CVC blood flow rate

I was wondering if anyone knew what you should set the bloodflow rate at when running a patient via a CVC line when you have to reverse the lines due to poor flow. Someone told me that you shouldn't run it faster than like 250ml/min due to increased recirculation with reversed arterial/venous lines, but no one else I have asked has ever heard of this being a standard practice. So if the ordered flow rate is 400ml/min, and say the arterial line will not withdraw (thus the need to reverse the lines), and when I reverse the lines the flow is great (so it is possible to achieve 400ml/min if I choose) what should I set the flow at so that the patient gets the optimal dialysis?