Friday, 17 February 2012 03:13

HDF – A new and better dialysis?

Written by  Greg Collette
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There is a change blowing through the dialysis world.  Until recently, we BigD club members have belonged to either the haemodialysis branch, or the peritoneal dialysis branch.  But for some time now, there has been a third branch, HaemoDiaFiltration, or HDF and it may just be the leap in technology we have been waiting for.

HDF is a souped-up version of haemodialysis.  It has been around in Europe for many years, but until recently, it has been fiddly to set up and expensive.  But things are changing and most new machines will do either haemodialysis of HDF.

What’s the difference?

First a little theory.  We kidney-challenged individuals experience a constant build up of toxins as a part of everyday life (eating, drinking, exercising, etc,).  These would normally be extracted and excreted by our kidneys, but because they have left the building, we use dialysis machines to do much of this job for us.  The toxins come in two broad sizes: large molecule and small molecule.

A haemodialysis machine works by using pressure to filter water from our blood through a membrane (the “artificial kidney” on the front of each machine).  Once through the membrane, the water mixes with dialysate fluid on the other side.  At the same time, many of the small toxin molecules in the blood diffuse through the membrane into the dialysate liquid.  The dialysate is then discarded (and those little toxins with it).

Unfortunately, the large toxin molecules are too big to go through the membrane.  So they hang around, eventually doing damage.  One of the most famous is beta-2-microglobulin which builds up in the blood, forming a few very large molecules.  This is relatively common in older BigD members, who have been on dialysis for more than 5 years.  The result is pain, stiffness, and fluid in the joints (like my knee!).  About 50 percent also develop carpal tunnel syndrome.  No news there.

So what of HDF?  A HDF machine works in two ways.  First, like a haemodialysis machine, it removes small toxin molecules.  Second, it uses a more porous membrane to filter the blood, and a higher water flow on the other side of the membrane.  This has two effects: the membrane filters larger toxin molecules from the blood and the faster water flow draws more of the water from the blood, removing even more toxins.  It is a complex process because it removes a lot more water from the blood than is required to reach dry weight.  To offset this, the machine calculates and adds the required amount of replacement fluid into the arterial line before it reaches the membrane.  The new HDF – dialysis machines do this automatically.

The benefits of HDF are not immediate, and some medicos are sceptical, but if I have the choice between storing up large toxin molecules on haemodialysis or dumping them on HDF, I choose HDF.  Unfortunately, no treatment can get rid of the large molecules already embedded on my bones, joints and tissue.  But it will slow or stop more being added.  And people starting HDF BigD today, they may never have the problem.

HDF went out of fashion for the last decade or so because of the complexity and cost.  Technology improvements mean it is now on the rise many countries through Europe and in Australia (though not in the US where being more expensive that dialysis, it is virtually unavailable).

While it is more expensive, some dialysis organisations and units are beginning to offer it because it has the potential to dramatically improve the quality of life for BigD-ers.

My Diaverum unit is now offering it to everyone who meets what are fairly simple criteria: patients should be relatively young and be facing the prospect of long-term dialysis (ie, not getting a transplant within a year or two).  Most of us meet these criteria.  Currently they have only two HDF machines, so we will be sharing, but all replacements machines will be HDF capable.  So in a year or two, everyone will be able to have HDF on every run.

I have had all of one run on HDF, and all is well so far.  One big benefit is that HDF is much gentler on the heart, I had less of the last-hour nerves and didn’t feel quite so hyped up when I come off –  I slept well only an hour after I finished.   Some others in the unit have been on it for weeks and say they feel much improved, lower blood pressure, no jiggly legs and generally feeling healthier.  Whether this is real or imaginary, based on what they expect to happen, who knows?

I don’t know if this is a leap in technology, or a small step forward, but I look forward to finding out.

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Greg Collette

Greg Collette

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