I read the tech note that is available on the crit-line web site, my question is, what happens to the accuracy of the recirc, if a staff member turns the blood pump down. For example, if the blood flow is prescibed for 450 and the staff perform the test at 300, does it increase or decrease or doesn't matter, the % of recirc in the access. Does it matter how far or where the needles are placed, can you pick up arterial stenosis or does the test just find venous stenosis?

Simple answer: Access Recirculation measurements (regardless of type) must be performed at the blood pump speed the patient dialyzes.

More Information: It is essentially a physics problem. For example: Access Blood Flow (ABF) is 300 ml/min, and blood pump speed (Qb) is 400 ml/min. The blood pump will remove 400 ml/min from that access, 300 ml/min will come from the flow to the site, but the other 100 ml/min must be made up from somewhere else. This must happen or the access would collapse. Therefore the other 100 comes from the venous needle - blood that has just been dialyzed. This recirculation of blood is detrimental to both fluid removal and toxin clearance.

If the needles are pointing towards each other obviously it can cause recirculation. However, a recent ASN abstract (A1053 "Is it true the Longer Distance between the Needles, the Less Recirculation in Hemodialysis", W. Huh et al) concluded that "there is no relationship between access recirculation and needle distance."

As to your last question regarding arterial and venous stenosis: These stenoses both cause a reduction in access blood flow - regardless of their location. A stenosis before (arterial) simply reduces the flow downstream and recirculation will occur if the blood pump is removing more blood than is provided by the actual flow at the arterial needle. Venous stenosis simply slows the flow after the venous needle and hence through the entire access. Remember that the flow rate is the same everywhere in the site - if it wasn't the site would expand continously like a balloon !!!

In conclusion, if recirculation is present you know that Access Blood Flow is LESS than blood pump speed. Since DOQI guidelines recommend flows of greater than 600 ml/min - recirculation will not be seen until the access is significantly below the accepted standard. As such recirculation does not have the predicive power of access blood flow, which by definition provides the actual rate of flow present in the access. Over time a trend can be determined and intervention can be performed PRIOR to complete failure.