A Simple, Standard Method to Characterize Pressure/Flow Performance of Vascular Access Cannulas

Vascular access cannulas for extracorporeal life support are
characterized by French (Fr) size alone, which affords limited
information on pressure (P) and flow (Q) performance, making their
selection difficult. Previously, we developed an accurate metric of
cannula performance, the M number, but its complexity and the need of a
nomogram hindered its utility. We propose adoption of an easier and
clinically useful metric to assess cannula performance: Q at 100 mm Hg
P, the updated M number, or the “UM number.” A circuit was created using
a centrifugal pump, Tygon tubing, and a reservoir. A total of 74
cannulas (arterial, venous, and double lumen) ranging from 6 to 50 Fr
size were studied. Glycerol solution with a viscosity of 3 cP was used
to mimic blood. A Biopac system and ultrasonic flow probe was used to
collect P/Q data across a cannula’s performance range. The UM number
describes the pressure-flow characteristics of any given cannula. It can
be used to select access cannulas based on performance and to determine
if flow matches expected flow during use.