34 The three most commonly used BVM devices, Crit-line, Haemoscan® and Fresenius® BVM, were compared with each other and to laboratory-derived BV changes (based on changes in haemoglobin).32 All three devices yielded values different from the laboratory-derived values and there was also significant variability between the three devices. This possibly reflects the different methods by which the changes in BV are acquired. Modulation of blood volume has been used to assess the different rates of UF on RBV. UF profiles and rates vary from constant, high at onset and isolated pulses. The highest rate of IDH was found in dialysis sessions where UF occurred in pulses or steps.35 Attempts

have been made to measure the changes in RBV over a

series of sessions and store this in the dialysis machine so that UF can be adjusted once the RBV reaches a patient-specific threshold. However, the check details Epigenetics inhibitor RBV adjusted for UF varies greatly between dialysis sessions reflecting different UF requirements.36 The more fluid overloaded a patient, the smaller the decrease in RBV per unit of UF volume.36,37 This technology has been expanded to create a preferred UF profile for an individual patient based on stored RBV measurements obtained from these patients. During HD the dialysis machine checks the RBV measurement against the stored profile and adjusts the UF rate and dialysate sodium concentration accordingly. This uses fuzzy logic principles, which aim to derive a definite conclusion from what is often imprecise or ambiguous data. This aims to mimic human decision making allowing a degree of flexibility not possible with mathematical modelling.38 After an initial successful single centre experience39 the biofeedback system technology Protirelin has been shown to reduce the incidence of IDH in several randomized trials.19,29,40 A recent study aimed to assess to utility of UF index (UF rates divided by post-dialysis weight), RBV slopes and volume

index (RBV slopes adjusted for UF rate and weight) in determining BV status in 150 difficult patients.41 While these were shown to be possible markers of volume status they did not predict the onset or frequency of IDH. The use of RBV slopes has been shown to be useful in the assessment of IBW in hypertensive HD patients.42 Various BVM technologies are now readily available; however, their utility in IDH remains unclear. BVM devices (especially with the addition of fuzzy logic systems) decrease the incidence of IDH in a at risk population; however, there is limited evidence that BVM can predict IDH in individual patients or that there is a long-term morbidity and mortality benefit, especially in the wider HD population. The technology is undergoing constant refinement, as is the interpretation and analysis of the RBV curves in relation to the other parameters such as weight, UF rate and sodium concentration.