Figure 2

Graph of independent variables (PCO₂, [SID⁺] and [A_TOT]) versus pH. Published values were used for the rate constants K_a, K'_w, K'₁, K₃, and SCO₂. Point A represents [SID⁺] = 45 mEq/l and [A_TOT] = 20 mEq/l, and point B represents [SID⁺] = 40 mEq/l and [A_TOT] = 20 mEq/l. In moving from point A to point B, ΔSID⁺ = AB = base excess. However, if [A_TOT] decreases from 20 to 10 mEq/l (point C), then AC ≠ SID⁺ ≠ base excess. [A_TOT], total concentration of weak acids; PCO₂, partial CO₂ tension; SCO₂, CO₂ solubility; SID⁺, strong ion difference. Reproduced with permission from Corey [9].