Plasma and Red Blood Cell Water and Solute

IN 1936 Yannet, Darrow, and Cary described the effect of alterations in plasma electrolytes on the concentration of red blood cell (RBC) electrolytes.¹ Using experimental animals, extracellular electrolyte was removed or increased while little change was produced in effective body water.² The conclusions drawn from these studies have provided a model for interpretation of plasma electrolyte alterations in clinical disorders. The data obtained by Darrow and Yannet confirmed the hypothesis that most of the cells of the body are freely permeable to water and provided evidence that osmotic equilibrium is usually maintained by transfer of water across cell membranes.

Because RBCs are the only readily available source of intracellular fluid, there has been considerable interest in RBC composition.^3-9 A number of investigators have provided data which permit evaluation of the relations between plasma and RBC solute concentrations. Etteldorf and associates studied 22 infants with hypotonic and 18