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

Abstract

Dialysis hypotension is estimated to occur in 20% ofhaemodialysis (HD) sessions [1] and can lead to seriousvascular complications such as cerebral infarctionand cardiac and mesenteric ischaemia [2,3]. It maycontribute to chronic overhydration due to an inabilityto 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. Theinitiating factor in the pathogenesis of dialysis hypo-tension is a decrease in blood volume which resultsfrom the imbalance between the ultrafiltration rate andthe plasma refilling rate [5]. Devices that continuouslyand non-invasively monitor relative blood volume(RBV) changes during HD are being advocated as atool to maintain an adequate volume of the intravas-cular compartment in order to avoid dialysis hypo-tension [6–8]. Nowadays, most manufacturers haveincorporated an RBV monitor in their dialysis appa-ratus, but evidence-based knowledge on how to use theRBV data in order to optimize the dialysis prescriptionof the individual patient is lacking. Moreover, there areconflicting data in the literature on the predictive valueof RBV changes for the occurrence of dialysis hypoten-sion. In this review, we will outline the pathophysio-logical response to ultrafiltration-induced reductionsinbloodvolume,evaluatetheRBVmeasuringmethods,discuss the relationship between RBV changes andbloodpressureanddiscussseveralfactorsthatinfluencethe validity of RBV measurements.