Acid-base regulation in hemodialyzed renal failure patients: effect of serum proteins and bicarbonate buffering.

Interpretation of acid-base balance in human physiology relies on the accuracy of the Henderson-Hasselbalch equation governing pH, HCO3- concentration, and dissolved CO2 in blood. The influence of strong ions and plasma proteins is not generally assigned any quantitative importance. We have taken advantage of the electrolyte and acid-base abnormalities of patients with end stage renal failure to explore the interrelationship among these factors as they pertain to pH maintenance. We find a complex association between pH and plasma protein fractions. pH failed to correlate with the strong ion difference, net cationic equivalency of plasma proteins, pCO2, or serum phosphate considered singly or together. The pK1' for the dialysis population differed significantly from 6.10. The largest calculated value was 6.285. This difference was independent of the dialysate buffer anion composition. The loss of CO2 from blood during sample preparation in the clinical laboratory may fully account for the increase in calculated pK1' and may explain why measured venous rather than arterial total CO2 more closely matches the arterial blood gas calculated HCO3-.