The main objective is to establish a statistical predictive model of the risk of intradialytic hypotension during hemodialysis (HD) or hemodiafiltration (HDF) sessions based on the measurement of residual blood volume and excess extracellular hydration. The secondary objective is to study the impact of dysfunction in the mechanisms of compensation for decreased blood volume (heart disease, neuropathy, drugs) on the risk of intradialytic hypotension.

The duration of the study is 4 weeks for each patient. It will first be carried out a spectral analysis of heart rate variability (CHU of Clermont Ferrand only) and a measurement of intracellular and extracellular volumes by bioimpedancemetry. During the next 9 sessions, the decrease in the VSR will be recorded using an optical haematocrit measurement system. Blood pressure and heart rate will be measured every 30 minutes using an automatic blood pressure monitor and whenever the patient's nurse deems it necessary.

Inclusion Criteria:

• 18 years old minimum patients
• Patients with chronic end-stage renal failure
• Patients treated with hemodialysis for at least 3 months, 3 times a week (duration of sessions 3 to 5 hours)
• Patients with at least 2 episodes of intradialytic hypotension in the last month
• Patients without acute events within 3 months prior to inclusion
• Patients affiliated with or receiving social security benefits

Exclusion Criteria:

• Hemoglobin levels outside the limits of measurement (<7 g/L or >15g/L)
• Patients whose probable survival does not exceed 6 months
• Patients with progressive acute pathology
• Patient following another research protocol that may influence results
• Patients with psychiatric pathology or cognitive impairments that make them unable to give informed consent

Patients with chronic end-stage renal failure