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Haemodiafiltration – The New Gold Standard?
a report by
and Dinna Cruz
1. Department of Nephrology, St Bortolo Hospital, Vicenza; 2. Division of Nephrology, Helsinki University Central Hospital
Haemodiafiltration (HDF) is a renal replacement technique combining simplified the procedure and reduced both operator workload and error.
diffusion and convection in order to enhance solute removal in a wide Neverthless, it remains a renal replacement modality used sporadically in
spectrum of molecular weights. It was first introduced by Henderson in Europe and never in North America.
In this modality, ultrafiltration exceeds the desired fluid loss
in the patient, and replacement fluid is administered to achieve Haemodiafiltration Variants
the target fluid balance. The relative contribution of convection to overall Since its original conception, various forms of HDF have evolved through
solute removal increases progressively with increasing molecular weight. the years (see Figure 1), from ‘classic’ HDF, to the more commonly utilised
‘online’ HDF, to variants using multicompartment filters such as ‘mid-
Technological developments in the fields of membranes, machines and dilution’ HDF. A brief description of different techniques is presented
fluids have contributed to making HDF a safe and effective technique. here; a more detailed review has been published.
First, synthetic polymer membranes with a combined hydrophilic–
hydrophobic structure and reduced wall thickness allowed a combination Classic Haemodiafiltration
of diffusive–convective techniques. Second, the development of accurate The classic HDF technique uses an average re-infusion rate of 9l/session
volumetric ultrafiltration control systems in dialysis machines reduced the (fluids contained in bags) in post-dilution (see Figure 1A). A blood flow
risk of fluid balance errors. Third, dialysis machines became equipped rate of over 300ml/minute is required for sufficient rates of ultrafiltration
with specific balancing systems to manage fluid re-infusion and at acceptable transmembrane pressure gradients. The equipment
ultrafiltration simultaneously. Next, online preparation of sterile and includes an ultrafiltration control system, a re-infusion pump and a scale
pyrogen-free solutions for infusion became possible, allowing the safe to weigh re-infusion bags.
The amount of re-infusion varied from
infusion of large fluid volumes during a HDF session.
Lastly, significant 3l/session (see Figure 1B, ‘soft’ HDF, e.g. biofiltration) to >15l/session (see
improvements in dedicated software and machine–user interfaces Figure 1C, ‘hard’ HDF, discussed below).
Claudio Ronco is Director of the Department of Nephrology
at St Bortolo Hospital in Vicenza. He is President of the
The acetate-free biofiltration form of HDF eliminates even small traces of
International Society for Hemodialysis (ISHD). He is a acetate from both dialysate and replacement fluid, which is titrated based
member of the council of several scientific societies and is
on blood bicarbonate level. This varies from six to nine litres per session.
Editor in Chief of the International Journal of Artificial
Organs. He has co-authored 650 papers, 36 book chapters,
45 books and seven monographic journal issues and has
delivered more than 450 lectures at international meetings
High-volume HDF is a specific form of classic HDF using a fluid exchange
minimum of 15l/session. A high ultrafiltration rate requires a high blood
flow, and replacement solution is often infused in pre-dilution mode.
Mikko Haapio is a Consulting Nephrologist at the Helsinki
While pre-dilution partially decreases the efficiency of the therapy, it
University Central Hospital (HUCH) and a Visiting Fellow in
the Department of Nephrology at St Bortolo Hospital in optimises blood flow distribution in the haemodialyser and a lower
Vicenzia. Previously, he worked in the Acute Dialysis Unit
protein concentration polarisation at the blood–membrane interface.
and the Nephrology Division. His principal areas of interest
are acute nephrology and cardio-renal syndrome. Dr Haapio
became a specialist in internal medicine in 2003 and in
nephrology in 2006.
The high cost of commercial replacement fluids (bags) stimulated the
development of online HDF, a novel technique (see Figure 1D). Fresh
ultra-pure dialysate from the dialysate inlet line is processed with multiple
Dinna Cruz is Co-ordinator of Scientific Research in the
Department of Nephrology at St Bortolo Hospital and the
filtration steps and re-infused as replacement fluid. Large amounts of
International Renal Research Institute in Vicenza, Italy. As a
inexpensive replacement solution are generated and HDF can be performed
nephrologist and epidemiologist, her research interests and
with a very high fluid turnover (up to 30–40l/session). Fluid can be re-infused
expertise include extracorporeal blood purification
techniques and acute kidney injury. She has published in either pre- or post-dilution mode (or both) in different proportions.
extensively on numerous aspects of renal disease in
prestigious international journals and has contributed
chapters to key international nephrology textbooks.
Internal Filtration Haemodiafiltration
The water flux in hollow fibre haemodialysers is characterised by a
proximal filtration and a distal backfiltration. Internal filtration HDF
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