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.

Abnormal electrical stimulus of an intra-aortic balloon pump with concurrent support with continuous veno-venous hemodialysis.

Malfunction of electronic medical support apparatus utilized in the ICU usually causes system failure. We report several occurrences of a potentially dangerous interaction between a continuous veno-venous hemodialysis (CVVHD) system and an intra-aortic balloon pump (IABP) counterpulsation device in four patients requiring both systems. The patients had acute renal failure in the face of multi-organ failure and were dependent upon the balloon pump for pressure support. Electrical interference created by the roller pump action of the CVVHD system was identified by the balloon pump as cardiac in origin, and it responded by inflation and deflation. As the blood pump rate was reduced, the interference reduced to the point of complete cessation when the blood pump was shut down. Whereas one patient transiently had a significant drop of mean arterial pressure (from 70 +/- 4 to 40 +/- 2 mm Hg) the other observed occurrences had no clinically significant sequelae. Electrocardiogram (ECG) tracings identified the abnormal stimulus and systematic review identified as potential sources for the creation of this interference static electricity buildup, piezoelectric properties of the polyvinyl chloride tubing, and, possibly but less likely, radiofrequency interference. A newer generation ECG cable and advanced cardiac rhythm recognition software (CardioSync) have been introduced with the Datascope System 98, and the ECG interference, although still occasionally present, does not cause erratic inflation and deflation of the intra-aortic balloon pump. Interference between different electrical support systems may occur, and we suggest that the systems be tested for compatibility before combined use and that older equipment be more rigorously tested for potential clinically significant interference.