Even though a lot of people are familiar with the chemical and physical concepts of convection and diffusion, dialysis was carried generally through diffusion at first four decades. Hemodialysis (HD), ensures survival of a lot of patients with kidney disease globally and it has met increasing requirement generated in 50 year time since dialysis was given preference in case of renal replacement for long term.
There are a lot of reasons of economic and technological nature. Hemofiltration (HF) or hemodiafiltration (HDF) modalities calls for dialyzers use of high permeability and, at same time, it monitors with dual pump and volume control.
The replacement fluid is further cost, main reason to abandon HF, and it was key constraint on initial HDF technique with the volumes with range of 3 to 10L.
During 1990s, introduction of HDF techniques online through dialysis fluid as alternative solution has now meant revolution in the HD units.
Another 10 years were down the line for upgrading and renovating water treatment, introducing certain monitors and incorporating different safety filters for ensuring ultrapure dialysate.
European Dialysis working group (EUDIAL) has revisited hemodiafiltration definition (1) as treatment for blood clearance combining convective and diffusive transport through high-flux dialyzer with (KUF) > 20mL/mm Hg/h/m2 ultrafiltration coefficient, a ß2-microglobulin higher than 0.6 sieving coefficient, and effective convective transport percentage more than 20 percent blood. The convection volume is the sum of replacement volume and intradialytic loss of weight.
Requirement of systematic implementation of online hemodiafiltration
The online HDF (OL-HDF) gets indicated for all the patients who receive hemodialysis as no contradictions exist. The online HDF techniques can constitute of the progress towards the renal replacement therapy similar to native kidney. Such techniques provide high clearance of uremic substances having greater molecular range.
Possible clinical benefits provided by convection techniques mean much better hyperphosphatemia, anemia, inflammation, malnutrition, dialysis associated amyloidosis, insomnia, restless leg syndrome, irritability, polyneuropathy, intradialytic tolerance and itching.
Optimizing online hemodiafiltration
The best option is native fistula meant for all the HD modalities and also for the OL-HDF. However, using native graft and fistula decreased due to greater patient age and increase cardiovascular disease prevalence and diabetes. Using catheter results in connective volume and low blood flow (Qb).
In a multicenter study, only one third of catheters patients got minimum 21 L replacement volume target (11). This is vital for considering that the patients having catheters must increase dialysis duration for achieving adequate dialysis dose (additional 30 minute when catheter got used in normal position and an hour if it remains in reverse position (12). Therefore the use of catheter must be seen as obstacle for the HDF, but increase in duration of dialysis needs to be considered.
These new machines allow automatic flow of infusion (Qi) for maximizing convective volume that has reduced hemoconcentration risk and has increased convective volume (14-15).
A limiting issue for the convective volume is the Qb. The post dilution mode requires maximum flow of infusion of 33 percent Qb value. Getting adequate volumes becomes complicated in patients having limited Qb. According to some authors the Qb prescription is more of a treatment policy matter for each dialysis than patient characteristics.
Is it recommended to alter towards online hemodiafiltration?
There is plenty of science based evidence that supports the treatment increase overall and cardiovascular survival. Secondly, the technological water treatment development, monitor advances, and widespread use of synthetic high-flux dialyzers, make it a feasible choice. Also finally, with HDF online you get all possible clinical advantages, and any published literature isn’t available that presents any negative effects.
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