Characterising fluid status, distribution and dynamics in haemodialysis patients to improve fluid management strategies

Both the removal of too much and the failure to remove enough fluid during haemodialysis are associated with morbidity and mortality. It has been suggested that bioimpedance measurements using the Body Composition Monitor (BCM) and relative blood volume (RBV) monitoring can improve fluid management. However, both lack a robust evidence base characterising measurements in the clinical setting. BCM measurements were made in healthy controls to characterise the effect of measuring outside standard conditions and were made alongside RBV measurements in haemodialysis cohorts with well-defined clinical characteristics that were perceived to influence BCM results. The results suggested that BCM protocols can be flexible regarding measurement paths and timing of measurement to ensure as many patients as possible can benefit from the technology. The observed tendency for patients with high body mass index (BMI) to finish dialysis fluid-depleted does not appear to be related to systematic bias in the BCM models, but to a greater tolerance of fluid removal. The tendency for elderly subjects to have a degree of excess fluid, as measured by BCM, does appear to be associated with changes in tissue hydration linked to sarcopenia. Standard measurements in patients with localised lower-limb oedema can lead to attempts to remove unrealistic fluid volumes and alternative paths can help optimise targets. Feasibility for a trial of interventions to promote fluid mobilisation from oedematous tissue was not demonstrated. Simultaneous use of RBV with BCM suggested that assumptions underlying current RBV shape analysis use for fluid management can be violated and that there is a need for further studies. BCM can be used across the haemodialysis population, but an understanding of its application in individuals with particular characteristics is essential. RBV provides complementary information to BCM but there is a need for re-evaluation of RBV interpretation, standardisation of measurement categorisation and development of intravascular volume measurements.