Vnitr Lek 2009, 55(2):97-104

Pathophysiology of metabolic acidosis in patients with reduced glomerular filtration rate according to Stewart-Fencl theory

J. Havlín^1,*, K. Matoušovic¹, O. Schück¹, M. Horáčková¹, J. Charvát¹, K. Kotaška², D. Králová¹

¹ Interní klinika 2. lékařské fakulty UK a FN Motol Praha, přednosta prof. MUDr. Milan Kvapil, CSc., MBA

² Ústav klinické biochemie a patobiochemie 2. lékařské fakulty UK a FN Motol Praha, přednosta prof. MUDr. Richard Průša, CSc.

Aim:
Metabolic acidosis is a regular sign of renal insufficiency. Conventional assessment of acid-base balance using Henderson-Hasselbalch equation does not make identification of the cause of metabolic disorders possible as the serum HCO₃^- concentration might only reflect changes to the overall plasma ion spectrum. Therefore, we used the Stewart-Fencl approach that is based on a more detailed physical and chemical analysis and that showed that changes to serum HCO₃^- concentration are closely related to parameters not usually monitored in connection to acid-base balance.


Patient group and methodology:
We performed a single measurement of arterial or capillary blood pH and pCO₂ in 69 non-dialysed patients with glomerular filtration rate ranging from 0.04 to 0.88 ml/s/1.73 m² according to MDRD, standard calculation of serum HCO₃^- concentration using Henderson-Hasselbalch equation was carried out, and serum albumin and ion concentrations (Na⁺, K⁺, Cl, Pi) plus creatinine and urea concentrations were determined from venous blood.

Results:
Metabolic acidosis was present in 47 patients ([S-HCO₃^-] < 22 mmol/l) with the mean [S-HCO₃^-] value of 19.6 mmol/l for the entire group. We proved a statistically significant correlation between [S-HCO₃^-] and [SID] (p < 0.001), and between [S-HCO₃^-] and the individual [SID] determining factors: [Na⁺-Cl^-], [UA^-], [Pi^-], [K⁺] (p < 0.01).

Conclusion:
Reduction in [S-HCO₃^-] in non-dialysed patients with reduced glomerular filtration is predominantly associated with a decrease in [Na⁺-Cl^-] difference, the quantitative contribution of which to metabolic acidosis is more significant than the strong acids retention. In addition to [S-Cl^-] increase, [S-Na⁺] reduction too has a major role in reducing the [Na⁺-Cl^-] difference.

Keywords: renal insufficiency; metabolic acidosis; Stewart theory; strong ion difference; unidentified anions; [Na⁺-Cl^-] difference

Received: April 29, 2008; Accepted: November 20, 2008; Published: February 1, 2009  Show citation