Residual renal function in incremental haemodialysis

Equivalent renal clearance (EKR) and standard clearance (stdK) are continuous-equivalent measures of urea clearance and include residual renal function (RRF), if calculated appropriately. RRF is qualitatively better than dialysis with equivalent urea clearance. Instructions for calculating stdKt/V (stdK scaled by urea distribution volume) and its target value (2.3) are presented in the Kidney Disease Outcomes Quality Initiative (KDOQI) 2015 guidelines. EKR targets have not been defined in the current guidelines.

The stdKt/V in the presence of RRF was calculated with the classic double-pool urea kinetic model and with the Daugirdas modification, which accentuates the renal contribution. The EKR/V (EKR scaled by urea distribution volume) was calculated with nominal and adjusted renal clearance (renal urea clearance multiplied by a weighting factor). New prescriptions with different continuous clearance targets were generated by a computer program.

The contribution of RRF can be weighted flexibly in EKR/V by adjusting the renal clearance value. A new therapeutic index, EKR/V _a (adjusted total EKR/V), was introduced. In 62 incremental dialysis sessions of 16 patients with a renal urea clearance (K_r) of over 1 mL/min, the Daugirdas stdKt/V was, on average, 7.5% higher than classic stdK/V and adjusted EKR/V was 14.4% higher than unadjusted EKR/V.

The stdKt/V is not an optimal descriptor of haemodialysis urea clearance. With EKR/V, the role of RRF can be evaluated more sensibly. Using adjusted EKR/V as the target permits less frequent incremental dialysis.