivery. It has recently been argued that the increase in plasma viscosity occurring under hemodilution with dextran could be detrimental to blood flow and, hence, tissue oxygenation. METHODS. Twelve splenectomized beagles (12.5 +/- 1.7 kg) were anesthetized and randomly assigned to hemodilution to 20 vol% hematocrit (hct) with 6% hydroxyethyl starch (HES 200/0.62) or 6% dextran-70 (DX-70). The effects of hemodilution (HD) upon macrohemodynamics, plasma and blood volumes (131I dog albumin distribution), organ blood flow (radioactive-labelled microspheres, phi 15 microns), and local tissue oxygenation (pO2 multiwire surface electrode) were evaluated with special reference to any actual plasma viscosity. RESULTS. Moderate HD with either solution resulted in equivalent changes in macrohemodynamics and plasma and blood volumes. Tissue oxygen extraction increased (p less than 0.05) due to a small rise (maximally 28%) in cardiac output. HD with either solution resulted in an increase in plasma viscosity that was more pronounced in the DX-70 group (1.45 +/- 0.07 mPa.s) as compared to HES-diluted animals (1.16 +/- 0.04 mPa.s). Blood flow increased (p less than 0.01) in all organs after HD independently of the diluent. Both higher pO2 values on the surface of liver and skeletal muscle (p less than 0.01) as well as a shift of the pO2 histograms to the right indicated a more homogeneous tissue perfusion during HD. CONCLUSIONS. In normotensive animals without peripheral arterial occlusive disease undergoing moderate hemodilution, organ blood flow was independent of plasma viscosity. Systemic oxygen transport was not affected by plasma viscosity changes, but is primarily determined by systemic hct. Local surface tissue oxygenation on skeletal muscle and liver was not impaired, but rather improved during hemodilution despite raised plasma viscosity. Of the rheological factors influencing oxygen delivery, hct thus plays the predominant role while plasma viscosity is of minor importance.