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. 2011 Dec;6(12):2854-60.
doi: 10.2215/CJN.03860411. Epub 2011 Oct 27.

Kinetic model of phosphorus mobilization during and after short and conventional hemodialysis

Baris U Agar  1 , Alp Akonur, Ying-Cheng Lo, Alfred K Cheung, John K Leypoldt
Affiliations

Kinetic model of phosphorus mobilization during and after short and conventional hemodialysis

Baris U Agar et al. Clin J Am Soc Nephrol. 2011 Dec.

Abstract

Background and objectives: The kinetics of plasma phosphorus (inorganic phosphorus or phosphate) during hemodialysis treatments cannot be explained by conventional one- or two-compartment models; previous approaches have been limited by assuming that the distribution of phosphorus is confined to classical intracellular and extracellular fluid compartments. In this study a novel pseudo one-compartment model, including phosphorus mobilization from a large second compartment, was proposed and evaluated.

Design, setting, participants, & measurements: Clinical data were obtained during a crossover study where 22 chronic hemodialysis patients underwent both short (2-hour) and conventional (4-hour) hemodialysis sessions. The model estimated two patient-specific parameters, phosphorus mobilization clearance and phosphorus central distribution volume, by fitting frequent intradialytic and postdialytic plasma phosphorus concentrations using nonlinear regression.

Results: Phosphorus mobilization clearances varied among patients (45 to 208 ml/min), but estimates during short (98 ± 44 ml/min, mean ± SD) and conventional (99 ± 47 ml/min) sessions were not different (P = 0.74) and correlated with each other (concordance correlation coefficient ρ(c) of 0.85). Phosphorus central distribution volumes for each patient (short: 11.0 ± 4.2 L and conventional: 11.9 ± 3.8 L) were also correlated (ρ(c) of 0.45).

Conclusions: The reproducibility of patient-specific parameters during short and conventional hemodialysis treatments suggests that a pseudo one-compartment model is robust and can describe plasma phosphorus kinetics under conditions of clinical interest.

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Figures

Figure 1.
Figure 1.
Different schematic representations of the proposed phosphorus kinetic model. (A) Two-compartment model with inaccessible phosphorus represented as a separate large compartment. (B) The pseudo one-compartment model. CPRE, predialytic plasma phosphorus concentration; C, instantaneous plasma phosphorus concentration; V, volume of accessible compartment for phosphorus; KM, phosphorus mobilization clearance; KD, dialyzer phosphate clearance.
Figure 2.
Figure 2.
Plasma phosphorus concentration during and 1 hour after short hemodialysis (SHD) (solid line) and conventional hemodialysis (CHD) (dotted line) treatments (n = 21). SD values are shown on the positive side for SHD and on the negative side for CHD. Statistical comparisons between SHD and CHD show no differences at t = 0 minutes (P = 0.96), t = 30 minutes (P = 0.35), or t = 60 minutes (P = 0.15).
Figure 3.
Figure 3.
Percentage of rebound of plasma phosphorus concentration after short hemodialysis (SHD) (solid line) and conventional hemodialysis (CHD) (dotted line) treatments (n = 21). SD values are shown on the positive side for SHD and on the negative side for CHD. Statistical comparisons between CHD and SHD indicate no differences at t = 2 minutes (P = 0.56), t = 10 minutes (P = 0.99), t = 30 minutes (P = 0.56), or t = 60 minutes (P = 0.84).
Figure 4.
Figure 4.
Modeled and measured plasma phosphorus concentrations for a typical patient (patient no 4) during short hemodialysis (SHD) and conventional hemodialysis (CHD) sessions.
Figure 5.
Figure 5.
Comparison of parameter estimates obtained from short hemodialysis (SHD) and conventional hemodialysis (CHD) treatments. The identity lines represent equality between parameter estimates. VPRE, volume of accessible compartment for phosphorus; KM, phosphorus mobilization clearance.
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Comment in

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