IN-VIVO MEASUREMENT OF HEMODIALYZER FIBER BUNDLE VOLUME - THEORY AND VALIDATION

Background. Fiber bundle volume (FBV), the space within the blood comp artment of hollow fiber dialyzers, may decrease during treatment due t o clotting. The clots may be flushed out of the dialyzer prior to meas urements of FBV by dialyzer reprocessing equipment and a significant d rop in FBV during the session may go unrecognized. Methods. FBV was me asured (I) from the transit time of a saline bolus passing through the dialyzer as recorded by ultrasound dilution sensors placed on the art erial and venous blood lines; (2) from the change in blood concentrati on induced by a step change in the rate of ultrafiltration as recorded by the venous sensor. Results. In vitro FBV ranged from 47 to 121 mi. Paired absolute differences between the ultrasound and volumetric mea surements (flushing saline out of the dialyzer into a graduated cylind er) were 0.16 +/-: 4.23% (N = 42) and 2.10 +/- 7.26% (N = 13) for the bolus and ultrafiltration methods, respectively. In vivo reproducibili ty of the bolus and ultrafiltration methods were 2.65 +/- 2.11% (N = 1 22) and 3.79 +/- 3.93% (N = 32), respectively. During 31 treatments th e FBV by dilution showed an average decrease of 4.17 +/- 8.60%, and in 6 cases FBV fell more than 10%, while measurements of the same FBV by reuse equipment showed an increase of 0.99 +/- 5.82%, P < 0.01. Concl usions. FBV measured by the dilution methods was accurate and reproduc ible. Preliminary results suggest that in vivo FBV may differ signific antly from results reported by reprocessing machines.