Pilot Trial of Oral Sodium Bicarbonate Versus Higher Dialysate Bicarbonate in Hemodialysis Patients With Metabolic Acidosis

Metabolic acidosis is frequent in chronic hemodialysis patients and is associated with adverse clinical outcomes. Two commonly used strategies to correct acidosis are oral sodium bicarbonate supplementation and increasing the bicarbonate concentration of the dialysate, but their comparative effectiveness and tolerance in routine care remain uncertain. This pilot, prospective, randomized, open-label, two-center trial will compare oral sodium bicarbonate versus higher dialysate bicarbonate in chronic hemodialysis patients with metabolic acidosis, using predialysis plasma bicarbonate concentrations, so-called "reserves alcalines" or "alkaline reserves" in local laboratory reports, as a pragmatic marker of acid-base status. Approximately 30 acidotic patients (serum bicarbonate \< 22 mmol/L) will be randomized 1:1 to receive either oral sodium bicarbonate or an increase in dialysate bicarbonate for 4 weeks; an additional non-acidotic observational group will provide descriptive reference data. The primary outcome is the change in predialysis serum bicarbonate from baseline (Day 0) to Day 28 between the two randomized arms. Secondary outcomes include the proportion of patients reaching target serum bicarbonate levels, the weekly kinetics of correction, dialysis adequacy (Kt/V and online clearance monitoring), intradialytic tolerance (blood pressure, cramps, hypotension, symptoms), and sodium-related safety (natremia, interdialytic weight gain). Feasibility indicators such as recruitment, retention, adherence to treatment and dialysate adjustment, and data completeness will also be described to inform the design of a larger definitive trial.

Inclusion Criteria: * Age ≥ 18 years. * Chronic hemodialysis for at least 3 months. * Stable hemodialysis prescription (no major change in dialysis prescription in the previous weeks, as per local practice). * Predialysis low "alkaline reserves" (serum bicarbonate concentration) according to the operational threshold used in the unit (e.g., "alkaline reserves" \< 22 mmol/L), consistent with KDIGO 2017 definition of metabolic acidosis. * Ability to give written informed consent. For the observational group: * Age ≥ 18 years. * Chronic hemodialysis for at least 3 months. * Predialysis "alkaline reserves" considered stable and within the locally defined normal range (≥ 22mmol/L). * Ability to give written informed consent. Exclusion Criteria: * Recent hemodynamic instability (e.g., repeated intradialytic hypotension or unstable blood pressure in the previous weeks). * Recent hospitalization for an acute condition. * Acute infection or major intercurrent acute event at the time of screening. * Major change in dialysis prescription in the 2 weeks prior to inclusion (e.g., change in dialysis schedule, duration, or dialysate composition outside the study protocol). * Severe digestive disorders limiting oral intake (e.g., persistent vomiting, severe malabsorption, or any condition preventing safe oral Bicardis administration). * Known hypernatremia or high risk of uncontrolled sodium and fluid overload (as judged by the investigator). * Severe uncontrolled hypercalcemia or hypocalcemia. * Any condition that, in the investigator's judgment, would preclude safe participation or interfere with study procedures (e.g., very limited life expectancy, inability to attend scheduled visits). * Refusal to participate or inability to provide written informed consent.