Introduction of a switch that can reverse blood flow direction on-line during hemodialysis.

In several circumstances in hemodialysis, the regular direction of blood flow has to be reversed or changed, such as in access dysfunction or insufficient blood flow being obtained through the arterial port, as well as to measure actual access blood flow in fistulas or grafts by using the formula Qa = Qb((1-R)/R), where R represents recirculation in the reversed line configuration. We invented a disposable switch device made from standard blood line tubing that can be introduced into the dialysis circuit and allows for on-line reversal of lines, without needing to manually disconnect and reconnect tubing or interrupt the hemodialysis procedure. Over a period of eight months, 16 patients (8 arteriovenous fistula, 8 PTFE) underwent 193 hemodialysis sessions with the switch in place. Circuit pressures, pump, and actual blood flows measured with ultrasound dilution were monitored before and after reversing the lines. Switching was accomplished within 1-2 seconds. Arterial circuit (r = 0.99), venous circuit pressures (r = 0.6), and actual pump flow (364 +/- 56 vs. 350 +/- 57 ml/min; r = 0.73) correlated very well preswitching and postswitching (p < 0.0001). Dialysis circuit flow measured with an ultrasound dilution technique decreased from 364 +/- 56 (230-480) ml/min preswitching to 350 +/- 57 (220-490) ml/min postswitching (p < 0.001). No difficulties or complications were observed. This switch device is a useful addition to the technology of hemodialysis in that it greatly facilitates the procedure of reversing the lines in an extracorporeal circuit while not significantly interfering with circuit pressures and connections.