This study explores the influence of the type of plasma expander used to support extreme hemodilution on the critical hematocrit (blood hemoglobin concentration where total body oxygen consumption becomes dependent on oxygen supply) by comparing starch based colloids, gelatin and Ringer’s lactate. The results show that 6% HES 130/0.4 allows the lowest critical hematocrit by comparison to 6% HES 450/0.7, 3.5% gelatin and Ringer’s lactate. This was somewhat expected in view of the many studies published in the literature. However, the experimental evaluation of all 4 solutions using a single model, species and protocol is unique and provides reliable comparisons and insights. Of interest is that low-viscosity HES 130 yields a better outcome than the higher-viscosity HES 450, contrary to previous reports. HES 130 also shows a significantly lowered peripheral vascular resistance. Findings suggest an important interplay between level of hemodilution, heart performance, vascular reactivity and plasma expanding biophysical properties that should be explored to obtain a more complete mechanistic understanding of plasma expansion by associating physiological data with the viscosity and oncotic properties of the circulating blood.

– Marcos Intaglietta