A simple method to estimate phosphorus mobilization in hemodialysis using only predialytic and postdialytic blood samples

Abstract

We have recently developed a pseudo one-compartment model to describe intradialytic and postdialytic rebound kinetics of plasma phosphorus. In this model, individual patient differences in phosphorus kinetics were characterized by a single parameter; the phosphorus mobilization clearance (K(M) ). In this work, we propose a simple method to estimate K(M) from predialytic and postdialytic plasma phosphorus concentrations. Clinical data were collected from 22 chronic hemodialysis patients that underwent a 4-hour treatment session. A simple algebraic equation was derived from the pseudo one-compartment model to determine K(M) from predialytic and postdialytic plasma phosphorus concentrations. K(M) values computed using this equation were compared with values obtained from nonlinear regression of the full kinetic model to frequent intradialytic and postdialytic measurements of plasma phosphorus concentrations. There was good agreement between K(M) values (concordance correlation coefficient of 0.94) obtained from the simple method (105 ± 52 mL/min, mean ± SD) and from the full model (99 ± 47 mL/min). The 95% confidence interval for the difference between estimated K(M) values was -26 to 36 mL/min. The proposed simple method requires the use of only predialytic and postdialytic blood samples to estimate patient specific K(M) ; this approach may allow easy clinical evaluation of phosphorus kinetics in hemodialysis patients.

Patient‐specific phosphorus mobilization clearance during nocturnal and short daily hemodialysis

“…In the nocturnal HD study, K M and V PRE were simultaneously estimated from the intradialytic and postdialytic rebound kinetics of plasma phosphorus concentration using nonlinear regression or least‐squares fitting as described elsewhere . That approach for determining K M cannot be used in the short daily HD study because intradialytic and postdialytic rebound blood samples were not taken during those treatments; instead, K M was estimated during this later study from predialytic and postdialytic plasma phosphorus concentrations by using the following formula: …”

“…It has been proposed that one‐compartment models can be employed with variable phosphorus generation rates or that two‐compartment models can be extended to include additional generation rate terms into a four‐compartment model; however, none of these models have yet proven clinically useful. We have recently developed and evaluated a novel pseudo one‐compartment model that describes phosphorus kinetics during and in the postdialytic rebound period after conventional (4‐hour) or short (2‐hour) HD treatments . In this model, the phosphorus mobilization rate from other body compartments into extracellular fluids was formulated as the difference between predialytic and instantaneous plasma phosphorus concentrations multiplied by a phosphorus mobilization clearance (K M ).…”

“…We have recently developed and evaluated a novel pseudo one-compartment model that describes phosphorus kinetics during and in the postdialytic rebound period after conventional (4-hour) or short (2-hour) HD treatments. 19,20 In this model, the phosphorus mobilization rate from other body compartments into extracellular fluids was formulated as the difference between predialytic and instantaneous plasma phosphorus concentrations multiplied by a phosphorus mobilization clearance (KM). In this study, we have evaluated KM in patients being treated with thrice weekly in-center nocturnal and short daily HD therapies to determine whether this kinetic model can be used to characterize plasma phosphorus kinetics during these alternative HD modalities.…”

Modifications to bicarbonate conductivity: A way to increase phosphate removal during hemodialysis? Proof of concept

“…The primary endpoint was the ability to mobilize phosphate from the intracellular space and interstitium into the plasma: that is, phosphate “refilling.” To quantify this, phosphate mobilization clearance (K M ) was calculated using previously reported methods: where K M is phosphate mobilization clearance (in mL/min); C T0 is serum phosphate at the beginning of the session; C T4h is serum phosphate (in mmol/L) at the end of the session (at T‐4h, in mmol/L); Q UF is ultrafiltration flow rate (in L/h); K D is dialyzer clearance (in mL/min), calculated using the following formula: where C D is dialysate phosphate concentration (in mmol/L); Q D is the dialysate flow rate (in mL/min); and C T1h is serum phosphate at T‐1h (in mmol/L).…”

Phosphorus Kinetics during Hemodiafiltration: Analysis Using a Pseudo-One-Compartment Model

“…When the dialyzer phosphorus clearance is known but only the predialysis and postdialysis serum phosphorus concentrations are measured, it is possible to estimate K M , but not V [16]. In the data reported by Lornoy et al [9] during both HDF and high-flux HD, the predialysis and postdialysis serum phosphorus concentrations were measured as well as total phosphorus removal during each treatment.…”