Technical aspects of hemodiafiltration
- James Tattersall, MD, MRCP
James Tattersall, MD, MRCP
- Specialty Doctor in Renal Medicine
- Leeds Teaching Hospitals Trust
- Peter J Blankestijn, MD
Peter J Blankestijn, MD
- Associate Professor in Nephrology
- University Medical Center, Utrecht, The Netherlands
Hemodiafiltration (HDF) is a form of renal replacement therapy that utilizes convective in combination with diffusive clearance, which is used in standard hemodialysis. Compared with standard hemodialysis, HDF removes more middle-molecular-weight solutes. Some, though not all, studies have suggested that HDF is associated with improved clinical outcomes, providing adequate convection volumes are achieved.
However, HDF is more complex than standard hemodialysis and places increased demands on the user and outpatient dialysis center. HDF is not available in the United States. In Europe, Japan, and some other countries where HDF is available, most clinicians use a specific type of HDF termed online HDF. In online HDF, the substitution fluid is produced by the dialysis machine, which enables large convection volumes.
This topic reviews the technical aspects of HDF. Dosing recommendations and clinical outcomes for HDF are discussed elsewhere. (See "Chronic intermittent high-volume hemodiafiltration".)
Overview — Conventional hemodialysis clears uremic toxins mostly by diffusion driven by the thermal energy of the uremic toxin molecule. Clearance of the toxin by diffusion is inversely proportional to the radius of the toxin molecule. As a result, conventional hemodialysis clears larger toxin molecules less effectively than smaller ones. Clearance of larger toxins is limited by their low rate of diffusion, even if they can easily pass through the pores in the dialyzer membrane.
In contrast, hemodiafiltration (HDF) increases the clearance of larger toxins by large-volume ultrafiltration. Ultrafiltration carries toxins through the membrane pores by fluid flow, also known as convection. As long as the toxin molecule can easily pass through the membrane pores, the rate of transfer is independent of the molecule size.
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