Background: Haemodynamic instability during haemodialysis has long been linked to poor cardiovascular outcomes. It does not always reflect overall hydration but rather plasma volume depletion, with a delay in plasma refill from other body compartments, and vasodilatation, mediated by endothelial factors. Our understanding of these processes remains largely incomplete. Despite our ability to monitor relative blood volume during haemodialysis our knowledge concerning the factors affecting plasma refill remain incomplete. This may be due to variations observed between individuals. Understanding the pattern of fluid shifts variation between the different body compartment and the factors affecting these behaviours in different individuals or at different hydration states could be a vital component of our management of intradialytic haemodynamic instability but also overhydration.

Aims and Objectives: The aim of this study is to describe plasma refill rate, during haemodialysis using a non-invasive, continuous, real-time data capture during ultrafiltration. The study will attempt to describe different refilling phenotypes in the study population and seek association with biochemical and haematological parameters linked to variability in refilling rates.

Methodology: This study will attempt to describe variations in the plasma refill rate of prevalent dialysis patients during their normal haemodialysis treatment and during a session of 3 hours of haemodialysis preceded by 1 hour of isolated ultrafiltration using the in-built blood volume monitoring module of their haemodialysis machine and the TMON software that collects continuous, real-time data by interfacing with the computer network. To achieve this, a bolus of 100-300ml of intravenous dialysis replacement fluid will be administered at the beginning of each of the 2 studied sessions.

Inclusion Criteria:

• Prevalent haemodialysis patient at CMFT and satellite units

Exclusion Criteria:

• Withdrawal of consent.
• Inability to provide informed consent.