title: Concordance of absolute and relative plasma volume changes and stability of Fcells in routine hemodialysis.
abstract: Central hematocrit (H) measurements are currently used to track the degree of ultrafiltration-induced hemoconcentration with the aim to detect and prevent excessive intravascular fluid depletion during hemodialysis (HD). Failure to maintain hemodynamic stability is commonly attributed to the misinterpretation of H caused by an unaccountable increase in Fcells , the ratio of whole-body hematocrit to H. It was the aim to examine Fcells under everyday conditions in a group of stable HD patients. Absolute plasma volume (Vp ) and H were concomitantly measured during routine HD in the extracorporeal system in hourly intervals by noninvasive and continuous technology (CritLine-Instrument-III) and indocyanine green dye dilution to derive relative plasma volumes from Vp and H (RPVp , RPVH ), respectively, and to calculate Fcells . Thirteen patients were studied during two midweek treatments (n = 26). Both absolute Vp (P < 0.05) and relative plasma volumes RPVH (P < 0.001) decreased during HD. Vp at any time point was positively correlated to RPVH (r = 0.52). Moreover, relative plasma volumes RPVH and RPVp determined by independent techniques were identical and showed negligible bias (-0.2%) but considerable limits of agreement (-15.6% to +15.3%). Fcells was stable and in the range of 0.9 ± 0.05 throughout HD and not different from the value assumed at the beginning of HD. Although Fcells remains constant in patients on routine dialysis and relative plasma volumes (RPVH and RPVp ) determined by independent techniques are therefore comparable, the variability of experimental conditions during dialysis and the limited accuracy of absolute volume measurements using available technology continues to complicate the ultrafiltration control problem.
authors.affiliation: Institute of Physiology, Medical University of Graz, Graz, Austria.
authors.forename: Daniel
authors.initials: D
authors.lastname: Schneditz
authors.affiliation: Clinical Division of Nephrology, Medical University of Graz, Graz, Austria.
authors.forename: Werner
authors.initials: W
authors.lastname: Ribitsch
authors.affiliation: Clinical Division of Nephrology, Medical University of Graz, Graz, Austria.
authors.forename: Gernot
authors.initials: G
authors.lastname: Schilcher
authors.affiliation: Institute of Physiology, Medical University of Graz, Graz, Austria.
authors.forename: Matthias
authors.initials: M
authors.lastname: Uhlmann
authors.affiliation: Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, MA, USA.
authors.forename: Yossi
authors.initials: Y
authors.lastname: Chait
authors.affiliation: Division of Gastroenterology, Department of Internal Medicine, Medical University of Graz, Graz, Austria.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Stadlbauer
mesh_terms: D005260:Female; D006400:Hematocrit / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010953:Plasma Volume / Q000502:physiology*; D006435:Renal Dialysis / Q000379:methods*; D014462:Ultrafiltration / Q000379:methods*
keywords: Ultrafiltration; hematocrit; monitoring; plasma volume