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

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Abstract
In conscious rabbits with arterial, central venous and cisterna magna catheters, HCl, Hlactate and Hacetate were infused so as to lower and maintain plasma [HCO3-] at the same mean values in all 3 groups over 6 h. The hypothesis was that the 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 attributed to a greater stimulatory effect of Hacetate on the alveolar ventilation relative to CO2 production. 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-]. In metabolic acidosis the changes in large cavity CSF [HCO3-] may depend on changes in the PCO2. The strong anion regulated by the PCO2 changes is Cl-. In experiments with different acids, the net change in the CSF [Cl-] is the sum of this PCO2-dependent Cl- process and a non-PCO2-dependent exchange of the strong anion of the acid with CSF Cl-. The result is a PCO2 determined change in the CSF strong ion difference (and [HCO3-]).