Volumetrical microcomputer-based ultrafiltration monitor for hemodialysis

Uniform and controlled ultrafiltration during hemodialysis can decrease dialysis side effects. One of the prerequisites for this treatment is accurate measurement of ultrafiltration. The best method currently available for ultrafiltration measurement is based on the volumetrically measured change of dialysate flow over the dialyzer. We have developed an ultrafiltration monitor (UFM) for hemodialysis using two micro-oval flowmeters that measure the flow rate of the dialysate entering and leaving the dialyzer. Correction for intrinsic error was achieved with an Acorn microprocessor, in a calibration run without ultrafiltration and constant, equal flow through both flow transducers. The accuracy of the UFM in vitro was 99.4% of the mean total ultrafiltration, with a correlation coefficient of 0.998 (n = 8) with actual ultrafiltration. In vivo, in which UFM was compared with bed scale body weight monitoring, a correlation coefficient of 0.97 (n = 82) was obtained, and an accuracy of 90% of total ultrafiltration as measured by the change in body weight. Therefore, this UFM provides a cheap and reliable method for ultrafiltration measurement.