Variation of carbonic acid pK'1g in blood and urine during NaHCO3 infusion and NH4Cl loading: a study of two renal acidotic patients.

In the Henderson-Hasselbalchequation,pH = pK + Iog(HCO/S#{149}pc02), the millirnolar partition coefficient, per mmHg pressure (S), and pK1 are considered to be constants.Combining these two constants gives pH = pK19 + log(HCO/po2). In this paper, we report the results of a study designed to test the constancy of pK19. This was done by varying the blood and urine pH in two patients by administration of NaHCO3 and NH4CI. The Pco2 pH, and total CO2 were determined independently, and the values obtained were substituted in the equation, solving for pK19. The pK19 was variable in the blood and urine of both patients. In a 16-month-old child, suffering from a transient type of renal acidosis, a linear relationship between pH and pK19 was noted. In blood, the relationship was pK19 = 10.25 0.352 pH, and for urine, pKig = 9.46 0.248 pH. When this patient was restudied six months later, the results were confirmed. Similar observations were made in a 10-year-old patient suffering from distal tubular acidosis syndrome. A linear relationship between pK19 and pH of both blood and urine was observed in this case also, but the equations were somewhat different. For blood, pK19 = 8.55 0.129 pH, and for urine, PKig = 7.78 0.028 pH. The correlation coefficient with the line of best fit in these studies ranged from 0.81 to 0.95, indicating that these observations are statistically significant.