Strong Ion Difference and Bicarbonate Concentration

Physicochemical Mechanism

The strong ion difference (SID) is a primary determinant of bicarbonate concentration, with a direct correlation between SID and bicarbonate concentration, according to Stewart's physicochemical approach 1, 2, 3
The SID represents one independent variable that directly determines both hydrogen ion and bicarbonate ion concentrations in plasma, calculated as the charge difference between strong cations (Na+, K+, Ca2+, Mg2+) and strong anions (Cl-, lactate) 1, 2, 3

The strong ion difference calculated simply as (Na+ - Cl-) represents the primary determinant of bicarbonate concentration, because sodium and chloride are the major strong ions in plasma 1, 2, 3
An increase in plasma chloride relative to sodium decreases the plasma SID and lowers both pH and bicarbonate, while a decrease in chloride relative to sodium increases SID and raises bicarbonate 1, 2, 3