Residual renal function in incremental dialysis

Abstract

Incremental haemodialysis has the potential to allow better preservation of renal function, is less invasive to the patient and has lower cost. Despite these advantages, it is not commonly applied. This may be due to uncertainty about how to account for renal function in the prescription of dialysis and measurement of dose. In this issue, Vartia describes the practical basis for including the effect of renal function in the prescription and quantification of dialysis. He uses a well-known and validated urea kinetic model to calculate time average urea concentrations and the equivalent renal clearance (EKR) from dialysis. The effect of renal function is amplified by a weighting factor to account for the relatively greater effect of renal function compared with dialysis with the same urea clearance. In that way, patients on differing dialysis regimens can be dialysed with the same target dose. A further step would be to use a downward adjusting factor for dialysis to convert the urea clearance by dialysis (as EKR) to a glomerular filtration rate (GFR) equivalent. A factor of 0.75 is suggested. In that way, dialysis dose can be reported as GFR equivalent in mL/min/1.73 m², comparable between different types of dialysis and also to renal function without dialysis.

Keywords: GFR; incremental dialysis; renal function.

FIGURE 1

Incremental dialysis to maintain GFR equivalent to 10mL/min. The patient develops uraemic symptoms at year 4 when GFR decreases to <8mL/min/1.73 m². At that point, low-dose dialysis is started to boost GFR equivalent to 10mL/min and the patient becomes asymptomatic. Thereafter, dialysis dose is regularly increased to maintain GFR equivalent at this level as renal function decreases.