Measurement of fiber bundle volume in reprocessed dialyzers

Fiber bundle volume (FBV) is an important determinant of dialyzer re-use efficiency. This measurement is performed after the dialyzer has been pressure cleaned and may underestimate the degree of clotted fibers a patient actually encounters while on dialysis.

Real-time online measure of FBV has been validated using an ultrasound dilution method and the Transonic HD01 monitor (Ithaca, NY, USA). Thirty-one stable chronic hemodialysis patients were studied during the first hour and then during the last 30 minutes of a typical dialysis session. Ultrasound velocity curves using a saline bolus were recorded by flow dilution sensors placed directly on the blood tubing using methods described previously. Blood volume within the dialyzer compartment was determined using a mathematical extrapolation of the measured transit time for a bolus of saline to pass through the dialyzer. These data were compared to FBV obtained using a Seartronics DRS4 (Fresinius, Walnut Creek, CA, USA) reprocessing machine both before and after the same dialysis session.

At onset of treatment mean FBV by ultrasound was 100.0 +/- 2.7 ml and was unchanged at the end of the session at 100.0 +/- 3.1 ml (p = 0.49). Before a dialysis session, mean FBV measured on the DRS4 reprocessing machine was 123.5 +/- 2.1 ml and was unchanged following cleaning after dialysis at 121.7 +/- 2.0 ml (p = 0.20). The correlation coefficient between methods was 0.78.

FBV did not change during a dialysis session using an online real-time measure. The results of this study do not support concerns that hemodialysis patients may experience considerably less efficient dialysis than standard FBV determination would suggest due to undetected clotting.