Urea as a marker of adequacy in hemodialysis: Lesson from in vivo urea dynamics monitoring

• Published in: Kidney international Vol. 58; no. S76; pp. S28 - S40
• Main Authors: Canaud, Bernard, Bosc, Jean-Yves, Cabrol, Laurent, Leray-Moragues, Hélène, Navino, Carlo, Verzetti, Guiseppe, Thomaseth, Karl
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.08.2000; Elsevier Limited
• Subjects: Adult; Aged; Biomarkers; dialysis adequacy; Dialysis Solutions - administration & dosage; end-stage renal disease; Female; hemodiafiltration; Hemodiafiltration - methods; Hemodiafiltration - standards; Humans; intracorporeal urea mass transfer coefficient; Kidney Failure, Chronic - blood; Kidney Failure, Chronic - therapy; kinetic modeling of urea; Kinetics; Male; Middle Aged; Models, Biological; Point-of-Care Systems; Proteins - metabolism; Treatment Outcome; Urea - blood; dialysis adequacy; intracorporeal urea mass transfer coefficient; end-stage renal disease; kinetic modeling of urea; hemodiafiltration
• ISSN: 0085-2538; 0098-6577; 1523-1755
• DOI: 10.1046/j.1523-1755.2000.07604.x

Urea as a marker of adequacy in hemodialysis: Lesson from in vivo urea dynamics monitoring. “Dialysis dose,” a concept developed by Sargent and Gotch based on urea kinetic modeling, is a useful and recognized tool that is used to quantitate and optimize a dialysis-efficacy program. However, it has been shown that oversimplification of the “dialysis adequacy” concept to the Kt/V index might lead to dramatic underdialysis and subsequent deleterious consequences on morbidity and mortality of dialysis patients. With this perspective, the determination of Kt/V must be very cautious and rely on accurate measurement of postdialysis urea concentration and its use integrated as a tool in a quality-assurance process. In this study, we analyzed urea dynamics by means of a blood side (ultrafiltrate) continuous online urea monitoring system interfaced with a two-pool model hosted in amicrocom puter. The study was designed to provide instantaneous dialysis performances (body and dialyzer clearances, dialyzer mass transfer coefficient) and to determine the in vivo functional permeability characteristics of the patient [intercompartment urea mass transfer coefficient (Kc)]. Thirteen end-stage renal disease patients (age 54 ± 16 years; 12 male and 1 female) were studied during nine consecutive dialysis sessions (3 weeks). Urea kinetics obtained from the urea monitoring system fitted closely the urea kinetic modeling prediction, confirming the validity of the double-pool model structure. Effective in vivo urea mass transfer coefficient averaged 912 ± 235 mL/min/1.73 m2, a value close to those reported with more invasive methods. Large variations ranging from 363 to 1249 mL/min were observed among patients, confirming very large interindividual patient permeability differences. Interestingly, the urea mass transfer coefficient was inversely correlated with the postdialysis rebound values. Intraindividual variations were also noted as a function of time denoting functional changes in urea mass transfer coefficient values. The urea distribution volume was 38.1 ± 7, 8 L (53 ± 8% body weight). V1 referring to the extracellular volume and V2 to the intracellular volume were 9 ± 2L (13 ± 2% body weight) and 29.2 ± 6.6 L (41 ± 1.3% body wt), respectively. The extracellular/intracellular volume ratio was 0.31 (approximately one third) and was not as usually defined by the paradigm 1/2 ratio. Online double-pool urea kinetic modeling gavea new insight in urea kinetic modeling approach. Urea dynamics fit perfectly a double-compartment model structure. Accessible extracellular volume to hemodialysis is smaller than expected. The in vivo urea mass transfer coefficient must be considered as an individual and variable characteristic of ESRD patients that should be taken into consideration when prescribing the hemodialysis schedule.