#1694 The Cl-/HCO3-ratio as a predictor of decompensated metabolic acidosis in CKD stages G4 and G5

Abstract

Abstract Background and Aims Metabolic acidosis (MA) is a common disorder in patients with chronic kidney disease (CKD) and is associated with both a normal anion gap (AGMA) and a high anion gap (HAGMA). AGMA is typically detected early in the course of CKD, whereas HAGMA appears later in the course of CKD due to the accumulation of non-chloride anions such as phosphate, sulphate, and an array of organic acids. The anion gap (AG) is usually calculated as the difference between serum concentration of cations and anions using the formula AG=Na+-(Cl−+HCO3−). The most important anions in serum are chlorides (Cl−) and bicarbonates (HCO3−). The more advanced the CKD, the higher the AG. As eGFR decreases, a reciprocal decrease in HCO3− and an increase in chloride concentration is observed to correct the AG. The aim of this study is to determine whether the Cl−/HCO3− ratio can be used to predict decompensated metabolic acidosis with pH decline in CKD stages G4 and G5. Method A total of 115 patients (median age 63 ± 17 years), with CKD stage G4 or G5 were enrolled in this cross-sectional study. Demographic and comorbidity data was obtained from medical records, and the Charlson Comorbid Index (CCI) was calculated. A two-year clinical follow-up was conducted to assess the clinical status of each patient. The number of patients, the time dialysis was started, and deaths were all recorded. All patients were qualified for arteriovenous fistula creation in predialysis period. The arterial (A) and venous (V) blood samples were taken during surgery, directly after vessel dissection, and evaluated in a point of care testing analyzer (POCT). The ratio of arterial Cl− and HCO3− concentration were calculated. According to mean arterial pH (pH-A) the group was divided into Group A pH-A<7.33 and Group B pH-A≥7.33 (Table 1). Results In Group A was significantly lower pH-A, pH-V, HCO3−-A, HCO3−-V, pCO2-A, pCO2-V, and significantly higher both arterial and venous Cl− and the Cl−/HCO3− ratios compared to Group B. No such differences were observed in the case of AG. Cl−/HCO3−-A ratio negatively correlated with pH (r = −0.77, p < 0.01) (Fig. 1A). The discriminative power of Cl−/HCO3−-A ratio for predicting pH-A≤7.33 was 0.917 (95% confidence interval [CI] = 0.87–0.97; p < 0.01) which provided 87% sensitivity and 84% specificity (Fig. 1B). The best cut-off was 6.22 (mmol/l)/(mmol/l). Conclusion The Cl−/HCO3− ratio lower than 6.22 (mmol/l)/(mmol/l) may be used as predictor of decompensated metabolic acidosis.