Daily variability of acid-base status and determinants of serum bicarbonate in hemodialysis patients

Aim: We aimed to evaluate daily variability of bicarbonate in hemodialysis (HD) patients and identify the factors which affect that issue. Materials and methods: Blood samples of 41 patients for bicarbonate (total carbon dioxide (CO2)) and blood gas analysis (pH, bicarbonate (HCO3-)) were obtained, pre-dialysis and post-dialysis, on the first, second, and third session of the week. Those with pre-dialysis HCO3- < 22 mmol/L in all sessions were classified as acidotic. Demographic and laboratory data of acidotic and non-acidotic groups were compared, and the factors related to HCO3- level were identified. Results: pH, tCO(2), HCO3- of the first HD session were significantly lower than those of short inter-dialytic intervals (p < 0.001, respectively). Using Blant Altman analysis, pre- and post-dialysis tCO(2) did not show good agreement with HCO3-. Acidotic patients had higher levels of serum albumin and phosphorus (p < 0.01 and p = 0.02, respectively) and were more likely to use sevelamer (p = 0.04). Also, the value of HCO3- was inversely correlated with dialysis vintage (r = -0.432, p = 0.005) and serum albumin (r = -0.427, p = 0.005). Conclusion: Since tCO(2) did not show good agreement with HCO3-, relying solely on the pre-dialysis tCO(2) values to define metabolic acidosis may increase misclassification rate. More work is needed for optimal assessment of acid base status. Also, understanding the determinants of HCO3- may guide physicians for individualized HCO3- prescription.