Dialysate bicarbonate concentration: Too much of a good thing?

Abstract

Acid-base equilibrium is a complex and vital system whose regulation is impaired in chronic kidney disease (CKD). Metabolic acidosis is a common complication of CKD. It is typically due to the accumulation of sulfate, phosphorus, and organic anions. Metabolic acidosis is correlated with several adverse outcomes, such as morbidity, hospitalization and mortality. In patients undergoing hemodialysis, acid-base homeostasis depends on many factors: net acid production, amount of alkali given by the dialysate bath, duration of interdialytic period, as well as residual diuresis, if any. Recent literature data suggest that the development of postdialysis metabolic alkalosis may contribute to adverse clinical outcomes. Unfortunately, no randomized studies exist about the effect of different dialysate bicarbonate concentrations on hard outcomes, such as mortality. Like everything else in dialysis, the quest for the "ideal" dialysate bicarbonate concentration is far from over. The Latin aphorism "ne quid nimis" ie "nothing in excess" (excess of neither acid nor base) probably best summarizes our current state of knowledge in this field. For the present, the clinician should understand that target values for predialysis serum bicarbonate concentrations have been established primarily based on observational studies and expert opinion. On the basis of this information, we should keep predialysis serum bicarbonate concentrations at least at 22 mEq/L. Furthermore, a specific focus should be addressed to the clinical and nutritional status of the major outliers on both the acid and alkaline sides of the curve.

Clinical practice guideline on undernutrition in chronic kidney disease

“…Acidosis is an established catabolic factor [36] and the bicarbonate concentration of patients on peritoneal dialysis and HD patients should be maintained within target range to minimise this [37]. Recent data suggests that predialysis serum bicarbonate levels of > 28 mmol/l may be associated with adverse outcomes [38]. Bicarbonate supplementation in the low clearance clinic may retard the progression of kidney disease [39].…”

Dialysis-Induced Cardiovascular and Multiorgan Morbidity

“…Another important contributor to systemic stress is the magnitude of solute fluxes. [140][141][142][143] Reducing instantaneous solute fluxes while keeping total solute mass transfer equivalent to attain dialysis adequacy goals is an important target to improve dialysis tolerance and to reduce patient burden. One approach is to reduce blood flow and increase treatment time and/or frequency (e.g., nocturnal dialysis, alternate day, or daily dialysis) in order to compensate for the reduction of instantaneous solute fluxes.…”

“…169 Such tools could also be combined with approaches to reduce instantaneous solute fluxes while keeping total solute mass transfer and dialysis adequacy equivalent in an attempt to reduce intradialytic morbidity. [140][141][142][143] It is clear from past experience that a one-size-fits-all approach to reducing the physiological stresses of dialysis does not work. It is important to keep this in mind when novel developments in dialysis treatment are considered.…”

Total Carbon Dioxide Versus pH for Determining Acid-Base Status in Patients on Continuous Kidney Replacement Therapy: A Cohort Study

“…Blood gas analysis is the gold standard for determining acid-base status but is often omitted in clinical practice. 1 Serum bicarbonate (measured as total carbon dioxide [tCO 2 ]) is often used to evaluate acid-base status; alkalemia and acidemia are inferred from high and low tCO 2 levels, respectively. 2 We recently showed in patients receiving maintenance hemodialysis that compared to pH, 15% of inferences about acid-base status using tCO 2 measures were incorrect.…”