Analytic calculation of physiological acid-base parameters in plasma

Area of Science:

• Biochemistry
• Physiology
• Medical Chemistry

Background:

• Accurate assessment of acid-base balance is crucial in clinical settings.
• Existing methods for evaluating acid-base status can be complex and require interpretation.
• Understanding the interplay of buffer ions and pH is fundamental to acid-base physiology.

Purpose of the Study:

• To derive analytic expressions for plasma acid-base parameters.
• To investigate the behavior of these parameters under varying buffer ion concentrations and acid-base disturbances.
• To establish relationships between total titratable base, base excess (DeltaCB), strong-ion difference (DeltaSID), and Van Slyke standard bicarbonate (DeltaVSSB).

Main Methods:

• Derivation of analytic expressions relating acid-base parameters to pH, buffer ion concentration, and equilibrium constants.
• Analysis of parameter behavior under simulated respiratory and metabolic acid-base disturbances.
• Consideration of both constant and variable noncarbonate buffer ion concentrations.

Main Results:

• Analytic expressions were successfully derived for plasma total titratable base, base excess (DeltaCB), strong-ion difference (DeltaSID), and change in Van Slyke standard bicarbonate (DeltaVSSB).
• Under constant noncarbonate buffer concentrations, DeltaSID, DeltaCB, and DeltaVSSB were found to be equal.
• These equalities were not maintained when noncarbonate buffer concentrations changed, but were restored by adjusting the reference state.

Conclusions:

• The derived analytic expressions provide a quantitative framework for understanding acid-base parameters.
• The study highlights the critical influence of buffer ion concentration dynamics on the relationships between key acid-base variables.
• Adjusting the reference state is essential for maintaining the equivalence of DeltaSID, DeltaCB, and DeltaVSSB when buffer concentrations fluctuate.