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The amount needed to change the concentration of a solute requires the knowledge of its volume of distribution in the solution. Electrolytes that do not participate in active metabolic reactions have a fixed volume of distribution that corresponds to the volume of water in which they solubilize. Bicarbonate infusion is used to correct hyperchloremic metabolic acidosis. Its volume of distribution (bicarbonate space) changes with its participation in the blood buffer systems. In other words, it is not a fixed physical volume, like that of other solutes. In this paper, we shall review experimental studies that supported evidence for this knowledge and analyze the basic hypothesis to explain the phenomena. Since we have not found clinical studies in children, we shall report our experience in a group of patients with metabolic acidosis treated with bicarbonate infusion in whom apparent bicarbonate space was measured and compared with data in adults from the literature. Guidelines for amount of bicarbonate needed to increase its concentration according to baseline bicarbonate concentration will be suggested.

A systemic biokinetic model is presented for radiocarbon taken into the body as carbon dioxide or bicarbonate. Parameter values describing retention and excretion of carbon during the first few weeks after administration are based on studies of the fate of radiocarbon in human subjects after injection of labelled bicarbonate or inhalation of carbon dioxide. Data on laboratory animals administered labelled bicarbonate, carbonate or carbon dioxide provide information on the tissue distribution and long-term retention of carbon. Model predictions of the time-dependent distribution and retention of carbon differ considerably from those of models recommended by the International Commission on Radiological Protection.