Development of a Method for Measuring Hemodialysis Access Flow: From Idea to Robust Technology

Briefly reversing the blood lines during hemodialysis by returning the dialyzed (venous) blood upstream from the inflow port creates artificial access recirculation, the magnitude of which is a function of access blood flow. A method was recently introduced for measuring access blood flow by reversing the blood lines and applying classic indicator dilution techniques (1, 2). The indicator is a bolus of isotonic saline and the detector is an ultrasound probe that, when clamped to the blood tubing, can simultaneously measure blood flow in the tubing and detect changes in ultrasound velocity induced by the saline bolus (Fig. 1) ( 3 ) . Key to this procedure is reversal of the blood lines, a maneuver that could theoretically be accomplished by simply reversing the blood pump, but the latter technology has not yet been developed. The mathematical translation of access recirculation during temporary reversal of the lines to access flow (Qa) is: