Relative Importance of Dextran Molecular Size in Plasma Volume Expansion

Abstract

Completely renal-excretable and nonrenal-excretable dextran fractions were compared with "Expandex" (clinical dextran soln. containing molecules varying in wt. from approx. 25,000 to 200,000) in anesthetized bled and unbled dogs. The nonrenal-excretable fractions gave optimal plasma volume expansion in bled animals, presumably due to its almost complete retention in the plasma. Infusion of "Expandex" produced good volume expansion in bled and unbled animals, but this was not as well maintained as with the nonrenal-excretable fractions. The renal-excretable fraction was relatively ineffective in expanding plasma volume due to its rapid disappearance from the plasma and equilibration with tissue fluid as well as its excretion by the kidney. All fractions of dextran used were found in thoracic duct lymph. Lymph flow was markedly increased when the renal-excretable fraction was infused into unbled dogs and when large amounts of nonrenal-excretable fractions were used in unbled animals. Marked drops in plasma protein were seen when large doses of dextran were infused into unbled animals but not in bled dogs. These are interpreted as being due to a loss of whole plasma from the circulation as a result of raised capillary pressure or increased capillary blood flow.