Simulation of potassium extraction by continuous haemodiafiltration.

Prediction of potassium extraction rates by continuous haemodiafiltration (CHDF) is useful for safe management of potassium levels in patients with hyperkalaemia. For this purpose, we developed a formula to predict the quantity of potassium extracted by CHDF. We hypothesized that potassium concentration in efflux dialysate was completely saturated by the influx blood, and potassium concentration in efflux blood was calculated based on this hypothesis. To check the accuracy of the calculation, potassium concentration was measured in efflux blood, and values were compared to predicted concentrations. Predicted potassium concentrations demonstrated good correlation to the measured values (95% confidence range, -0.32 to 0.58 mmol/l). These results confirmed that our hypothesis is applicable to clinical use of CHDF. Based on our observations, we created a formula to accurately predict the amount of potassium (dK) extracted by CHDF: dK=(Cb-Cd)xQd+CbxQf-CsxQs (Cb: plasma potassium concentration; Cd: potassium concentration in a dialysate; Cs: potassium concentration in the replacement fluid; Qd: dialysis rate; Qf: filtration rate and Qs: infusion rate of replacement fluid).