On-line urea kinetics in haemodiafiltration |
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Authors: | Santoro, A. Tetta, C. Mandolfo, S. Arrigo, S. Berti, M. Colasanti, G. D'Amico, G. Imbasciati, E. Mazzocchi, C. Pacini, G. Spongano, M. Thomaseth, K. Wratten, M. L. Zucchelli, P. |
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Affiliation: | 1Divisione di Nefrologia e Dialisi, Ospedale S.Orsola-Malpighi Bologna (I) 2Bellco S.p.A Mirandola (I) 3Servizio di Nefrologia e Dialisi Ospedale di Lodi (I) 4Divisione di Nefrologia e Dialisi, Ospedale S. Carlo Milano (I) 5Istituto di Sistemistica e Bioingegneria, Ladseb-Consiglio Nazionale delle Ricerche Padova (I) |
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Abstract: | BACKGROUND.: Calculation of Kt/V and assessment of nutrition have so farbeen dependent upon off-line urea measurements of blood or dialysatesamples. Here we describe a biosensor for on-line urea measurementduring haemodiafiltration. METHODS.: The biosensor consisted of a cartridge containing covalentlylinked urease placed between two conductivity cells. The biosensorwas placed on the outlet line of a haemofilter in series witha dialyser in order to obtain an aliquot of plasma ultrafiltratefor on-line measurement of urea. RESULTS.: Urea nitrogen concentrations were highly correlated to the difference() in conductivity measured by the two conductivity cells bothin aqueous solutions (in-vitro studies, y=6.676+32.12x,R2=0.998, P<0.0001) and in ultrafiltrates (ex-vivo studies,y=6.7+32.01x, R2=0.98, P<0.00001). conductivity washighly reproducible (% variation: 0.85.3%) and stable(maximal % variation at 150 mg/dl after 180 min: 0.9±0.3vs initial values). The intradialytic plasma water urea profilewas obtained in 10 haemodialysis patients. To study recirculation,the plasma water urea profile was analysed before and 3 minafter stopping the dialysate flow. The pre- and post-stoppedflow ratio (1.21±0.1, mean±1 SD) was superimposableto conventional blood sampling data (opposite arm venous/arterial:1.22±0.11) and allowed correction for recirculation.A novel approach to urea kinetic modelling was described andused to reliably project end-dialysis and post-dialysis reboundurea concentration as early as 90 min. Projected (29.2±10.4g) or measured (29.8±10.5 g) net urea removal was highlycorrelated with the amount of urea collected in the total spentdialysate (29.7±10.6 g) (R2=0.99, R2=0.97 respectively). CONCLUSIONS.: These results indicate that on-line, real-time analysis of ureakinetics may provide information on delivery of adequate dialysisin high-efficiency techniques. |
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Keywords: | biosensor haemodialysis mathematical modelling on-line monitoring recirculation urea kinetics |
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