New method for describing the performance of cardiac surgery cannulas

Cardiac surgery cannulas are characterized by external diameter only, which provides little information about the pressure-flow characteristics of a cannula. A system has been developed to describe pressure-flow characteristics with a single, unitless number, M, which is patterned after a Reynolds friction factor correlation. A cannula with a lower M number has a more favorable pressure-flow relationship. The M number was determined for 16 arterials cannulas ranging in size from 10F to 26F and 27 venous cannulas sized 12F to 36F. Pressure-flow characteristics vary considerably among cannulas from different manufacturers despite having similar French sizes. Clinical decisions regarding choice of cannula can be simplified by using the M number, which gives a more accurate description of the performance characteristics of a cannula than the French size designation.