CSF and plasma ions and blood gases during organic metabolic acidosis in conscious rabbits.

In conscious rabbits with arterial, central venous, and cisterna magna catheters, we infused HCl, Hlactate, and Hacetate so as to lower and maintain plasma [HCO3-] at the same mean values in all three groups over 6 h. The hypothesis was that the cerebrospinal fluid (CSF) [HCO3-] will depend on the changes in CO2 partial pressure (PCO2) and be determined by the net increase in the CSF concentration of the strong anion of the acid. The delta CSF [HCO3-] did correlate strongly with the delta PCO2, with the largest decrease in CSF [HCO3-] and PCO2 being in the Hacetate group, a response we attribute to a greater stimulatory effect of Hacetate on the alveolar ventilation relative to CO2 production. However, the delta CSF [HCO3-] was not simply determined in all cases by the increase in the CSF concentration of the strong anion of the acid. In HCl acidosis, statistically delta CSF [HCO3-] was equal to delta CSF [Cl-]. In H lactate acidosis delta CSF [HCO3-] was equal to the sum of a small positive delta CSF [lactate] and a small positive delta CSF [Cl-]. In Hacetate acidosis, delta CSF [HCO3-] was equal to the sum of a large positive delta CSF [acetate] and a small negative delta CSF [Cl-]. We hypothesize that in metabolic acidosis the changes in large cavity CSF [HCO3-] depend on changes in the PCO2. The strong anion regulated by the PCO2 changes is Cl-.(ABSTRACT TRUNCATED AT 250 WORDS)