Technology: What Is



The NxStage system


·         NxStage was approved (FDA) for home HD … June 2005 

·         Approaching 5,000,000 treatments have now been performed, at home, in the US

·         Over 5000 patients are now using NxStage in US

·         It can be fairly said that the NxStage system has been solely responsible for the upsurge in HHD interest in the US  

·         The NxStage ‘off-shored’ the US in 2009 and is currently being evaluated by, or is already being used in …

        the UK, Ireland, Sweden, Denmark, Norway, Finland, Netherlands, Belgium, Australia, New Zealand, France, Italy, Turkey and some Middle East countries



The NxStage system provides either a ...

·         a single pass lactate dialysis fluid, via a ‘batched’, Pureflow™ -generated dialysis fluid (using 20 to 60 litres/treatment) ... depending on the treatment duration

or  …

·         ... a sterile, bagged 5L dialysis fluid (using up to 5-6 bags/treatment)

·         Both … the Pureflow™ and the bagged dialysate … provide an ultrapure dialysis fluid

·         Dialysis fluid flow = 100 to 200ml/minute (mostly around 100 ml/min)

·         Blood flow = 300 to 600 ml/min

·         It is promoted as a ‘portable’ dialysis system

o   the machine weighs 32 kg

o   the bagged dialysate weighs ~30kg/treatment

o   the PureFlow™ dialysate generator is not portable

This, in my view, means the system is not really ‘portable’ ... at least not for ‘average Joe’ ... but, rather, is ‘transportable’

·         The NxStage disposable cartridge includes:

o   a single-surface-area-choice HFAK artificial kidney, dialysate and blood lines, and a medication port

o   there is no air-blood interface ... allowing a lesser heparin dose

o   it is a ‘wipe-down’ disinfect system

o   there is an automated prime and rinse back process


·         The Pureflow™ system provides near ultra-pure water to generate its’ 60L batch of dialysate

·         Its’ potential home modalities include:

o   Short daily (5+ treatments/week)

o   Every other day nocturnal treatments

o   Daily nocturnal treatments (5+ treatments/week)


Understanding the NxStage ‘Flow Fraction’

One thing to get one’s head around is the way the NxStage system reverses the usual relationship between the blood and dialysate interface

‘Normal’ single pass systems run a very high dialysate flow rate (Qd), commonly 500 or 600ml/minute, past the dialyser membrane while the blood flow rate (Qb) is much slower (between 250 and 400 ml/min). In single pass systems – the usual dialysis machines we currently use – the blood flow rate is roughly half, or a little more, of the dialysate flow rate.

The NxStage reverses this flow relationship between Qd and Qb …


        Conventional HD  = high Qd (600) and low Qb (300) = 2 x

        NxStage HD           = low Qd (100) and high Qb (300) = 1/3rd x


·         Understanding this ‘reversal’ is the key to understanding that this machine treats HD rather like PD

·         It ‘operates’ at dialysate/blood saturation and equilibration ranges that are more like PD than HD

·         The Qd/Qb ratio in conventional HD usually approaches 2

·         The ratio (filtration fraction) in NxStage Rx = 0.3 - 0.5


... but … the NxStage is really no longer ‘new’ technology ... in truth, it is now getting to be old(ish) technology 

One thing that can never be taken away from NxStage though – whatever the future holds for it and the other emerging systems – NxStage has been solely responsible for the resurgence of interest in home dialysis in the US ... and interest that took far to long to take root.

So ... well done, NxStage. You have served dialysis well.




Authored by Prof John Agar. Copyright © 2012
Nocturnal Haemodialysis Program, Barwon Health.
All rights reserved. Revised: July 1st 2012