nephrologists have always focused on serum bicarbonate concentration  as marker of metabolic acidosis. HCO3 concentration  has been associated to mortality risk in hemodialysis patients (U-shape curve relationship: see Bommer et al. and Wu et al). Concerns have been raised on changing bicarbonate level in dialysis bath (see, as an example Gennari et al). Please see also Tentori et al.

More recently Yamamoto el al (AJKD 2015)  failed to find relationship between serum HCO3 and mortality risk, however they found high pre-dialysis pH associated with increased risk of death in hemodialysis population.  

at the end of the story there are a lot of under-recognized respiratory disorders in hemodialysis population (see my paper in press on NDT).

In my opinion we should firstly categorize acid-base derangement in our dialysis patients. According to acid-base picture found then we can think how correct the disorder

(If you are interested in the topic, please feel free to ask me  full text of papers I cited above).

hope this is helpfull

As a practical approach, we use a bicarbonate of 32 mmol/l in dialysis bath to provide bicarbonte buffer moving from dialysate to the patient. Further, in Austria precursors of bicarbonate are available as oral medication, i.e. Acetolyt powder and in liquid form Lactat oral. These precursors require an adequate liver function to be metabolized to bicarbonate. Our aim is to keep actual bicarbonate (derived from arterial blood gas analysis) in the range of 24 +/- 2.

Metabolic acidosis in terminal chronic renal failure is harmful for the osteodystrophy, anemia, albumin synthesis and…

Of course, as previously discussed by Marco Marano and FC Prischl, high dialysate bicarbonate concentration is useful to correct metabolic acidosis.

I will focus on the interest of oral sodium bicarbonate supplementation during interdialysis process:

 500 ml by day of Eau de Vichy Celestins (1.5 g Na HCO3-) or sodium bicarbonate capsules. Patients are sometime reluctant for the taste, but many of them do not complain when the Eau de Vichy is cooled in a refrigerator. In contrary, a higher oral bicarbonate supplementation (more than 750 ml/d) may induce metabolic alkalosis…

 In contrast to NaCl, NaHCO3- does not induce hypertension or increase previously hypertension

(Hypertension 1991, 17 (sup1) I158 I161, Ann Intern Med 1983: Kotchen Ta, Kutz TW, NEJM 1987, 317, 1043-1048).

Moreover, oral bicarbonate supplementation may lower predialysis K+ levels and improve cardiac function  (ClinicalTrials.gov Identifier: NCT02692378).