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.