MO658: Effect of a Time-Dependent Dialysate Bicarbonate Concentration on Intradialytic and Postdialytic Blood Bicarbonate Kinetics

Abstract

Abstract BACKGROUND AND AIMS Use of a high dialysate bicarbonate (HCO3) concentration during haemodialysis (HD) is associated with higher patient mortality, potentially due to post-dialytic metabolic alkalosis [1]; it remains unclear how to optimize dialysate HCO3 concentration ([HCO3]) to both neutralize interdialytic acid generation and minimize post-dialytic alkalosis. We compared the effects of an intradialytic increasing or decreasing dialysate [HCO3] during HD on blood bicarbonate kinetics. METHOD Blood [HCO3] was measured in 11 chronic, thrice-weekly HD patients (5 male, 6 female) during 4-h treatments with i) constant dialysate [HCO3] of 35 mEq/L; ii) dialysate [HCO3] of 35 mEq/L for the first 2-h and 30 mEq/L for the second 2-h; and iii) dialysate [HCO3] of 30 mEq/L for the first 2-h and 35 mEq/L for the second 2-h. Treatment interventions were fixed during a given week, and arterial blood samples were obtained at the start of treatment, every hour during the treatment and 1-h after the treatment during the second and third treatments of the week; a total of 66 HD treatments were monitored. Blood acid-base composition was determined using a blood gas analyzer; [HCO3] was calculated from measured pH and partial pressure of carbon dioxide using the Henderson–Hasselbalch equation. Blood [HCO3] for each patient was averaged over the second and third treatment of the week. HCO3 transfer from dialysate to blood was calculated by numerical integration of the time-dependence of the blood bicarbonate profile assuming a constant dialyzer dialysate of 198 mL/min. Blood flow rates were 250–350 mL/min and were relatively constant for each patient; dialysate flow rates were always 500 mL/min. RESULTS Pre- and post-dialytic body weights were 71.1 ± 12.6 kg and 69.5 ± 12.1 kg [mean ± standard deviation (SD)], respectively, during the first study treatment. Mean values of blood [HCO3] are shown in the Figure; certain statistics are tabulated. Blood pH at the start of treatment was not different (P = 0.12) between Treatments A and B (7.41 versus 7.40, respectively) but was lower (P < .001) at end of treatment during Treatment B than A (7.47 versus 7.51). HCO3 transfer from the dialysate to blood during A, B and C treatments were 140 ± 58, 97 ± 47 and 120 ± 47 mEq, respectively. HCO3 transfer trended lower (P = .09) during treatment B than A. CONCLUSION HD treatments with a dialysate [HCO3] of 35 mEq/L for only the first 2-h led to a reduction in HCO3 transfer to the patient and lower post-dialytic blood [HCO3] and pH. Lowering dialysate [HCO3] after 2-h of a 4-h HD treatment can reduce post-dialytic metabolic alkalosis. Further, long-term studies with such a strategy are needed to evaluate its effect on patient outcomes.