TREATMENT CONSIDERATIONS IN CONVENTIONAL HD – WHAT WE KNOW Guest Editors: Csaba P. Kovesdy and Keiichi Sumida Dialysate bicarbonate concentration: Too much of a good thing? Carlo Basile 1,2 | Luigi Rossi 3 | Carlo Lomonte 3 1 Division of Nephrology, Clinical Research Branch, Miulli General Hospital, Acquaviva delle Fonti, Italy 2 Associazione Nefrologica Gabriella Sebastio, Martina Franca, Italy 3 Division of Nephrology, Miulli General Hospital, Acquaviva delle Fonti, Italy Correspondence Carlo Basile, Division of Nephrology, Miulli General Hospital, Acquaviva delle Fonti, Italy. Email: basile.miulli@libero.it 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 home- ostasis 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 alkalo- sis may contribute to adverse clinical outcomes. Unfortunately, no randomized stud- ies 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 summa- rizes our current state of knowledge in this field. For the present, the clinician should understand that target values for predialysis serum bicarbonate concentra- tions have been established primarily based on observational studies and expert opinion. On the basis of this information, we should keep predialysis serum bicar- bonate 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. 1 | INTRODUCTION The physiologic approach to assessing acid-base status views blood pH as being determined by the prevailing levels of carbonic acid (that is, PCO 2 , the respiratory component) and HCO 3 (the meta- bolic component, further indicated as BIC). 1,2 The standard blood gas analyzer measures pH and PCO 2 , from which BIC is calculated using the Henderson Hasselbalch equation. 1 Attributable to convenience and wide availability, directly measured serum total CO 2 (TCO 2 ) in venous blood is routinely used in screening for acid-base disorders in patients undergoing hemodialysis (HD). 2 The underlying rationale is that both metabolic and respiratory disorders (the latter by virtue of the secondary responses of BIC to changes in PCO 2 ) are associ- ated with abnormalities in BIC. Although the measured TCO 2 is almost always termed BIC, the two are not equivalent. Serum TCO 2 includes both BIC and dissolved CO 2 (TCO 2 = [HCO 3 ] + 0.03 9 PCO 2 ). Under most conditions TCO 2 is approximately 1 mEq/L higher than BIC when measured in the same blood sample. 3 Ideally, assessment of acid-base status in any patient should include blood pH and PCO 2 , with calculation of BIC. Unfortunately, the additional time (and cost) for this measurement in all our HD DOI: 10.1111/sdi.12716 Seminars in Dialysis. 2018;1–7. wileyonlinelibrary.com/journal/sdi © 2018 Wiley Periodicals, Inc. | 1