Pre-dialysis and post-dialysis metabolic acidosis in patients receiving hemodialysis

Objective: The aim of the study is to investigate acid-base in patients receiving hemodialysis (HD) and the effect of HD on metabolic acidosis. Methods: We designed this single-center retrospective study. We collected all data of the pre-dialysis total carbon dioxide (tCO2). We used tCO2 and anion gap (AG) to access metabolic acidosis. The differences of tCO2 and AG between pre-dialysis and post-dialysis were compared. Metabolic acidosis was considered when tCO2< 22.0mmol/l. Metabolic acidosis was defined as high AG metabolic if AG>10. Results: Totally, we included 1452 pre-dialysis electrolyte tests. The mean pre-HD tCO2 was 21.35 ± 3.19 mmol/l. The prevalence of metabolic acidosis (pre-HD tCO2<22 mmol/L) was 58.20 %. The mean of pre-HD AG was 15.06 ± 3.69mmol/l [Median and quartile:14.9(12.78,17.4)]. 828 cases complicated with high AG metabolic acidosis. We analyzed 141 pairs of pre-dialysis & post-dialysis metabolic acidosis parameters. Before dialysis, patients had the mean of tCO2 and AG 20.77 ± 3.14 mmol/L and 15.50 ± 3.35 mmol/L, respectively. Δ[HCO3-] was 3.23 ± 3.14 mmol/L. Δ[AG] was 5.78 ± 3.29 mmol/L. After HD, the mean tCO2 was 24.90 ± 2.99 mmol/L. Although post-dialysis tCO2 was significantly higher than pre-dialysis tCO2,23 (16.31%) patients still had metabolic acidosis (tCO2<22mmol/L). The average increase of post-dialysis tCO2 concentration was only 4.13 mmol/L. Conclusion: How to correct metabolic acidosis in HD patients remains a challenge.  Alkaline dialysate can increase the level of post-dialysis [HCO3-]. At that time, the increase of bicarbonate was not as high as we expected.