Accuracy and safety of online clearance monitoring based on conductivity variation

Background. Haemodialysis dose has been shown to have a distinct impact upon the morbidity and mortality rate in patients on regular dialysis therapy. Accordingly, the adequacy of dialysis treatment should be guaranteed. Methods. In 200 dialysis sessions two or three ± 10% dialysate conductivity variations were applied to test patient compliance and the accuracy of an electrolyte based online clearance measurement (OCM) reflecting the total clearance of urea. Results. Using a step profile the electrolytic clearance showed highly significant correlation with the reference data in the blood side (n = 118, r = 0.867, P<0.001) and dialysate side (n = 118, r = 0.820, P < 0.001) if only reference values were taken into account for which the error in mass balance did not exceed 5%. Kt/V according to the single pool model (n = 35, r = 0.940, P < 0.001), the equilibrated single pool variable volume kinetic model (n = 36, r = 0.982, P < 0.001), Daugirdas formula (n = 34, r = 0.951, P < 0.001) and direct quantification of dialysance via spent dialysate (n = 26, r = 0.900, P < 0.001) showed outstanding correlations with electrolyte-based Kt/ V at mass balance error below 5%, No adverse clinical effect of OCM was reported. Serum sodium, body weight, heart rate and breathing rate at rest, arterial pO 2 and pCO 2 and blood pressure before haemodialysis remained unaffected in OCM measurements in comparison with baseline parameters. A small influx of sodium (1.53 ± 7.62 mmol) into the patient was seen following the impulse, but no signs associated with fluid overload were observed during the study period of 10 consecutive dialysis sessions. Conclusions. The OCM option of the haemodialysis machine provides a safe and accurate tool for continuous online monitoring of total urea clearance.