That is a very good question! I have to say we use high flux membranes here for all dialysis – and that is pretty much the norm, Australia-wide. Further, that applies, not just to nocturnal patients, but across the board for all dialysis … facility and home … conventional and otherwise. Reuse was outlawed in about 1993 and most Australian units have been on high flux dialysers for at least the last 5-8 years. So, I guess, high flux is just what we do!
Of course, high flux dialysers are also ‘leakier’ … and that goes both ways across the membrane so that not only can more solutes ‘get out’ but, potentially, more water-borne ‘nasties’ … eg: endotoxins … get in! as a result, we believe that the use of high flux dialysers demands the additional use of an extra in-line water protection device. We use a Diasafe, changed each 3 months, between the R/O and the machine. The use of the Diasafe adds a significant cost of about $A160/home patient/each 3 months … but we believe they are a non-negotiable accompaniment to the use of a high flux dialyser.
As for whether a high flux membrane is necessary in longer, slower, more frequent dialysis … and I note that you do 7 hours x 6/week (and that is 42 very good and highly beneficial hours too, I might say) … is clearly debatable.
There is a little evidence, we think, that the clearance of B2 and homocysteine do improve with high flux membranes. We measure these routinely in all patients each 6 months … along with a range of measures of inflammation like CRP and ferritin every 3 months. One of our Registrars or, in the US, that would read ‘one of our Fellows’ presented our data on this some years back at the ANZSN … see our nocturnal-related publication list at my website for this.
The clearance of B2 and homocysteine (and presumably other) so-called ‘middle molecules is already markedly better in low-flux but high-hour, high frequency dialysis when compared to low-flux conventional 4-4.5 hour 3/week dialysis so … how much extra benefit accrues?
I have to say that I don’t know, as I am unaware of any head to head studies other than our small crossover series that looks at this issue and there is certainly no outcome data available in this area. I hear some groaning ‘why don’t you know’? … my answer? … well, we can only do so much! … and I know that is not a good answer but it is the practical one!
Cost matters! … for us, as it also does for you. The early data from Andreas Pierratos on the clearance of B2 was, as I recall without looking it up, all with low-flux kidneys and dialysate flow rates at 100ml/min. The increase in B2 clearance was (even then) highly significant. And, as you say, the removal of phosphate is so good as to require its replacement in many of the 25-30+ hour/week patients … and yes, this will be further magnified by a high-flux membrane.
However, there are still no documented dialysis-induced deficiency syndromes (apart from phosphate) from ‘over-dialysis’ that I am aware of.
I hope that has helped make things a little clearer … though reading back, I am not so sure! If you can’t easily afford high flux membranes … and the extra addition (and cost) of the Diasafes (4/year) that those high flux membranes would require … then I doubt you would be too disadvantaged with the low-flux alternative. My view? … high flux + Diasafe = best. However, low-flux extended hour dialysis – especially ot to the 40hr/week+ that you are getting – is still far superior to conventional 12-15 hour facility-based dialysis, even if that is high-flux based.