Water requirements for NHHD?

Hello Dr John,
Have been following your web site for a few years now, though I am not on dialysis yet but very close. eGFR 11.
Water is a big issue where I live. So I was wondering if you can tell me what blood flow rate is typically used for a Night Home Hemodialysis of 7-8 hrs/night for 5 nights /week, and therefore what might therefore be the typical dialysate flow rate for this blood flow. I have read somewhere that dialysate flow rate needs too be 1.5 times blood flow rate at least. Is this correct?
It has also been indicated to me that NHHD requires far smaller blood flow rates than the usual 500ml/min and, I am hoping, a smaller water flow rate as well.
Look forward to your reply,
Paul Cruice

Dear Paul
Sorry I have missed this question for so long - for some reason the messaging system no longer alerts me to the posting of new questions or comments. I will respond later today with some answers to your question(s).

Dear Paul

Firstly, it is good to see that – faced with a bad hand – you are doing all you can to find out about dialysis before you need to start. So many do not do this, and struggle to catch up once faced with the actuality of dialysis. So … well done.

Water is a real issue in this dry land of ours – especially now in non-metro regions of Queensland and NSW where drought is ever a threat and a current stark reality and we need to be smart about its use – especially in dialysis where the need for ultra-pure water – and lots of it – is a fact of life.

As you will be aware, there are two main types (we call them ‘modalities’) of dialysis: haemodialysis and peritoneal dialysis. As you have only referred to the data applicable to haemodialysis, I am presuming your choice has already been made between the two options, and that you have discussed both with your treatment team. Peritoneal dialysis requires no significant water use in the home – though significant water is used by the manufacturer in the preparation of the dialysis fluid that is pre-prepared and delivered to your home: this, of course, is not of direct concern to you, nor a drain on your local water services. However, it must be said that peritoneal dialysis is the most water-sparing dialysis option for people who live in water-scarce regions, yet who want home dialysis.

As you have focused on home haemodialysis, this is where I will concentrate the rest of my remarks.

When it comes to home haemodialysis, there are two major dialysis machine options. In Australia, we believe that optimal dialysis is best provided by using single pass dialysis systems: typically the Fresenius or Baxter/Gambro machines that I am sure you are familiar with. In the United States, home dialysis is more commonly provided using the low-flow NxStage system – a system that certainly does draw less water. However, as I have written much about elsewhere, there are reasons why in ANZ we have a preference for the more water-hungry but more optimally dialysing systems: Fresenius and Baxter/Gambro. While these systems do use more water, they offer greater flexibility in time and frequency – especially for patients wishing to dialyse frequently and for long hours at home – while they also allow ‘deeper cleaning’ and better clearance profiles. With the exception of a small pocket of NxStage use still clinging on in FNQ, the rest of Queensland, Australia and New Zealand use single-pass systems.

That said, I will restrict all further remarks to single pass dialysis – far and away the more likely option that will be being considered for you as a home dialysis platform.

In conventional satellite or in centre haemodialysis management, there is an old rule of thumb that says that the dialysate flow rate should be between 1.5 and 2 times the blood flow rate. As most Australian and New Zealand services use blood flow rates of between 275 and 325 ML per minute with very few using blood flow rates in excess of 350 ML per minute, this means that most dialysate flow rates are in the range of 500 to 600 ML per minute.

Again focusing on the single pass dialysis systems that we use in ANZ and coming back to that ratio – where the dialysate flow rate is ideally set at somewhere between 1.5 – 2 x the blood flow rate – in very simplistic terms, if the dialysate flow rate is set at, say, 500 ML per minute, a primary water draw three times that amount (i.e. about 1,500 ML per minute = 1.5 L per minute) would be required

If you then do some simple mathematics, to run a machine for, say, 4 hours, a water draw from the primary source of 1.5 x 60 x 4 L per dialysis session = 360 L would be needed to provide 0.5 x 60 x 4 L of RO filtered water for the dialysis session. In dialysis units, where machine prime, in-between-dialysis-sessions idle, and rinse phases are common, almost 500 L are actually (wastefully) consumed by each patient, for each dialysis session, three times each week, ad infinitum!

At home, dialysis machines typically draw their water from the reticulated town mains water supply or, in rural or remote regions, sometimes tank, rain, or bore water where ‘town water’ is unavailable. As any water drawn from any/all of these sources to create dialysate must first be particulate filtered, carbon filtered, softened (where/when needed), then subjected to reverse osmosis filtration – at home using small, individual, stand-alone RO systems that are typically a little inefficient – the volume of water drawn from the primary source needs to be about three times the volume that will ultimately be used to create the dialysate. This is because individual, single person RO machines commonly ‘reject’ around two thirds of the water drawn from the primary water source and pass only about one third through the RO membranes for the machine to form the dialysate.

In Australia and New Zealand, home dialysis is commonly encouraged to be more frequent than three times a week with a wide range of sessions per week from alternate day or night through to 5 or 6 day or night sessions per week (we favour 7-9 hours [mean 8 hours] x 4-5 sessions each week).

But … because dialysis sessions at home are typically more frequent and go for much longer (ideally over-night and while asleep = so-called nocturnal haemodialysis = my preferred model), many of the ‘levers’ that we use to achieve optimal dialysis can be dialled back.

The blood flow rate does not need to be as high as it is for in-centre care [ typically we run home dialysis blood flow rates at around 225 ML per minute ] while the dialysate flow rates can also be reduced [ typically we use a dialysate flow rate of 300 ML per minute – though some units do set their home systems to 500 ML pre minute ].

Even at this much lower home-specific dialysate flow rate, water use will still be profound. Again, doing some simple maths, if 300 ML per minute is maintained as the dialysate flow rate, then a 900 ML draw from the primary water source would still be required to allow one third of the mains water draw to pass through the RO for dialysate use with the RO still ‘rejecting’ two thirds (600 ML per minute). For an eight-hour treatment, mains water (or bore water or tank draw) would be 900 x 60 x 8 ML per treatment … or, in litres, this would be 0.9 x 60 x 8 = 430 L per treatment. Add in run up and rinse use this, and again, it approximates 500 L of mains/tank/bore water per treatment.

Paul … based on (1) chosen hours and frequency and (2) knowing the ‘reject rate’ of the RO – your team could give you an estimate of this but most individual RO’s have a ‘reject’ rate of about 2/3rd rejected to 1/3rd through to the machine – you can do your own back of the envelope calculation of the likely water draw and, knowing the cost per KL of water in your area, a calculation of cost can be done. In Australia, all states now reimburse home patients for their utilities cost (or at least a proportion of it) although some states are more ‘generous’ (e.g. Victoria) than others. Your local service should help you to access the pro rata reimbursement scheme extant in your state once you start out on home dialysis.

To get around this profligate water use, we introduced a number of water-saving options about 15 years ago. These are described in a paper we published in 2009 in Hemodialysis International: Agar JWM, Simmonds RE, Knight R. Using water wisely: New, essential and affordable water conservation practices for both facility and home hemodialysis. Hemodialysis International 13(1):32-37, January 2009. We have written many other (20+) journal-published papers on this topic but the paper I quote here – our first such – has most of the simple details, despite that we have refined many of our options since.

In brief, this paper details a series of both re-use options for RO reject water and/or RO reject water re-circulation techniques. Both or either yield marked water-sparing. These options could/should be discussed with your service. What can be and/or is provided will depend on their capabilities.

Finally, I think you may have ‘confused’ blood flow rate and dialysate flow rate in the last question of your post … “it has also been indicated to me that NHHD requires far smaller blood flow rates than the usual 500ml/min and, I am hoping, a smaller water flow rate as well” … but I hope my answer will have sorted this out for you already.

Hello Dr John,
Thank you very much for your very thorough reply to my inquiry. You have given me ALL the information I needed.
As part of my quest to know as much as possible about what I am yet to experience, I do research such things as other machines in the world e.g. Quanta SC+ and more recently a much more efficient RO system found at this url (https://www.desalitech.com). They are talking about 92-98% efficiency instead of the usual 50-60%. I am also looking into ways of generating water from humid air much as WaterGen Gen-350 does in the USA but the cost of it here is way too high yet. It produces about 900 litres/day of clean drinking water.
Well, once again thank you for your excellent reply. I do hope the Christmas period is kind to you and family and I wish you all the very best for 2020.
Paul Cruice