Interrelations Between Total Exchangeable Sodium, Potassium, Body Water, and Serum Sodium and Potassium Concentrations in Hyponatremic and Normonatremic Heart Disease

Abstract

Interrelations between total body water, total exchangeable cation (sodium + potassium), and cation (sodium + potassium) concentration of serum water were examined in 20 normonatremic and 11 hyponatremic edematous cardiac patients. The total exchangeable cation and total body water were highly significantly correlated in the normonatremic and hyponatremic groups. However, for the combined groups the correlation coefficient was lower than that found in the individual populations, and in covariance analysis the cation content in relation to total body water was significantly lower in the hyponatremic than in the normonatremic group. When it is assumed that the total exchangeable cation differs little from the total osmotically active cation, and that the cation concentrations of the extracellular and intracellular water are approximately equal, the ratio: total exchangeable cation ÷ cation concentration in serum water, that is, the cation space, should reflect the total body water. The cation space and total body water were highly significantly correlated in the normonatremic and hyponatremic groups, and the correlation coefficient remained at the same high level for the combined groups. The relationship between cation space and body water was very close to unity, and in covariance analysis no significant difference was found in cation space in relation to total body water. These results were confirmed in 10 sequential studies. It is concluded that the cation space in hyponatremic and normonatremic cardiac patients has proved to reflect the total body water very closely, and the implications of this finding are discussed.