The Volume of Distribution of Sodium Thiosulfate

The importance of total body fluid and electrolytes and their distribution in the body cell mass has been increasingly emphasized in the care of acutely and chronically ill patients. In order to determine distribution of water and electrolytes, a convenient and accurate technique for the estimation of the extracellular fluid space is essential. Moore (1) has demonstrated that the chemical dissection of the patient (to determine total body composition) is feasible by the dilution of radioactive and stable isotope tracers used in conjunction with a means for measuring the extracellular fluid. While techniques such as deuterium dilution, tritium dilution, and antipyrine dilution for the in vivo measurement of total body water can be checked for absolute accuracy against desiccation and specific gravity measurements (2), no such criterion for the accuracy of extracellular fluid measurements is available. Evaluation of extracellular fluid techniques must depend upon their reproducibility and compatibility with microanatomical studies and estimations of the volume of distribution of normal extracellular constituents. In addition to interstitial and plasma water, the extracellular compartment must be considered to include the cerebrospinal fluid, water in the gastrointestinal tract, in glandular lumina, and bone matrix water. No technique is at present available which has been proven to measure the absolute volume of the entire compartment. Indeed at certain points the exact boundaries of the "com-