HDF and pump speed

I dialyse in centre 3 times P’s using Fresenius with HDF
I use pump speed of 300, blood chemistry is said to be “ spot “
I also have aortic valve problem
The unit Sister is urging me to increase pump speed saying that I could get better clearance and that HDF facilitates higher speeds without any adverse effects
I find this difficult to believe because higher speed must mean higher blood flow with impact on heart valves
Any comment please
Thanks David1942

David you have to understand that the blood flow threw your lower arm runs between 6 hundred to 8 hundred ml per minute. Your upper arm runs form 8 hundred to 2 thousand so if you increase the blood flow to 400 it should cause no harm, that being said ask your Dr about it.

Stuart, thanks for your response, however that raises also the point that my understanding from John Ager is that he recommends max speed of 350 pref 300, a dictum that I have followed for years and found my blood chemistry to be excellent. Is that advice now changed?
It seems to me that faster speeds give better clearance but at some sacrifice54 to heart valve performance.

Also my question was is it correct that speed can be higher with HDF than HD with zero negative effect.

The data would suggest that there is little summative benefit to clearance from higher and higher flow beyond about 350. We tend to run max flows for our 15 hr/week in-facility patients at about 325. In our home patients who are mainly on between 30-40 hrs/week, we run 225-250 by preference. You may find a blog … and especially the graph of flow rate vs clearance … helpful … see https://www.homedialysis.org/news-and-research/blog/228-blood-flow-rate-fistula-integrity-and-optimal-clearance

If you study this graph, you will see that the increase in clearance flattens out as flow rates exceed about 300 - 325 and ramping up the flow further and further achieves only minor clearance benefit.

But, higher flow rates do carry risk. As blood flows increase, so too does the return jet increase and the turbulence created can lead to vein wall damage … see that same blog. While the total flow/minute is commonly in excess of 1000 ml/min = far in excess of the return blood flow from the dialysis system, this is largely linear flow inside an arterialised vein. Meanwhile, the return flow - be it 250, 300, 350, 400, or whatever - while it is a far lesser volume than the linear venous flow it re-joins, returns as a non-linear, often tangential, and pulsatile whooosh/whooosh/whooosh from the venous return needle. This impacts the cells the line the vein wall and can set up vibratory harmonics in the upstream vein segment. This can promote vein wall damage and stenoses. For these reasons, we like to keep flow rates at a rather less furious pace and not push it higher, just for the sake of it.

On the subject of your aortic valve, I doubt that your fistula flow rates - whether they be 300 or 400 (or more) - will have too much of an effect (if any) on your aortic valve. There is no additive flow. The same total volume that was flowing into the fistula before the arterial needle removed a percentage is reconstituted in the venous limb to on-flow to the heart.

Let’s work through a rather simplistic example. Let’s assume the base fistula flow is 1000 ml/min. Then, let’s run the blood pump at 300 ml/min. As the machine ‘robs’ 300 ml/min from the arterial needle to direct through the machine, a flow of 700 ml/min will be left in the fistula to proceed onward past the arterial needle within the fistula to the venous limb. But, if the blood flow is 450 ml/min and the machine ‘robs’ 450 ml/min to redirect through the machine, 550 ml/min will proceed past the arterial needle within the fistula to the venous limb.

When dialysed blood is returned back from the machine to the venous end of the fistula through the venous needle, this is simply recombining the two separated volumes and restoring the blood volume in the venous end of the fistula to its original volume … minus, that is, any small per minute UF volume that has been removed at the dialyser.

So … the volume at either end of the fistula will only have changed by the amount that has been ultra-filtered in the dialyser.

It is not any (small) change in fistula flow volume that matters, but rather it is the amount of turbulence, of eddying, that is set up as the venous blood is returned that matters … and that IS clearly speed-of-flow related. But by the time the blood has reached back into the central circulation, most of this eddying and turbulence has settled down. By the time the blood makes it back through the right heart, the lungs, and thence to the left heart, any/all effect on flow is zero. So, on that score, and in respect of a repaired aortic valve - protected as it is from any direct dialysis influences behind the triple firewalls of the right heart chambers, the lung circulation, and left heart chambers - I think you can rest easy.

As blood flow rates in HD and HDF? … the same arguments hold. While there may be a small increase in small solute clearance generated by a higher blood flow rate in HDF c/w HD, the main advantages are generated through enhanced convective clearance as established by manipulation of the dialysis fluid volumes and pressures, not through any differences in blood flow rates. While I have to say that we like HDF in our service, and all our in-facility patients are now on HDF (though our home patients are not), blood flow rates are not the reason why better clearance occurs. For an explanation of the benefits of and reasons behind HDF, can I suggest you read the KidneyViews blog at … https://www.homedialysis.org/news-and-research/blog/135-explaining-haemodiafiltration-hdf

Finally, if you feel fine and your numbers are fine, then you are likely also doing fine. I’d leave it be.