Exhausted Capacity of Bicarbonate Buffer in Renal Failure Diagnosed Using Point of Care Analyzer

Metabolic acidosis in patients with chronic kidney disease (CKD) is a common complication. A bicarbonate concentration in venous blood (V-HCO₃^-) is a key index for diagnosis and treatment initiation. The aim of our study is to evaluate usability of acid-base balance parameters of in blood taken simultaneously from peripheral artery and the vein.

A total of 49 patients (median age 66 years [interquartile range IQR 45-75]), with CKD stage G4 or G5 were enrolled in this cross-sectional study. All patients were qualified for arteriovenous fistula creation in pre-dialysis period. The samples were taken during surgery, directly after dissection, and evaluated in a point of care testing analyzer. The arteriovenous difference in bicarbonate levels (Δ-HCO₃^-) was calculated. According to glomerular filtration rate (eGFR) the group was divided into Group A eGFR ≥ 10 mL/min/1.73 m²) and Group B eGFR < 10 mL/min/1.73 m²).

In Group A Δ-HCO₃^- was significantly higher compared to Group B. No such differences were observed in the case of V-HCO₃^-. Δ-HCO₃^- positively correlated with eGFR. The discriminative power of Δ-HCO₃^- for predicting eGFR < 10 mL/min/1.73 m² was 0.72 (95% confidence interval [CI] = 0.551-0.88; p = 0.01) which provided 67% sensitivity and 75% specificity. The best cut-off was 0.5 mmol/L.

The Δ-HCO₃^- lower than 0.5 mmol/L may be used as predictor of exhaust buffer capacity. The value of this tool should be tested in larger population.