Measurement of relative blood volume changes during haemodialysis: merits and limitations.

Dialysis hypotension is estimated to occur in 20% of haemodialysis (HD) sessions [1] and can lead to serious vascular complications such as cerebral infarction and cardiac and mesenteric ischaemia [2,3]. It may contribute to chronic overhydration due to an inability to reach dry weight and may lead to under-dialysis [1,2,4]. Prevention of dialysis hypotension, therefore, is an important challenge to the dialysis staff. The initiating factor in the pathogenesis of dialysis hypotension is a decrease in blood volume which results from the imbalance between the ultrafiltration rate and the plasma refilling rate [5]. Devices that continuously and non-invasively monitor relative blood volume (RBV) changes during HD are being advocated as a tool to maintain an adequate volume of the intravascular compartment in order to avoid dialysis hypotension [6–8]. Nowadays, most manufacturers have incorporated an RBV monitor in their dialysis apparatus, but evidence-based knowledge on how to use the RBV data in order to optimize the dialysis prescription of the individual patient is lacking. Moreover, there are conflicting data in the literature on the predictive value of RBV changes for the occurrence of dialysis hypotension. In this review, we will outline the pathophysiological response to ultrafiltration-induced reductions in blood volume, evaluate the RBVmeasuringmethods, discuss the relationship between RBV changes and blood pressure and discuss several factors that influence the validity of RBV measurements.