Table 1.

Rule of 6s: Sonographic criteria for AVF maturation.

CRITERIADESCRIPTION
Outflow vein calibre ≥6 mm on ultrasoundOutflow veins will progressively dilate over time. Generally, a calibre of 6 mm is indicative of an outflow vein that is easy to cannulate and will provide sufficient flow for hemodialysis
Outflow vein depth <6 mm on ultrasoundIf outflow veins are too deep within the subcutaneous tissues, they may be difficult to cannulate. Those that are too deep may require further surgery for superficialization
Blood flow >600 mL/minSufficient blood flow is required through the outflow vein to support adequate hemodialysis
Cannulation >6 wk postcreationIt is often best to wait at least 6 wk postcreation before cannulating an AVF to allow it to arterialize appropriately. This can minimize cannulation-related complications such as hemorrhage or false aneurysms
  • AVF—arteriovenous fistula.