You can rise Kt/V by using a Qd up to 600 ml/min. I think it is more expensive than usefull , but we may try in some case.
Dear Raymond,
The most cost-effective option perhaps is using a flow regulator, keeping automatically the dialysate flow 1.2 times the bloodflow. (Reference Kult J and Stapf E.: Changing emphasis in modern hemodialysis therapies. Cost-effectiveness of delivering higher doses of dialysis. Int J Artif Organs 2007; 30: 577-582)
With best regards:
The optimum dialysate flow depends on your primary goal: If you are limited in dialysate (e.g. using a constant dialysate batch of fixed volume), or dialysate is a cost factor, then even dialysate/blood flow ratios below 1.2 (e.g 1.0 or even 0.8) are an option. Of course, then the treatment duration must be long enough to achieve a sufficient dialysis dose.
As Andre Stragier already pointed out, for a fixed ratio 1.2 is a good choice for cost-effectiveness. We did an international multicenter study using a smart machine with a fixed ratio and a part of the dialysate using as substitution fluid (thus creating additional convective flow across the dialyzer membrane) and even got a higher dialysate dose although we spent less dialysate compared to standard (see Mesic et al. Dialysate savings by automated control... Hemodial Int 2011 (15) 4: 522-9).
Qd = 500 ml/min is used in standard hemodialysis . High efficiency techniques imply a Qd = 700 - 800 ml/min expecially on-line techniques
It depends what you mean by optimal.
1) For the highest possible clearance, the dialysis fluid flow rate should be as high as possible (ideally infinite). This will ensure maximum concentration gradient of uraemic toxins across the dialyser membrane.
2) For the most efficient use of dialysate (i.e. maximizing the mass of solute cleared for every ml of dialysis fluid), the dialysis fluid flow rate should be as low as possible. This will ensure the dialysis fluid will have equilibrated with the blood so that the concentration of uraemic solute in the dialysis fluid will be as high as possible.
Of course these two are in conflict.
A simple way of looking at clearance in dialysis is that it depends on blood flow rate, dialysis fluid flow rate and membrane area, thickness and porosity (quantified as mass transfer area coefficient, MTAC). These three all have units of flow (e.g. ml/minute).
Clearance, K e.g. in in ml/min is most limited by the lowest of the three flows.
For intermittent, out-patient dialysis, the treatment time is effectively limited so K should be as high as possible. MTAC is around 1000 ml/min for a modern dialyser, so clearance is most limited by blood flow and dialysis fluid flow. Blood flow is limited by the access. Dialysis fluid is generated on-line so its flow can be increased relatively easily. To maximise K, blood flow should be as high as the access will allow, and dialysis fluid flow should be significantly higher than blood flow (condition 1). In practice, there are diminishing returns when dialysis fluid flow is more than about 1.2x blood flow rate.
As long as dialysis fluid flow is significantly higher than blood flow, K will be most dependent on blood flow rate.
For continuous dialysis (e.g. PD, CRRT), K does not need to be high, but the dialysis fluid is expensive, so condition 2 applies. Since dialysis fluid flow in this context is much lower than MTAC or blood flow, K is almost equal to dialysis fluid flow (the dialysis fluid has similar concentration of uraemic solute to the blood). Use the lowest dialysis fluid flow required to achieve target K. For continuous HD/HDF the blood flow rate should be significantly higher than dialysis fluid flow rate.
Hi Gulcin
the key point is the differences between kinds of renal replacement therapies.
if you want to access a high kt/v in a short time , you should adjust QB: 300 to 400 cc/min and QD/QB 1.5 to 2 times but sometimes you try to slow down the blood purification due to your patient`s condition . in this case you can set the QD/QB below 1 . in this situation you can , not to slow down the QB due to decrease the risk of coagulation .
Ramin
regards