Relationship between ionic dialysance and urea blood water clearance

Introduction: ionic dialysance is a method of continuous on-line monitoring of delivered dialysis without blood sampling. To compare the results obtained by ionic dialysance and those obtained by the traditional measurements of the dialysis dose, it is necessary to know the relationship between the ionic dialysance and urea clearance. Material and methods: Ionic dialysance and the urea clearance were determined in 18 patients (13 dialyzed with cuprophan and 5 patients with AN69). Urea clearance was measured by 6 different methods: urea clearance in whole blood calculated with the arteriovenous difference in the urea concentration rates and the arterial flow measured by the rolling pump (KBAVb) or by ultrasounds (KBAVu); urea clearance in whole blood measured by the urea concentration in the dialysate (KBD); urea blood water clearance measured by the arteriovenous difference in the concentration rates using the arterial flow measured by the roller pump (KwBAVb) or by ultrasounds (KwBAVu) and urea blood water clearance measured by the urea concentration in dialysate (KwBD). Results: The mean arterial flow measured by the roller pump was 314.4 +/- 16.2 ml/inin and 275.1 +/- 13.8 ml/min when measured by ultrasounds (p < 0.001). The data of ionic dialysance and urea clearances were as follow (ml/min): ionic dialysance 185,6 +/- 17.7; KBAVb 245.7 +/- 15.7; KBAu 215.4 +/- 13.2; KBD 231.6 +/- 13.1; KwBAVb 218.1 +/- 14; KwBAVu 191.2 +/- 11.8; KwBD 183.1 +/- 11.7. The absolute difference of ionic dialysance with the KwBAVu was 8.4 +/- 6 ml/min (range between -17.8 and 11.5 mi) and with the KwBD was 7.6 +/- 5.4 mi (range between -12.9 and 21.4 ml). Conclusions: There was a relationship between ionic dialysance and urea blood water clearance. The best concordance was obtained when the clearance was calculated with the urea concentration of dialysate, or with the arteriovenous difference of the urea concentration rates and the arterial blood flow measured by ultrasounds.