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

Abstract

The low bath bicarbonate concentration ([HCO3-]) 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 HCO3- flux is from the patient to the bath. We used an analytic tool that allows calculation of HCO3- delivery during hemodialysis and the physiological response to it in 17 Japanese outpatients with an average pre‐dialysis blood [HCO3-] of 25 mEq/L. Our analysis demonstrates that HCO3- addition is markedly reduced and that all of it comes from acetate metabolism. The HCO3- 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 [HCO3-] 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 [HCO3-] was lower, 22.2 mEq/L, but still in an acceptable range. Our studies indicate that a low bath [HCO3-] is well tolerated and can prevent stimulation of organic acid production.

A New Approach to Bicarbonate Addition During Hemodialysis: Testing Model Predictions in a Patient Cohort

“…With our protocol, we see that I a is about 55% of the total alkali addition I, whereas in our prior study this percentage was only of 35%. This is a substantial improvement [4], [52].…”

“…We enrich the model developed in [4], [9], [10] with a differential equation for lactate dynamics during hemodialysis. Lactate generation and loss are calculated from the change in measured blood lactate concentration during dialysis using an equation that assumes first order kinetics [52]. The physical basis for the concentration of lactate in the patient's blood, denoted by C (t) (mmol/L), consists of internal (cellular) production P (mmol/min) of lactic acid (instantly converted into lactate) and a loss from a fixed volume V (L), through a membrane of "conductance" D (L/min) that connects the volume with an external void compartment (dialysis bath).…”

Acid–base balance in hemodialysis patients in everyday practice

“…Sargent et al. also reported that reducing bath HCO 3 – should decrease organic acid production [ 42 , 43 ].…”

Replenishing Alkali During Hemodialysis: Physiology-Based Approaches

“…Sargent's analysis avoids this entire controversy because it is based on an empirically measured value for bicarbonate dialysance that includes all the components of bicarbonate entry 18 . Using his model to analyze the acid-base events during hemodialysis in three patient studies, we found that Sargent's dialysance predicts the pattern of change in blood [HCO3 -] very well 6,8,19 . To the extent that the Sargent model overestimates bicarbonate influx because it fails to J o u r n a l P r e -p r o o f 7 consider a drop in dialysance, the calculated H + addition (buffer response) to the ECF would be overestimated.…”

“…The National Kidney Foundation guidelines for the recommended predialysis blood [HCO3 -] are from over 20 years ago and do not take these more recent studies into account 4 . Thus, this empiric approach has an uncertain goal and, as a result, bath [HCO3 -] varies widely in countries around the world, ranging from as low as 25 mmol/L in Japan to as high as 35 -40 mmol/L in the United States 1,5,6 . In Europe the most common values are in between the two extremes (32 -35 mmol/L) 1 .…”