Simple and accurate quantification of dialysis in acute renal failure patients during either urea non-steady state or treatment with irregular or continuous schedules.

Abstract

The quantification of dialysis in critically ill acute renal failure (ARF) patients requires a unifying expression that can establish kinetic equivalence amongst patients treated with irregular or frequent intermittent haemodialysis (IHD) schedules or with differing renal replacement therapies. EKRjc is a generalized form of the equivalent urea renal clearance (EKRc), and represents the equivalent continuous urea clearance that will result in the given time-averaged concentration of urea, for the given amount of urea removal. The suitability of EKRjc for the measurement of dialysis dose in this setting is examined. 420 weeks of renal replacement therapy (IHD and continuous renal replacement therapy) were simulated in 15 virtual 'patients' using a variable volume double pool urea kinetic model. Additional data from eight ARF patients were used to exemplify calculations. 1260 EKRjc values were calculated using both formal urea kinetic modelling, as well as a simplified method that requires input of changes in patient fluid state and blood urea nitrogen concentrations over a period of observation, in addition to an initial estimate of patient post-dialysis urea distribution volume (V(T)). EKRjc is shown to provide a unifying expression of dialysis dose irrespective of IHD schedule or renal replacement therapy. EKRjc is shown to be independent from the assumption of the urea steady state, and intrinsically normalized to patient urea distribution volume to allow dose comparisons between patients of different size. Residual renal urea clearance is easily incorporated where present. EKRjc is easily calculated using the simplified method without the need for iterative urea kinetic modelling. The accuracy of this simplified method is maintained when the initial estimation of V(T) is both 25% greater or smaller than the true value. Calculation of EKRjc is exemplified using the clinical data. EKRjc is the most suitable urea kinetic expression for the quantification of dialysis in critically ill ARF patients.