Figure 4
From: Bench-to-bedside review: Fundamental principles of acid-base physiology
Stewart's 'independent variables' ([SID+], [ATOT] and PCO2), along with the water dissociation constant (K'w), determine the 'dependent' variables [H+] and [HCO3-]. When [ATOT] = 0, Stewart's model simplifies to the well-known Henderson–Hasselbalch equation. [ATOT], total concentration of weak acids; PCO2, partial CO2 tension; SID+, strong ion difference.