Hemodialysis using a low bicarbonate dialysis bath: Implications for acid-base homeostasis.

The low bath bicarbonate concentration ([ HCO 3 - ]) used by a nephrology group in Japan (25.5 mEq/L), coupled with a bath [acetate] of 8 mEq/L, provided an opportunity to study the acid-base events occurring during hemodialysis when HCO 3 - flux is from the patient to the bath. We used an analytic tool that allows calculation of HCO 3 - delivery during hemodialysis and the physiological response to it in 17 Japanese outpatients with an average pre-dialysis blood [ HCO 3 - ] of 25 mEq/L. Our analysis demonstrates that HCO 3 - addition is markedly reduced and that all of it comes from acetate metabolism. The HCO 3 - added to the extracellular fluid during treatment (19.5 mEq) was completely consumed by H+ mobilization from body buffers. In contrast to patients dialyzing with higher bath [ HCO 3 - ] values in the US and Europe, organic acid production was suppressed rather than stimulated. Dietary analysis indicates that these patients are in acid balance due to the alkaline nature of their diet. In a larger group of patients using the same bath solution, pre-dialysis blood [ HCO 3 - ] was lower, 22.2 mEq/L, but still in an acceptable range. Our studies indicate that a low bath [ HCO 3 - ] is well tolerated and can prevent stimulation of organic acid production.