Relation between Urinary Bicarbonate Concentration and Carbon Dioxide Tension in Patients with Proximal or Distal Renal Tubular Acidosis

Abstract

UEDA, H. Relation between Urinary Bicarbonate Concentration and Carbon Dioxide Tension in Patients with Proximal or Distal Renal Tubular Acidosis. Tohoku J. exp. Med., 1981, 133 (1), 21-32 The relation of urinary bicarbonate concentration (U_HCO3^-) to the difference between urinary pCO₂ and arterial blood pCO₂ (U-BpCO₂) has not yet been clearly elucidated either in normal subjects or in patients with distal renal tubular acidosis (distal RTA). Nor are there any reports dealing with the relation between U_HCO3^- and U-BpCO₂ in patients with hypokalemia or with proximal renal tubular acidosis (proximal RTA). In the present study, with the objective of analyzing the differences in the production of urinary pCO₂ in different groups of patients with hypokalemia, those with distal RTA and those with proximal RTA, we loaded these patients and control subjects with sodium bicarbonate, and studied the changes in the relations between U_HCO3^- and U-BpCO₂. The following results were obtained: (1) (a) When U_HCO3^- was higher than 130mEq/liter: Normal subjects had a positive correlation between U_HCO3^- and U-BpCO₂ (p<0.001). In the patients with hypokalemia and distal RTA, U-BpCO₂ tended to show lower levels than in the control subjects when compared on the same level of U_HCO3^-. In the patient with proximal RTA, U-BpCO₂ was higher than that in the control when compared on the same level of U_HCO3^- (p<0.001). (b) When U_HCO3^- was lower than 130mEq/liter: Normal subjects showed no correlation between U_HCO3^- and U-BpCO₂ (p>0.7). In the patients with distal RTA, U-BpCO₂ was lower than that in the control (p<0.005). (2) In the patients with hypokalemia, after the loading of potassium chloride, U-BpCO₂ tended to rise compared on the same level of U_HCO3^-. (3) In the control subjects loaded with a large dose of phosphate, the values of U-BpCO₂ compared on the same levelof U_HCO3^- were not distinctive compared with those in other control subjects, when U_HCO3^- was over 130mEq/liter. These results suggest that in the patient with proximal RTA, an increase in bicarbonate load in the distal tubule is likely to augment the formation of carbonic acid, raising the value of U-BpCO₂. The fact that in the patients with distal RTA U-BpCO₂ was lower than that in the control subjects seems to be attributed not only to the low value of U_HCO3^- due to potassium deficiency but also to the impairment of secretion of hydrogen ion in the distal tubule.