The "gold standard" method to evaluate the mass balances achieved during dialysis for a given solute remains total dialysate collection (TDC). However, since handling over 100 liter volumes is unfeasible in our current dialysis units, alternative methods have been proposed, including urea kinetic modeling, partial dialysate collection (PDC) and more recently, monitoring of dialysate urea by on-line devices. Concerned by the complexity and costs generated by these devices, we aimed to adapt the simple "gold standard" TDC method to clinical practice by diminishing the total volumes to be handled. We describe a new system based on partial dialysate collection, the continuous spent sampling of dialysate (CSSD), and present its technical validation. Further, and for the first time, we report a long-term assessment of dialysis dosage in a dialysis clinic using both the classical PDC and the new CSSD system in a group of six stable dialysis patients who were followed for a period of three years. For the CSSD technique, spent dialysate was continuously sampled by a reversed automatic infusion pump at a rate of 10 ml/hr. The piston was automatically driven by the dialysis machine: switched on when dialysis started, off when dialysis terminated and held during the by pass periods. At the same time the number of production cycles of dialysate was monitored and the total volume of dialysate was calculated by multiplying the volume of the production chamber by the number of cycles. Urea and creatinine concentrations were measured in the syringe and the masses were obtained by multiplying this concentration by the total volume. CSSD and TDC were simultaneously performed in 20 dialysis sessions. The total mass of urea removed was calculated as 58038 and 60442 mmol/session (CSSD and TDC respectively; 3.1 +/- 1.2% variation; r = 0.99; y = 0.92x -28.9; P < 0.001). The total mass of creatinine removed was 146,941,143 and 150,071,195 mumol/session (2.2 +/- 0.9% variation; r = 0.99; y = 0.99x + 263; P < 0.001). To determine the long-term clinical use of PDC and CSSD, all the dialysis sessions monitored during three consecutive summers with PDC (during 1993 and 1994) and with CSSD (1995) in six stable dialysis patients were included. The clinical study comparing PDC and CSSD showed similar urea removal: 510 +/- 59 during the first year with PDC and 516 +/- 46 mmol/dialysis session during the third year, using CSSD. Protein catabolic rate (PCR) could be calculated from total urea removal and was 1.05 +/- 0.11 and 1.05 +/- 0.09 g/kg/day with PDC and CSSD for the same periods. PCR values were clearly more stable when calculated from the daily dialysate collections than when obtained with urea kinetic modeling performed once monthly. We found that CSSD is a simple and accurate method to monitor mass balances of urea or any other solute of clinical interest. With CSSD, dialysis efficacy can be monitored at every dialysis session without the need for bleeding a patient. As it is external to the dialysis machine, it can be attached to any ty...
These findings are completely new and have clear applications in clinics. The vertex point might be used to define the optimal QUF of a dialysis system, which would be that obtained at KUF max and corresponds to the best QUF/transmembrane pressure ratio, as opposed to the maximum QUF (which corresponds to the highest possible QUF), frequently associated with haemoconcentration, clotting, loss in dialyser surface area, and treatment problems. Determining KUF max in vivo could be of help in dialysis prescription and control with automatic systems.
IntroductionRecent randomised controlled trials suggest that on-line hemodiafiltration (OL-HDF) improves survival, provided that it reaches high convective volumes. However, there is scant information on the feasibility and the consequences of modifying convection volumes in clinics.MethodsTwelve stable dialysis patients were treated with high-flux 1.8 m2 polysulphone dialyzers and 4 levels of convection flows (QUF) based on GKD-UF monitoring of the system, for 1 week each. The consequences on dialysis delivery (transmembrane pressure (TMP), number of alarms, % of achieved prescribed convection) and efficacy (mass removal of low and high molecular weight compounds) were analysed.ResultsTMP increased exponentially with QUF (p<0.001 for N >56,000 monitoring values). Beyond 21 L/session, this resulted into frequent TMP alarms requiring nursing staff interventions (mean ± SEM: 10.3 ± 2.2 alarms per session, p<0.001 compared to lower convection volumes). Optimal convection volumes as assessed by GKD-UF-max were 20.6 ± 0.4 L/session, whilst 4 supplementary litres were obtained in the maximum situation (24.5 ± 0.6 L/session) but the proportion of sessions achieving the prescribed convection volume decreased from 94% to only 33% (p<0.001). Convection increased high molecular weight compound removal and shifted the membrane cut-off towards the higher molecular weight range.ConclusionsReaching high convection volumes as recommended by the recent RCTs (> 20L) is feasible by setting an HDF system at its optimal conditions based upon the GKD-UF monitoring. Prescribing higher convection volumes resulted in instability of the system, provoked alarms, was bothersome for the nursing staff and the patients, rarely achieved the prescribed convection volumes and increased removal of high molecular weight compounds, notably albumin.
Background. Uraemic toxins in the 8 to 60 kDa molecular weight range have been attracting increasing attention in dialysis therapy. However, there are no available standardized methods to evaluate their removal. Using new filtering membranes, we evaluated SDS–PAGE of spent dialysate to assess cut-off ranges and removal capacities into dialysate, while also measuring classical markers of dialyser function.Methods. Eighteen dialysis patients were washed out for 2 weeks with FX 100 (Helixone®), followed by randomization to Xevonta Hi 23 (Amembris®) or FX dialysers for 2 weeks, then crossed over for an additional 2 weeks, and finally placed on Xenium 210 (Purema®) for 2 weeks. SDS–PAGE scanning of the removed proteins contained in the spent dialysate was performed during all dialysis sessions. Total mass of urea, creatinine, total proteins, beta 2 microglobulin (β2m), retinol-binding protein (RBP) and albumin were measured. The reduction rates of serum urea, creatinine, β2m, leptin, RBP, alpha 1-antitrypsin, albumin and total proteins were also determined.Results. SDS–PAGE scanning identified four major protein peaks (10–18, 20–22.5, 23–30 and 60–80 kDa molecular weight) and showed clear differences in the amounts of removed proteins between the dialysers, particularly in the 20–22.5, 23–30 and 60–80 kDa ranges. Total mass of removed β2m, RBP and albumin were in agreement with SDS–PAGE, while serum assays showed differing results.Conclusions. SDS–PAGE scanning provided a good characterization of protein patterns in the spent dialysate; it extended and agreed with protein determinations and allowed a better assessment of dialyser performance in removing 10 to 80 kDa molecular weight substances. It also identified differences between the three mainly filtrating polysulfone dialysers that were not detected with blood measurements.
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