The SODIAH study is designed with the aim to assess the impact of isonatremic dialysis on interdialytic weight gain, fluid status, intradialytic hemodynamic stability, and incidence of intradialytic morbid events in dialysis patients. The study will be comparing the Na management option on the 6008 HD dialysis machines with the same machine without the Na management option turned on. Relevant performance and clinical data will be collected as well as information on patients' quality of life and wellbeing.

Inclusion Criteria:

General:

• Informed consent signed and dated by study patient and authorized physician
• Minimum age of 18 years
• The patient is legally competent and able to understand the nature, risks, meaning, and consequences of the clinical trial and can subsequently declare her/his consent for participation in the clinical trial
• Patients with a chronic kidney disease stage 5D (end stage renal disease with a glomerular filtration rate of 15 ml/min or less) on dialysis as extracorporeal renal replacement therapy.

Study-specific:

• Patients on dialysis (HD/HDF), at least 4h treatment time thrice weekly ≥ 3 months using a standard dialysate with a prescribed sodium concentration of 136 mmol/L
• Anuric patients (<300mL/d; 1 measurement within last 4 weeks)
• Patient fulfils one of the four following criteria:

interdialytic weight gain over 4% of dry weight (mean value during run-in period) OR pre-dialytic systolic blood pressure over 180 mmHg (mean value during run-in period) OR intradialytic morbid events (hypotension, hypertension, cramps, headache) in at least three sessions during run-in period OR volume overload according to BCM (FO ≥2.5 L pre-dialysis or relative FO pre-dialysis ≥15% for men and ≥13% for women; one measurement during run-in period)

- Patients with a diffusive Na load of at least 1 mmoL/(L TBW) or 0.06g NaCl/(L TBW) (mean value during the run-in period).

Exclusion Criteria:

General:

• Any conditions which could interfere with the patient's ability to comply with the study
• Patient is not able to give informed consent according to European Medical Device Regulation and corresponding national regulations
• In case of female patients: pregnancy (pregnancy test will be conducted at start and end of study with female patients aged ≤55 years) or lactation period
• Participation in an interventional clinical study during the preceding 30 days
• Previous participation in the same study

Study-specific:

• Patients treated with individualized sodium management over the last 3 months
• Severe hypoalbuminemia (≤30 g/L; 1 measurement within last 4 weeks)
• Hypernatremia (pre-dialytic plasma sodium concentration ≥145mmol/L; 1 measurement within last 4 weeks)
• Uncontrolled diabetic patients with glycated hemoglobin (HbA1C) >8%; 1 measurement within last 4 weeks
• Impossible reliable measurement of the different compartments by bioimpedance due to lower limb amputation or wearing of a unipolar pacemaker or metallic prostheses
• Life expectancy less than 6 months
• ONLINEplus HF treatments/hemofiltration treatments
• Single-needle treatments
• Dry weight < 40kg
• Active or chronic infections (HIV, SARS-CoV-2, HBV, HCV)