Muscle biopsy measurement of body water and intracellular electrolytes in children.

Body water and electrolytes have been measured in normal infants and children using a muscle biopsy technique. Extracellular water, sodium, and chloride contents per kilogram dry weight are high in infancy but fall to adult values by 18 months to 2 years. Intracellular water and potassium contents are initially high, but approximate to adult levels around 6 months of age. Large variations in water and electrolyte contents have been found in apparently normal children. There is good correlation between extracellular water and sodium content, and between intracellular water and potassium content. Therefore intracellular electrolyte concentrations are similar for children of all ages. This technique is presented as a useful method of obtaining information about fluid and electrolyte balance in children.