MP528BLOOD VOLUME MONITORING SYSTEMS : WHAT ARE WE MEASURING ?
Frank Le Roy, Mélanie Hanoy, B Perrone · Nephrology Dialysis Transplantation · 2017
INTRODUCTION AND AIMS: Increasing number of dialysis machines have embarked Blood Volume Monitoring Systems (BVMS) who allow displaying Relative Blood Volume (RBV) curve. RBV is calculated from hemoconcentration’s measurement either optical or ultrasonic.J Dasselaar et al. published (NDT 2005) : BVMS underestimates RBV values : -8.2% (BVMS) vs -17.3% (gold standard isotopic method). Values given by both methods however were identical during first hour of HD sessions then progressively diverged until session’s end.We thus conjectured : isotopic method and BVMS measure different blood volumes.On the other hand we have devised a simple hydraulic RBV model : with peak and trough filtration, both RBV curves (model displayed and BVMS observed) show identical peak and trough behaviour.We then conjectured : BVMS measures a volume whose vasculature has a much less complex architecture than global vasculature : this volume might be Central Blood Volume (CBV) METHODS: RBV variation (session’s end value - BVM System Fresenius) and CBV variation (session’s start vs end value - Transonic device measurement) were compared. Transonic measurement’s main purpose being cardiac output and total peripheral resistance survey.N= 20 patients (1 session each patient) Time on HD 5.2±4.5 years - Age 69.1±15 years - Body weight 63.9±12 Kg - Filtration during session : 2397±779 ml RESULTS: same variation was observed for RBV and CBV: RBV (BVMS) -12.4%±4.9 ; CBV (Transonic) -12.9%±8 [p= 0.75]. Correlation however was poor: RBV = 8.175+ 0.33*CBV [R2=0.346] CONCLUSIONS: BVMS seem to measure CBV variation and not total blood volume variation. Further study with higher number of sessions and same person for operating Transonic measurements is needed to confirm preliminary results.