The Mechanism of Acidosis Produced by Hyperosmotic Infusions*

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Abstract
The changes in acid-base equilibrium of blood following the infusion of hyperosmotic solutions were studied in nephrectomized dogs with pCO2 held constant. The infusion of hyperosmotic NaCl or mannitol solutions consistently leads to a fall in plasma HCO3" concentration and hence in blood pH. The magnitude of the fall in plasma HCO3 - concentration when corrected for erythrocyte HCO3 - readjustment and for the effects of non HCO3 -buffers can be largely accounted for by the magnitude of the osmotically induced transfer of water from the intracellular to the extracellular space. Some transfers of bicarbonate between these 2 compartments cannot be excluded, but even under rather extreme assumptions, the effect of such transfers on HCO3 - concentration is relatively small compared to the effect of dilution. A corollary of these results is that intracellular pH should rise, since HCO3 - concentration within the cells should rise as water is withdrawn. Although no studies of intracellular pH were performed in these experiments, studies of the acid-base changes in cerebrospinal fluid, another compartment that apparently permits rapid equilibration of water and pCO2 but not of HCO3 -, show that cerebrospinal fluid pH rises as blood pH falls and that this rise is due to an increased concentration of cerebrospinal fluid HCO3-.