Total Body Exchangeable Water, Sodium and Potassium in "Hospital Normal" Infants and Children

Total body exchangeable potassium is approximately 40 mEq./kg. of body weight in infants, children and young adults alike, in contrast to exchangeable water and sodium which are high per unit of body weight at birth and decrease to adult levels during the first 2 years of life. "Cell potassium concentration" calculated from exchangeable water, sodium and potassium and serum sodium concentration changes little during the period of growth and development despite other large alterations in body composition. These measurements are suggested as a further means of investigating cellular potassium status in vivo.