Research Article: Consequences of increasing convection onto patient care and protein removal in hemodialysis

Date Published: February 6, 2017

Publisher: Public Library of Science

Author(s): Nathalie Gayrard, Alain Ficheux, Flore Duranton, Caroline Guzman, Ilan Szwarc, Fernando Vetromile, Chantal Cazevieille, Philippe Brunet, Marie-Françoise Servel, Àngel Argilés, Moglie Le Quintrec, Harald Mischak.


Recent 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.

Twelve 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.

TMP 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. Reaching 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.

Partial Text

Adding convection to standard haemodialysis was proposed in the sixties (haemofiltration) and seventies (hemodiafiltration (HDF)), to improve treatment performances [1,2]. Although the value of using convective over diffusive techniques has been debated for many years [3]. Three recent randomised controlled studies suggest a survival benefit associated with HDF, particularly when total convection volumes were high [4–6]. The Turkish study compared high flux haemodialysis with on-line HDF [4] while the Dutch CONTRAST [5] compared low flux haemodialysis with on-line HDF treated patients. Both studies only showed a survival benefit in post-hoc analyses that were not pre-specified (casting some doubt on their robustness). The Catalan ESHOL [6] only retained for analysis those patients with high convection volumes as per study design and observed a significant improvement in survival in HDF treated group. These reports may have participated in the wider use of HDF observed worldwide: OL-HDF, previously limited to 6.2% of the total hemodialysis has started increasing in Europe, and represents 10% in Australia and New Zealand [7–9]. The number of patients receiving HDF worldwide doubled between 2004 and 2010 [8].

Statistical analyses were performed using a SAS V9.2 (SAS Corporation, Cary, NC, USA). Differences in the continuous variables among the four different convection settings tested were assessed using an analysis of variance. Bonferroni’s test was used to check the differences between 2 of the 4 conditions. P values < 0.05 were considered significant. Values are given as mean ± standard error of the mean. The clinical characteristics of the 12 patients (6 males and 6 females) included in the study are presented in Table 1. Table 2 displays the dialysis characteristics and the performances in terms of convection volume obtained with the different treatment types. The total convection volumes obtained in optimal OL-HDF were 20.6 ± 0.4 L/session and 24.5 ± 0.6 L/session with maximum OL-HDF. Increasing convection resulted in hemoconcentration within the blood circuit with a filtration fraction (QUF/QB) of 3.2 ± 0.2, 14.8 ± 0.2, 23.9 ± 0.3 and 28.1 ± 0.4% (p<0.001) for HD, low, optimal and maximum convection OL-HDF respectively. Convection was sought from early sixties trying to establish a renal replacement system based upon a filtration process rather than upon a diffusion process, aiming to emulate the filtration process of the glomerulus in the “in vivo” situation [1,2]. The present study is the first controlled study designed to assess the effects of increasing convection in clinics and provides new data on the clinical feasibility and consequences of using high convection volumes in OL-HDF, a feature that the recent RCTs suggest is of crucial importance on seeking survival benefits in dialysis treatment [4–6].   Source:


0 0 vote
Article Rating
Notify of
Inline Feedbacks
View all comments