Normally the rate of blood flow through an arteriovenous (AV) access and particularly an AV graft is about 1 l per minute. During hemodialysis, the blood is pumped through the dialysis machine at rates up to 500 cc per minute leading to a flow differential. This results in the desired circumstance of only blood from the arterial side of the access entering the blood pump. However, if flow through the access is decreased significantly, such as in decreased arterial inflow, some of the blood from the venous cannula will be taken up again through the arterial cannula in order to support the set rate of flow of the blood pump, resulting in recirculation.

Another common cause of recirculation is the presence of a high-grade venous stenosis, in which case, the outflow is restricted, and some of the blood leaving the venous cannula cycles back to the arterial cannula and results in recirculation.

Other causes of access circulation can result from improper technique of needle placement. In some centers, this has been found to be responsible for the great majority of recirculation in their patient population [2]. Close proximity or misdirection of arterial and venous needle placement, especially in new vascular access due to a lack of familiarity with the access anatomy will result in access recirculation. Misdirection of needle placement can be corrected by good communication with the access surgeon or establishing arterial versus venous limbs of the access. Arterial and venous limbs can be differentiated easily by occluding the access at the midpoint, and the side with a pulse is the arterial limb.