The Relationship between Arterial Pco₂ and Hydrogen Ion Concentration in Chronic Metabolic Acidosis and Alkalosis

1. An analysis was made of the relationship which exists between arterial [H⁺], Pco₂ and [HCO₃⁻] in twenty-five patients with stable metabolic acidosis and alkalosis and in three normal subjects.

2. Contrary to previous reports, the relationship between Pco₂ and [H⁺] was nonlinear and could best be described in terms of a rectangular hyperbola (Pco₂ = 962/([H⁺]-12).

3. The relationship between Pco₂ and [HCO₃⁻] was curvilinear and best described by the quadratic function 23.8 (Pco₂)²−12Pco₂[HCO₃⁻] −962 [HCO₃⁻] = 0.

4. The small acute changes in [H⁺],−[HCO₃⁻] and Pco₂ produced by infusion of the weak organic acid 5,5−dimethyl 2,4−oxazolidinedione (DMO) could be predicted from the curvilinear regression.