Effect of acute respiratory acidosis on arterial plasma osmolality

Abstract In anesthetized and nephrectomized dogs, acute respiratory acidosis was found to raise the arterial plasma osmolality: the latter exhibited a linear dependency toward Pa CO 2 over the range of 40–150 mm Hg ( Δ Osm/ Δ P CO 2 = 0.17 mOsm/mm Hg·kg H 2 O). This indicates that a P CO 2 rise entails an overall increase of body fluid osmolality, the major part of which reflects apparently the filling of whole-body CO 2 stores. The possibility of minor osmotic redistributions of body water in connection with this phenomenon involves a disproportionately large uncertainty as to the magnitude of the transmembrane cationic exchanges generally assumed to contribute to extracellular buffering in respiratory acidosis. The finding of this new link between the acid-base balance and the water-and-electrolyte equilibrium in the organism may be of interest for the interpretation of some systemic effects of acute respiratory acidosis.