Hemodialysis vs. Hemodiafiltration....the future..or another fad ?

[Dr. Evil]

This is a BRIEF overview of the difference between Hemodialysis vs. Hemodiafiltration.  This is not a textbook in-depth discription.  If someone with a lot of technical knowlege finds something I glossed over or is not exactly correct, please correct me.

Brief note:  All dialysis patients in USA and Canada (I think) are all on hemodialysis.  The FDA has not cleared hemodiafiltration for use in the USA.  More on this below. I know some centers in Italy, France, and Germany do hemodiafiltration.  In England, dialysis is just too expensive, so your are S.O.L.   (just kidding...)

Hemodialysis:  Uses diffusive clearance....basically osmosis with blood going one way in the kidney and the dialysate (clean fluid...what your blood is "dialyzed against" going the other way...kinda like a countercurrent osmosis system.  The blood and the dialysate NEVER MIX (in theory).  The stuff you want to remove (toxins, potassium, etc), gets out of your blood thru holes in the 'membrane' (the polysulfone, which makes up the hollow fibers in the kidney that is snapped on the front of that dialysis machine.)  The holes are small...too small for cells (like red cells and white cells) and also too small for most proteins to get thru (like albumin). 

Extra water from your blood is removed by the machine "sucking" harder on one side of the kidney (the output of the dialysate side) than the machine is delivering on the input side.  [NOT the blood, but the dialysate...remember there is an 'in' and 'out' port for the blood, and an 'in' and 'out' port for the dialysate on the artifical kidney].  This is called ultrafiltration (...it is an "ultrafiltrate" of your blood...UF for short).  There are very precise pumps for this....called volumetric pumps...that will remove exactly the volume you tell it to.  This is why people don't "crash" on a daily basis anymore....talk to some old-timer nurses, and they can tell stories about the guesswork that used to be involved in setting the UF rate.

OK....so that is the basics.  As I outlined before in the "are you getting enough dialysis" thread, dialysis uses diffusive clearance.  This is good for SMALL molecules (like urea, and electrolytes)...it removes them pretty fast.  However, it is not as good at getting rid of larger stuff (the so called "middle molecules").  These larger things (B2-macroglobulin, B12, etc..) move more slowly via diffusion and it just takes time to remove them.  This is the stuff we don't measure, so the debate is "are we removing enough of this middle molecule stuff?"  There is no known answer to this question (...that we know at this time).
--------------
OK....so how do we make this better.
Rather than using diffusion as the basis of cleaning the blood, we can use hemofiltration. 
Here, there is no dialysate.  The same kidney is used....blood goes in one side and out the other.  But now, we put a cap on the dialysate input side, and just suck fluid off the output side.  This way, we are now using CONVECTIVE clearance.  This uses some fancy physics that I cannot explain, but it is called SOLVENT DRAG...the water molecules that are pulled thru the membrane bring larger molecules with it at a faster rate than by diffusion alone.  This way, we can now remove the bigger "middle molecules" more efficiently than with the dialysis-based DIFFUSIVE clearance.

Now, you may be thinking of a few problems:

1) I will get dry real fast (as we are talking about removing fluid at like 4-6 Liters per hour).  The answer is that we give the fluid back to you on a continuous basis.  And the fluid we give back to you is, basically, the same as the dialysate fluid (Normal sodium, potassium, glucose concentrations, etc..etc..).  So now we call this fluid REPLACEMENT fluid rather than dialysate.  The key difference is that this fluid GOES INTO YOUR BLOOD STREAM DIRECTLY (via the machine, of course), where as dialysis doesn't mix with your blood.

2) What about the smaller molecules that were removed so well with dialysis (like urea)...well, they are not remvoed so well with this techniqe.

3) Is the replacement fluid sterile?:  AHHHH....the key point here.  Lets deal with this below.

4) Isn't this the same effect as the ultrafiltration that is taken off of me every time I go to dialysis?- Yes, it is the same....but no where near the volume is removed on a routine dialysis treatment....lets say 3-4 L is removed on a standard treatment.  A hemofiltration treatment is like 20-40 L removed.  However, you are right, even that small amout with dialysis does contribute to the total clearance that you get with dialysis.   [Side note:- this is my theory on why, some people who are not very compliant with their fluid restriction and get 6-7 liters off a treatment may actualy be getting more "cleaning" as they have more fluid removed via UF....but there is a cost to pay for this, as the cardiovascular system doesn't like these big fluid shifts and this may contribute to heart failure...so they may have better "Kt/V," but have a bad outcome from cardiac disease].


So, as you are probably thinking....if DIALYSIS is good for small molecules, and HEMOFILTRATION is good for bigger molecules.....what happens if we put BOTH TOGETHER!
Then we get HEMODIAFILTRATION.

So, we do the standard dialysis treatment (diffusive clearance), AND we pour in 4- 6 L an hour of replacement fluid into you (and crank up the UF to take that same volume off, so it is neural to the patient, plus the usual additional UF to get you back to your dry wt), and now we just added the convective clearance as well.

The reason this has become possible the past few years is the technology to generate the volume of fluid needed.  120 L an hour is needed for a standard 4 hr dialysis run (at 500 cc / min) and then you need to add to that another 20-40 Liters (or more) of replacement fluid.  Here is the catch....how pure does the replacement fluid have to be?

I can't quote the actual numbers, but the dialysis fluid is NOT STERILE.  It is damm close to it, but not sterile.  The water is purified and usually pushed thru RO (reverse osmosis), and either filtered with 1 micron filters and/or UV light, etc, etc,...such that the final product is really pure.  We use the endotoxin amount (the "dandruff" of harmful bacteria) to quantify just how much is allowed in the final product.  Hemofiltration beggs the question....just how low is low enough?  Since dialysis pts. are exposed of 120 (now close to 200 L with hemodiafiltration) for 3 times a week, 52 weeks a year), a very small percentage of endotoxin exposure can add up.

So, the hemodiafiltration machines actually generate this "extra" replacement fluid from the dialysis fluid from the main center water system...and it is extra-filtered, etc...and is called "ULTRAPURE" fluid.  Is it pure enough?  We do not know yet. 

As I understand it, the FDA is not convinced that this is proven well enough yet, so we can't do this (hemodiafiltration) in the USA.  [If you have been hospitalized and have been on continuous (24hr) type dialysis, you may have been on hemofiltration, but the replacement fluid has to be STERILE fluids....like IV fluid bags they hang at the dialysis unit....you can do this for the slow, continuous type machines, (like 24 L in a day), but imagine hanging 40-60 liter bags per patient, per treatment at the dialysis unit.  Not practical.

Nextstage may do hemofiltration...not sure....but again...has to be STERILE fluid.

What about the downsides to Hemodiafiltration:

1) No outcomes data (some observational stuff...but I am always cautious about these studies...always a "well selected random population..."
2) Bigger stuff gets removed with hemodiafiltration...this may be harmful.  Some albumin and larger protiens get removed.  This can open up a bunch of new problems with ESRD patients.  This may offset any benefits and may be more harmful than before.  Remember, wise men say...."The enemy of good is better..."
3) Cost-  Is all the above worth the extra cost in new machines, more filters, more upkeep costs, etc, etc....
4) Harm of endotoxin exposure (...see above)...
I am sure there are more, but that is a quick list.

Ok....so that is enough for now.
Hope that helps.

I am sure I will get some questions....I am kinda curious myself about this...There is certainly a buzz about this as the technology gets better.  But, newer is not always better.  As with any new medicine or techniqe, I like to move slowly before adopting anything.  This is more so when there is a proven therapy that works (...I know, not perfect...but it works) vs. something new with big promises.  They often don't pan out, or the benefits don't turn out to be that big.
There is ongoing research, so we should find out some more data in the next few years.

[Zach]

Thanks Dr Evil, good info!

Here is a Fresenius 5008 machine that does Hemodiafiltration.

[Rerun]

Interesting.

[kitkatz]

*puts glasses on*  Very interesting.  Thank you for the information Dr. Evil.

[AlasdairUK]

Hi,

I'm in England and my unit uses Fresenius 5008 machines. I'm on Haemodiafiltration.

It is good to know exactly what the difference is, as I was aware of Haemodiafiltration without knowing what the pros and cons are. I'm not sure how many units in the UK use the machines, I was to understand that we are one of the first to use these machines in the UK. I know they do monitor the water on a regular basis.

I have noticed that my phosphate levels are better since a switched to the Fresenius 5008, it may be a better diet rather than the machine. I find it interesting that my unit has adopted this idea which is considered `unproven', but we still do not do the buttonhole technique as the UK does not feel it has enough proof that it is better than the ladder technique.

I quite often come off the machine lower than my target weight.

Please feel free to ask any questions about my dialysis.

Cheers
Alasdair.

[angieskidney]

VERY interesting read! 

[tubes]

I asked my nurses monday about Hemodiafiltration.  Not a ONE knew about it.  I told them to come on here and read the thread.  Doubt anyone did.    

My unit is Fresenius now.  My nurses need to ask about it or something.  I miss RCG. We use to be RCG.  New rules and regulations.  I hate it.  Phew, that feels better.   

[jedimaster]

I am on a Gambro ASK-95 S which is made for home hemo. Yesterday I was reading about a machine that only needs "pipe" and filter changes only once a month....that alone would be an amazing change. My house looks like a warehouse and everyday I have to change tubing, filters, etc.
I also have read about an artificial kidney that uses nanotechnology and goes INSIDE your body....the closest to the real thing....its on trial stage now....and two Companies are fighting for the release of it.

[Zach]

I also have read about an artificial kidney that uses nanotechnology and goes INSIDE your body....the closest to the real thing....its on trial stage now....and two Companies are fighting for the release of it.

http://www.technologyreview.com/read_article.aspx?id=17493&ch=biotech

From the article:
The implant would be tucked under the skin; small fluid bags worn externally could receive the ultrafiltrate and supply replacement electrolytes.

A more sophisticated form of PD.  No thank you.

[angieskidney]

From the article:
The implant would be tucked under the skin; small fluid bags worn externally could receive the ultrafiltrate and supply replacement electrolytes.

A more sophisticated form of PD.  No thank you.

Ya that is what that sounds like ....

[jedimaster]

What I was talking about is this:
"Rosengart and codeveloper Michael Kaminski, an engineer at Argonne National Laboratory, have developed a fast and simple solution using magnetized nanoparticles attached to receptors designed to identify and grab target toxin molecules. The nanoparticles are injected into the bloodstream, where they circulate through the body, picking up the target toxins. To remove the particles from the body after treatment, a small shunt inserted into an arm or leg artery quickly routes the blood through a handheld unit with a magnet. Since the nanoparticles are made of polylactic acid, which is biodegradable, any remaining particles will eventually be eliminated from the blood. So far, tests have been limited to rats, but the results have been promising. "Our initial tests have been very successful -- I am very confident that we will be able to remove 99 point something of the particles," says Kaminski. Once perfected, this type of approach need not be limited to patients with renal failure but can be used to augment everyone's detoxification capacities.

An even more advanced machine being developed for cleaning the blood is the bioartificial kidney, which uses a plastic cartridge containing a billion human kidney cells inside of 4,000 hollow plastic fibers. It is being developed at Nephros Therapeutics, based on research by University of Michigan internist David Humes. It will deliver the full range of kidney functions, including its immune-system-regulating activities. In a partial clinical trial, 6 out of 10 critically ill patients survived; all but one had been judged to have no more than a 10 percent to 20 percent chance of living. This combination biological/artificial kidney could be available for widespread use by 2006. "

Sounds better (to me) than been attached to the machine 5 days a week....what do you think?

[Rerun]

Here is a link to Dr. Humes study.

http://www.med.umich.edu/intmed/humes/

[Zach]

We should get back on topic.

But here are the threads about Medical Breakthroughs:
http://ihatedialysis.com/forum/index.php?board=8.0

[AlasdairUK]

What about the downsides to Hemodiafiltration:

1) No outcomes data (some observational stuff...but I am always cautious about these studies...always a "well selected random population..."
2) Bigger stuff gets removed with hemodiafiltration...this may be harmful.  Some albumin and larger protiens get removed.  This can open up a bunch of new problems with ESRD patients.  This may offset any benefits and may be more harmful than before.  Remember, wise men say...."The enemy of good is better..."
3) Cost-  Is all the above worth the extra cost in new machines, more filters, more upkeep costs, etc, etc....
4) Harm of endotoxin exposure (...see above)...

My view on hemodiafiltration is very positive and would recommend it to anyone who has the chance to use. I'm currently on post hemodiafiltration as opposed to pre hemodiafiltration. My response to four downsides of hemodiafiltration:

1)  More and more data is being collected every day.
2) Monthly checks on your Albumin levels to make sure they are adequate. Bare in mind all dialysis patients need to keep their protein levels up not just hemodiafiltration patients. This concern is for everyone.
3) New machines need to be purchased over time and phased in to replace older models. When this happens you can include hemodiafiltration machines. Cost will always be a factor with dialysis machines. The newer machines are more effective and cheaper to run.
4) The replacement fluid is very pure with regular checks. There is always some degree of risk with dialysis. I feel the benefits outweigh the risk.

I would be interested to know the view of anyone else on hemodiafiltration. I am reluctant to travel to any centre that does not use hemodiafiltration as I do not think the treatment is as good.

[Zach]

 

[mamanan62]

What I was talking about is this:
"Rosengart and codeveloper Michael Kaminski, an engineer at Argonne National Laboratory, have developed a fast and simple solution using magnetized nanoparticles attached to receptors designed to identify and grab target toxin molecules. The nanoparticles are injected into the bloodstream, where they circulate through the body, picking up the target toxins. To remove the particles from the body after treatment, a small shunt inserted into an arm or leg artery quickly routes the blood through a handheld unit with a magnet. Since the nanoparticles are made of polylactic acid, which is biodegradable, any remaining particles will eventually be eliminated from the blood. So far, tests have been limited to rats, but the results have been promising. "Our initial tests have been very successful -- I am very confident that we will be able to remove 99 point something of the particles," says Kaminski. Once perfected, this type of approach need not be limited to patients with renal failure but can be used to augment everyone's detoxification capacities.

An even more advanced machine being developed for cleaning the blood is the bioartificial kidney, which uses a plastic cartridge containing a billion human kidney cells inside of 4,000 hollow plastic fibers. It is being developed at Nephros Therapeutics, based on research by University of Michigan internist David Humes. It will deliver the full range of kidney functions, including its immune-system-regulating activities. In a partial clinical trial, 6 out of 10 critically ill patients survived; all but one had been judged to have no more than a 10 percent to 20 percent chance of living. This combination biological/artificial kidney could be available for widespread use by 2006. "

Sounds better (to me) than been attached to the machine 5 days a week....what do you think?









EDITED:Fixed quote tag error-kitkatz,Moderator

[aharris2]

Interesting "bump" Zach. It is now 3 1/2 years later. AlasdairUK uses (used) it and is (was) a proponent.

4 to 6 liters per hour, 16 to 24 liters for a 4 hr treatment...

The average dialysis treatment moves, what, 3 liters of fluid and the techs don't handle that well. I find the amount of fluid in hemodiafiltration scary. How quickly can a patient be killed by incompetence at that rate of fluid movement? What are the safeguards?

[billmoria]

Hi Greg and thanks. Every day dialysis lets me stay with the person I love is a bonus. I don't feel great every day physically but I am so happy to spend another day.

I have never suffered low BP on the 5008. Twice in 4 years doing HD on another machine. It is not unknown in our unit but on the 5008 I have had great luck - long may it continue.

I have had dialysis on holiday in the states. My last trip to Florida at a DaVita clinic. I was sick after each and every session. I better results at a Fresenius clinic in Connecticut.

You did a good job on the 3D rendering - keep up the good work

Cheers Bill

[Bruno]

I don't know about the 5008, but I agree with Bill, new machines will happen. I know water quality is important...my 4008 has 3 filters attached to it and Frensenius just put a fourth one on the back of the machine, called Dialsafe. It adds 4 minutes to the test.

[Des]

HDF - I am currently doing HDF and just want to let you know....

It not only removes large molecules but mid and small as well. (HD goes for the bigger ones only.)

This has a VERY positive effect on the longterm outcome of dialysis pasients as  no build-up of toxins take place.

The down-side might me that it cannof diffirentiate between good and bad and you sometimes need to put the good ones back (vitamins) but all in all it is a fabulous new way of getting rid of the toxins.

This is by no means medical terms but it is how I understood it.

       

[Stoday]

we still do not do the buttonhole technique as the UK does not feel it has enough proof that it is better than the ladder technique.

That's not true. My unit in the East of England encourages the use of buttonholes. Only the newbies use the ladder.

[billmoria]

I know you were kidding but dialysis is free on the National Health Service. The NHS gets a bad press in US.

I use the F 5008 and have been for 2 years. It does a better job for me than the other machines in our unit. I am at Queens Hospital in the UK and I am on the button hole technique which all clinics under the Royal London/Barts Hospitals offer. I love the blunt needles - it never hurts and my bleeding at the end is not just 4 minutes per hole.

I feel better the next day - most of the time - as compared to HD. Not every oneinn our unit is on button hole and not everyone on button hole uses the 5008. they just try to find what works best for different people.

Bill

[KICKSTART]

ALL the machines on our unit are 5008 and everyone does HDF ..everyone except me ! If people that dont know me would care to read my previous posts , you will see just how much trouble i have had on HDF. Ive had everything blamed for the cause except dialysis itself ! My problem WAS HDF and thanks to one nurse who suggested i try HD im now better than ive ever been ! I am not saying it wont suit everyone but I certainly wouldnt recommend it ! It made my life a misery to the point of thinking of giving up !

[Bruno]

Bill, my main questions would be...are you getting better outcomes ie clearances etc and are your session times any shorter? It seems to me that the machine must offer something better than previous models, otherwise what would be the point?
Also, I'm fascinated by your reference to 4 minute pressures...I presume that to mean that it only takes 4 minutes to stop the bleeding when you pull the needles out at the end of a session. I have been told to take 10 minutes at least.

[KICKSTART]

Bruno i did nothing but suffer on HDF.  My clearances are better on HD but only because i can do the full 4 hours , on HDF they had to take me off after 3 i was in such a state, and NO the session times on HDF are not any shorter !