Pathophysiology of metabolic acidosis in patients with reduced glomerular filtration rate according to Stewart-Fencl theory
Authors:
J. Havlín 1; K. Matoušovic 1; O. Schück 1; M. Horáčková 1; J. Charvát 1; K. Kotaška 2; D. Králová 1
Authors‘ workplace:
Interní klinika 2. lékařské fakulty UK a FN Motol Praha, přednosta prof. MUDr. Milan Kvapil, CSc., MBA
1; Ústav klinické biochemie a patobiochemie 2. lékařské fakulty UK a FN Motol Praha, přednosta prof. MUDr. Richard Průša, CSc.
2
Published in:
Vnitř Lék 2009; 55(2): 97-104
Category:
Original Contributions
Overview
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.
Key words:
renal insufficiency – metabolic acidosis – Stewart theory - strong ion difference - unidentified anions - [Na+-Cl–] difference
Sources
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