Molecular distribution of hetastarch in plasma and lung lymph of unanesthetized sheep.

We used high performance size exclusion chromatography (HPSEC) to measure concentrations and molecular masses of hetastarch (Het) in plasma and lung lymph of unanesthetized sheep. Our goal was to assess the osmotic effectiveness of Het in the pulmonary circulation as judged by its exclusion from lung lymph. Sheep (n = 5) received 35 ml/kg of Het (6%) over 90 min. At the end of the infusion, Het concentrations in plasma reached a peak value of 2.9 +/- 0.1% (mean +/- SD). Lymph concentrations reached a peak value of 1.3 +/- 0.3% at 4.5 h. Het molecular masses in plasma averaged 650 +/- 36 kD at 90 min, but ranged from 31 to 2,942 +/- 187 kD. Masses in lung lymph averaged 373 +/- 71 kD, and ranged from 19 +/- 2 to 1,693 +/- 514 kD (p < or = 0.05 vs. plasma). Het contributed 6.7 +/- 1.5 mm Hg to the plasma macromolecular osmotic pressure, and 3.7 +/- 1.8 mm Hg to the lymph osmotic pressure. Despite the fact that Het has the largest molecular mass of any of the current macromolecular plasma volume expanders, we found that it filtered readily into lymph, raising the lymph osmotic pressure. These findings suggest that the rationale for the osmotic performance of such solutions may need to be reconsidered.