There is no reason why you can’t do single needle SDHD x 6/wk x 2.5 hrs/session via single needle access (I’ll abbreviate this now to SNA), as long as you understand a few basic things about SNA.
- Noise
First, we tried SNA some time ago using a flow-reversal system … several of our patients tried SNA in nocturnal dialysis for us some 12 years ago though this was within a 6 night/week x 8-9hr/session program. The reason we gave it away was simply because the flow reversal click-clack of the double pump system was too noisy for our patients to sleep.
Noise can be an issue – though the machines are better and quieter now and the Gambro AK200s shouldn’t be too bad in this regard. In addition, as your wife is doing SDHD and is therefore not trying to sleep during dialysis, this issue will not have the same impact for her as it did for our patients who were trying to get to sleep.
The double pump system is quieter, but in most machines there is still a bit more ‘squishing’ happening.
- Dead-space
One potential issue with SNA is that there is always going to be a small amount of what is called ‘dead-space’ at the end of the needle … what I mean by this is that a small volume of the ‘already dialysed blood’ that is being returned back to the patient from the dialyser during the ‘push’ (or venous return) cycle will be the first few mls of the ‘draw’ (or arterial delivery) cycle of the next machine draw. This will marginally – but only marginally – reduce the efficiency of the dialysis process by what is called ‘in the trade’, recirculation.
To be honest, I think more fuss is made about this than is either needed or warranted, and I would not take too much notice of it. In any dialysis treatment, the most efficient removal of most small solutes (wastes) is when their concentration in the blood is the greatest and thus the ‘gradient’ between the blood concentration and the dialysis fluid concentration is at its greatest … ie: at the beginning of the treatment. SDHD uses this ‘efficiency advantage’ to the maximum and thus any small reduction in efficiency through recirculation will exert a minimum impact on the efficiency of the dialysis as a whole.
- Flow rates
Because SNA dialysis with a single pumps system involves flow reversal – first draw, then push – it is preferable that the blood flow rate be increased to compensate for this and she would probably need at least a 250ml/min+ blood flow rate to get adequate clearances. This can be monitored initially by pre and post bloods, drawn to assess solute clearance but, on a 6 day x 2.5 hr treatment, it would surprise me if her small solute clearances were not adequate.
- Phosphate
One unknown would be phosphate clearance. Phosphate, while seemingly a small solute, behaves more like a middle molecule with its clearance being determined, not by gradient, but by dialysis time. Again, this would need to be watched by blood tests to ensure sufficient phosphate clearance if using a flow reversal process (single pump).
In summary, I see no issue, really, with SNA for SDHD, provided her medical team monitors your wifes’ bloods. They are also by far the best placed to know her fistula, its’ foibles (if any), and which of the two options is likely best for her.
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