Electrolyte concentrations in subcutaneous tissue fluid and lymph

The electrolyte concentrations of subcutaneous lymph and tissue fluid collected with the wick technique were compared with those of blood serum. The Na+ and K+ concentrations were found to be higher in tissue fluid and lymph than in serum, Cl- concentration was lower in lymph, but in tissue fluid it was about equal to the concentration in blood serum. These relationships do not correspond to the Gibbs-Donnan equilibrium. On the basis of electrolyte concentrations and the equilibration of intravenously injected 131I albumin it is concluded that the analysis of regional lymph gives reliable information about the steady state concentration of electrolytes and small molecules in the interstitial fluid. Acute changes, especially those of macromolecule concentration in tissue fluid can be more readily followed by the analysis of the fluid obtained by the wick technique.