Intradialytic acid-base changes and organic anion production during high versus low bicarbonate hemodialysis

Efficacy of the bicarbonate dialysate with acetate concentrations of 0-0.3 and 3-5: A systematic review and meta-analysis

INTRODUCTION

Acetic acid in dialysis fluid has been reported to induce symptomatic hypotension and post-dialysis fatigue. However, it remains unclear whether acetate-free dialysate improves these outcomes due to the lack of comprehensive evidence. This systematic review and meta-analysis aimed to compare the effects of acetate-free dialysate with standard acetate-containing dialysate using randomized controlled trials.

METHOD

We searched databases including MEDLINE, EMBASE, CENTRAL, and trial registries. Primary outcomes were fatigue, intradialytic hypotension (IDH), and all-cause mortality. Secondary outcomes included dropout rate due to adverse events, serum bicarbonate levels, and acid-base balance (pH) at the study's end. The Cochrane risk of bias tool 2 for crossover trials assessed the risk of bias, and we used a random effects model for meta-analyses, along with the GRADE approach to rate evidence certainty.

RESULTS

We identified four randomized crossover trials involving 114 patients, all at high risk of bias due to period and carryover effects. The studies showed no significant impact on fatigue. Acetate-free dialysate may slightly reduce IDH (OR 0.83, 95% CI 0.66 to 1.04; I2 = 79%, across two studies with 5872 sessions) with low certainty of evidence. Results for secondary outcomes, including bicarbonate levels and pH, were inconclusive due to very low certainty of evidence.

CONCLUSION

In conclusion, no clear benefit was observed for acetate-free dialysate compared with dialysate containing low concentrations of acetate. Further studies are needed to definitively ascertain the benefits of low-acetate dialysates in hemodialysis treatment.

Effect of time-dependent dialysate bicarbonate concentrations on acid-base and uremic solute kinetics during hemodialysis treatments

Recent studies have suggested benefits for time-dependent dialysate bicarbonate concentrations (Dbic) during hemodialysis (HD). In this clinical trial, we compared for the first time in the same HD patients the effects of time-dependent changes with constant Dbic on acid-base and uremic solute kinetics. Blood acid-base and uremic solute concentration were measured in twenty chronic HD patients during 4-h treatments with A) constant Dbic of 35 mmol/L; B) Dbic of 35 mmol/L then 30 mmol/L; and C) Dbic of 30 mmol/L then 35 mmol/L (change of Dbic after two hours during Treatments B and C). Arterial blood samples were obtained predialysis, every hour during HD and one hour after HD, during second and third treatments of the week with each Dbic concentration profile. Blood bicarbonate concentration (blood [HCO3]) during Treatment C was lower only during the first three HD hours than in Treatment A. Overall blood [HCO3] was reduced during Treatment B in comparison to Treatment A at each time points. We conclude that a single change Dbic in the middle of HD can alter the rate of change in blood [HCO3] and pH during HD; time-dependent Dbic had no influence on uremic solute kinetics.

Mathematical modelling of bicarbonate supplementation and acid-base chemistry in kidney failure patients on hemodialysis

Acid-base regulation by the kidneys is largely missing in end-stage renal disease patients undergoing hemodialysis (HD). Bicarbonate is added to the dialysis fluid during HD to replenish the buffers in the body and neutralize interdialytic acid accumulation. Predicting HD outcomes with mathematical models can help select the optimal patient-specific dialysate composition, but the kinetics of bicarbonate are difficult to quantify, because of the many factors involved in the regulation of the bicarbonate buffer in bodily fluids. We implemented a mathematical model of dissolved CO2 and bicarbonate transport that describes the changes in acid-base equilibrium induced by HD to assess the kinetics of bicarbonate, dissolved CO2, and other buffers not only in plasma but also in erythrocytes, interstitial fluid, and tissue cells; the model also includes respiratory control over the partial pressures of CO2 and oxygen. Clinical data were used to fit the model and identify missing parameters used in theoretical simulations. Our results demonstrate the feasibility of the model in describing the changes to acid-base homeostasis typical of HD, and highlight the importance of respiratory regulation during HD.

Replenishing Alkali During Hemodialysis: Physiology-Based Approaches

The acid-base goal of intermittent hemodialysis is to replenish buffers consumed by endogenous acid production and expansion acidosis in the period between treatments. The amount of bicarbonate needed to achieve this goal has traditionally been determined empirically with a goal of obtaining a reasonable subsequent predialysis blood bicarbonate concentration ([HCO₃^-]). This approach has led to very disparate hemodialysis prescriptions around the world. The bath [HCO₃^-] usually chosen in the United States and Europe causes a rapid increase in blood [HCO₃^-] in the first 1-2 hours of treatment, with little change thereafter. New studies show that this abrupt increase in blood [HCO₃^-] elicits a buffer response that removes more bicarbonate from the extracellular compartment than is added in the second half of treatment, a futile and unnecessary event. We propose that changes in dialysis prescription be studied in an attempt to moderate the initial rate of increase in blood [HCO₃^-] and the magnitude of the body buffer response. These new approaches include either a much lower bath [HCO₃^-] coupled with an increase in the bath acetate concentration or a stepwise increase in the bath [HCO₃^-] during treatment. In a subset of patients with low endogenous acid production, we propose reducing the bath [HCO₃^-] as the sole intervention.