Aksys announced in mid-January that they’d be declaring bankruptcy this month, all PHDs had to be pulled from service by January 31. They came for my PHD on Tuesday 1/30; my last PHD run was Monday night. I think I started using the PHD August 22, 2002 so I had a 4 year and 5 month stretch receiving I think the best dialysis minute for minute that I’ve had in 16+ years as a dialyzor.
As far as my impressions I’ll put aside the obvious - portability, support model (NxStage) biocompatibility, F80 kidney (Aksys) and most importantly the System One is available, the PHD is not - and talk about the central question: dialysate flow rates (Qd). The NxStage System One turns conventional wisdom on its head; I am trying to understand, trying to revisit my assumptions and identify any baseless biases, as always I reserve the right to be wrong and change my mind. I offer my impression as an individual who has experienced a wide range of hemodialysis modalities and as one who tries to understand the choices we dialyzors face and also understand the choices faced by the dialysis manufacturers and providers. So while I write of the differences between the PHD and System One, really it’s their approach to the choices that resulted in two very different machines, it’s that approach that I’m comparing.
Dialysate is at the center of this, a limited quantity of dialysate is what both machines have in common and how they employ this limited quantity of dialysate is what differentiates them. Some background: both machines use ultrapure dialysate which apparently can not be delivered on demand. Dialysate is delivered on demand by a standard dialysate delivery system. While a standard home dialysate delivery system (RO, carbon tanks, acid & bicarb jugs) meets all current purity standards, ultrapure dialysate has shown clnical benefits so both companies made the choice to use ultrapure dialysate. The PHD makes 50 L of ultrapure dialysate each night, and uses 50 L each treatment. The System One with the PureFlow makes 60 L of dialysate at a time and uses 20 to 60 L each treatment (there are bags but day to day I’m using the PureFlow).
The PHD squeezes the maximum dialysis value out each unit of dialysate by multi-passing i.e. running its 50 L of dialysate through the artificial kidney about once every 62 minutes (Qd=800). There are studies that show the advantage of Qd twice blood flow (Qb). My understanding (as a journeyman in the Carpenters Union) is that in an artificial kidney when blood & dialysate are traveling in opposition on either side the permeable membrane at this ratio: Qd >= 2 x Qb, a sort of “molecular magic” happens along the membrane – shear. This shear makes solute transport more efficient – more dialysis. The PHD also increased solute transport by artificially increasing the UFR by .8 L/hour which triggered convection when the gross UFR was greater than 1 L/hour.
The System One squeezes the maximum dialysis value out each unit of dialysate by slowing down i.e. running its 20 to 60 L at Qd less than Qb. The System One is new; I haven’t seen peer reviewed data on this approach but I can repeat what I’ve heard. The System One works by increasing the “dwell time”. By using slow dialysate speeds the dialysate spends more time along the membrane saturating it so that a different “molecular magic” happens – call it saturation transport. Ones peritoneal dialysis dose is a function of dialysate quantity and dwell time, the System One uses the same language. The idea is that by slowing the dialysate down – slower is better – the dialysate has more time for solute transport.
The System One does work. However, against the proven efficacy of the F80 combined with Qd = 2 x Qb it is not clear if I am gaining anything clinically for the extra time I am compelled to invest. So I guess there are two questions: am I getting the most out of my time on the System One (less dialysate/lower FF or slower Qb/higher FF)? And how much time (dialysate) do I need to use? It would be nice to get back to a 170 minute run which was my PHD standard but that is not the main goal. I understand the many ways to shorten ones treatment time on the System One but they all involve subtle changes to dose. What I want to know is what I would have to do at a minimum to have as good a clinical outcome on the System One as I experienced on the PHD. To state that more generally: what is the System One equivalent to a Hemodialysis Product (HDP)= 100?
A HDP = 100 on the PHD required about 3.5 hours a day gross (treatment time + pre + post). My current System One regime is taking five + hours gross, HDP unknown. Looking ahead I think I’ll try to multi-task the treatments by either working (telecommute, doing CAD for a company that sets up conventions and trade shows) or sleeping i.e. nocturnal or some combination. The lifestyle goal is to get to bed after walking the dog before 11 PM (ideally 10 and read in bed) and up at 6:30 AM well rested and well dialyzed. I’ll get there.