Fistula

Velocities

  • Peak systolic velocities in fistulas are typically high and should be at least 150 cm/s throughout
  • Arterial anastomosis stenosis is suspected if ratio between the highest outflow velocity to inflow arterial velocity ratio is > 3.0
    • Anastomotic velocity greater than 400 cm/s with Vr > 3.0 (ratio between highest anastomotic velocity and inflow artery PSV 2 cm proximal to anastomosis) suggests >50% stenosis
  • Velocity ratio between any contiguous segments should be < 2.0
    • Other segments with PSV 300-400, EDV > 240, and Vr of > 2.0 is suggestive of a >50% stenosis

Flow Volume

  • Volume flow should be generally > 500 mL/min regardless of type of AV access
  • Ideal flow is 800 to 1200 mL/min
  • Flow volume calculated by cross section area x time-averaged velocity x 60 seconds
    • < 450 mL/min is indicative of poor dialysis, patency limited for prosthetic graft, although native AVF may remain patent
    • > 500 mL/min Normal AVF
    • > 700 mL/min Normal AV graft
    • > 1400 mL possible high output heart failure