Concerns with the NxStage System One?

Hi Dr. Agar,

I have continuously marvelled at the freedom the NxStage System One has given to people on dialysis in the US. The things that they are now able to do compared to those who do not have a portable machine or worse - are in centre. I have often felt sad that I do not have access to this wonderful machine in India because of which, though I dialyse at home, I am unable to travel with ease. My trips are restricted to short 1 or 2 days or to places that have centres where - and I absolutely abhor this part - I have to go in centre to dialyse.

I read your concerns about the NxStage on an Facebook post recently where you mentioned that is it not good for the fistula. I went back today trying to look for it as I wanted to understand it better. However, I could not find it. I was wondering if you could please let me know what the concerns are with using the NxStage. I am trying to get the NxStage machine to India and it would help me greatly if I knew the concerns you had with this machine.

Thanks so much!


Dear Kamal

I feel that I seem to have discussed this, answered this, many times.

It was recently, I think, a topic on the Facebook site and in discussion with Peter Laird and others.

Before I type it all out, yet again, I will email Peter and see if he has the thread still available - or can find it - as I no longer subscribe there and cannot search it for you. Alternatively, perhaps Dori can find the discussion there and copy it here.

I think this was the part you were looking for, Kamal,

" I know some of you will have picked up that I am not fully convinced about the NxStage system. Why? Why has there been a reluctance in my part of the world (all the ‘error’ issues alluded to by Maz and Trevor aside) to accept this nice little portable machine? Well, the NxStage was designed (primarily) for US dialysis, for a home HD market that it (the NxStage) has almost on its own - and spectacularly - grown from nothing to a now creditable 1-1.5% of dialysis. Full marks and all credit to it that it has done so! But, it was designed principally to provide fast, hard (bad) but more frequent (good) dialysis, but in the home. To do this, but with a limited volume of bagged or batched dialysis fluid - ultra pure, as Peter rightly says … a clear tick - it had to introduce a reversal of the standard dialysis practice of a high dialysis fluid and low blood flow ratio. It had to turn that long-standing dialysis dictum around and on its head, instead scripting a high blood flow to low dialysis fluid flow ratio - a reversal it named as the filtration fraction. In ‘conventional single pass’ dialysis (ie: Ian Chitty’s Fresenius 4008B which, incidentally, we also use here in Geelong) - or any similar single pass system - the blood flow rate is commonly about half the dialysis fluid flow rate … say, a Qb of 250 -300 ml/min paired with a Qd of 500-600 ml/ min. But, NxStage was (at least initially) limited to a 25-30 litre dialysis fluid batch. While it can do a bit better than that now with the PureFlow, it can still, at best, only offer a maximum dialysate volume per treatment of <60 litres. To compensate for this very low dialysis fluid volume and its associated low Qd, the counter-current pass of blood across the dialyser HAD to be ramped up! That meant reversing the Qb:Qd ratio so that Qb was 2-3 x greater than Qd … the very opposite of conventional dialysis where Qb is only 1/2 the rate of Qd.
The problem, for us here in ANZ, is that we think this only serves to rob Peter (pun intended) to pay Paul!
To get anywhere near adequate clearance, the NxStage system and its blood/fluid flow dynamics required a very high Qb … in turn demanding that the AVF be driven at flows that were anathema to us … and, to be honest, they still are. We do not use high a high Qb. We think high Qb’s are detrimental to good AVF care. Using the kind of Qb needed to compensate for the low flow dialysis fluid rates of the NxStage simply, to our view, introduces another ‘bad’ thing into the dialysis equation. Not only is a venous ‘blast’ back into the return vein of 350+ anathema to us, but to run a Qb of 350+, an arterial end ‘suck’ of the same amount is needed … with the potential (and actual) result of structural damage to the AVF the arterial end too - at BOTH ends - venous and arterial. To be plain, we don’t think that’s a good trade, if you dont have to. And, in single pass systems, you dont have to!. But, turning down the pump speed on a NxStage to 300-ish (or, better, even lower - NB: our home patients on single pass systems run Qb’s of 225 ml/min) would cause the filtration fraction physiology of NxStage to fail, and ‘adequate’ dialysis clearance would be unachievable.
So, for this, and other reasons, we have decided to stick with what we do … at least until newer, portables appear that allow low Qb’s yet provide for a high clearance by still allowing a high Qd. How might that happen. Well, sorbent regeneration of the dialysis fluid for reprocessing then re-passing the dialysis fluid around and around, would allow that … but, we would have to be convinced of (a) safety and (b) that the sorbent would not be supersaturated such that breakthrough occurred. It’s not a new concept … some of the ‘old hands’ like Nancy,will recall the REDY system. Other options may also emerge, but that discussion is not for here or for now.
Meantime, we remain comfortable, here in ANZ, with providing good dialysis clearances yet at low pump speeds (low Qb’s) … and we are likely to continue to do so until something better is on offer. Dialysis is, in essence, a trade off - as no system is ideal - but we believe it best to recommend to our patients to trade what is, in truth, still difficult portability for better fistula care, optimal small and middle molecular clearance and, through longer dialysis, to ensure a low UFR that does not threaten myocardial stun and allows intra-dialytic trans-compartmental fluid equilibration. For the reasons that underpin this last point, see the HDC blog on the Dialysis Waterfall Part 1. I think that will be our collective view here, at least till something better comes along.
Dori is right, choice IS important, and while mobility DOES matter to many, it is important, too, to make sure that patients who choose mobility understand that by doing so, they may sacrifice other benefits.
Now … I can just imagine a raft of posts coming back in response to this post … “I have run at flow rates of 450 for decades and my AVF is fine - etc etc” … and that may well be true, for some - but it is unlikely to be true for most or all.
Again, the weakest link in your life-sustaining dialysis is not the machine but your access. Access protection HAS to be a paramount priority. I try to live and deliver that priority."

Thanks Dori, that WAS the one.

This post originally appeared in the more ‘modern’ Facebook version of the HDC Message Boards, and there are a couple of references within it to ‘Ian’ and Peter’ who had posted prior comments, to which I was responding. These, and a couple of unfixable typos aside (I can’t re-edit the answer I gave (above) that Dori has very kindly copied in for you) - and the post still stands, as I think it should.

In essence, the NxStage is a nice machine. It does offer portability - though that portability is still not simple and easy for many - and it is undeniable that the NxStage ans its (now three) delivery systems has transformed home care in the US.

But, any machine can do home dialysis. Any. Home care is not machine-specific (as you, in India, and we, in ANZ, well know). However, as a result of a great little machine and some very smart and largely unopposed marketting, many in the US seem to almost equate home dialysis with one single machine option - the NxStage - and, to be fair, this is not the case. There are sacrifices … especially to optimum middle molecular clearance and also, potentially, to fistula integrity … that I believe that a person who uses the NxStage must accept as the ‘down-sides’ of its use. To be equally fair, there are just as key a set of down-sides to the use of single pass systems like the Gambro or Fresenius systems - lack of mobility/portability and, as you rightly point out, the difficulty of holidays … and to some users, these deficits may well outweigh the NxStage deficiencies.

Fair enough, I say, fair enough. But, no system delivers all optimums. Not one. What you gain from some, you lose with others. That’s my point. My whole point. Know what you gain - yes - but also understand what you might lose … then make your decision about what is important to you.

Here in Australia, broadly - but not exclusively - most services have chosen to stay as we are and have been … for the main part, for the reasons I have given. But, I believe, we would also be very unwise to exclude the NxStage here, as some may make the choice for mobility (like Trevor and Maz … the original ‘posters’ of the thread at the Facebook site I commented on … who were Australian, and who were strongly supporting the mobility aspect of their NxStage system).

I think all systems have their place, have their strengths, and have their weaknesses, and all should be ‘available’, I simple seek to ensure that all home patients understand - and should be educated to understand - that no one machine does it all.

If mobility is your absolute ‘key’ requirement … fine. But, understand what you may lose.

If optimum dialysis and fistula longevity is your absolute ‘key’ must-have … also, fine. But, understand what you may lose.

Sadly, at least at the moment, I fear no system caters yet for the extremes on both sides of the coin.

While we ought, as providers of your care and as a profession, should be in a position to offer all choices, we, too, are entitled to have opinions, biases, and beliefs. And, these opinions, biases and beliefs should and do carry weight with, and influence the direction that home care has taken in different parts of this weird and variable world we live in.

It is the interface between all these sometimes competing variables that we must manage and negotiate, as best we can, till even greater choices unfold, choices that will hopefully solve some of the current apparent impasses that like me prattle on about.

Thanks Dori for finding that and posting it!

I agree with you Dr. Agar that each patient must make an informed choice keeping in mind the advantages and disadvantages of each option.

How nice it would be if we could use the traditional machines for the most part when we’re dialysing at home and our clinics had a few NxStage machines available whenever anyone wanted to travel!