Comparison between ionic dialysance and small molecule clearance with different dialyzers

Recently, the measurement of the effective ionic dialysance has been proposed as an accurate method for on-line monitoring of dialysis dose. The aim of the present study was to assess the effective clearance simultaneously with the measurement of the ionic dialysance with different dialyzers, and compare the urea and creatinine clearance with the effective ionic dialysance. Twelve stable patients on regular dialysis therapy were studied prospectively. All patients had an arterio-venous fistula recently performed and still had a jugular or subclavian catheter. To avoid recirculation the arterial line was connected to the arteriovenous access and the venous line to the catheter. The effective ionic dialysance was obtained with a specially designed module equipped with a single conductivity probe to measure the changes in conductivity of delivered dialysate. Blood samples and the spent dialysate during 2'15 " were simultanously collected. Urea and creatinine concentration were determined in blood and dialysate to calculate the clearance of both molecules. These measurements were performed at blood flow rates of 200, 300 and 400 ml/min, with two different dialyzers, hemophan and polysulfone. The effective ionic dialysance, and the urea and creatinine clearances increased proportionaly with elevation of the blood flow rate. Al the three blood flow rates studied the mean value of urea clearance was higher than effective ionic dialysance and creatinine clearance (p < 0.01), and the mean value of creatinine clearance was lower than effective ionic dialysance (p < 0.01). A significant correlation was observed between effective ionic dialysance and both urea (r = 0.82, p < 0.01) and creatinine clearance (r = 0.83, p < 0.01). Furthermore a good correlation was found between the urea and creatinine clearance (r = 0.85, p < 0.01). We did not find any difference between hemophan and polysulfone membrane clearance. In conclusion, the on-line monitoring of ionic dialysance is an accurate method for the determination of effective dialyzer clearance. In addition, this conductivity method provides a very useful tool for monitoring the effective dose of dialysis delivered in each dialysis session without the need for blood sampling and biochemical determinations.