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


METHODS
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.
Renal (MedicalProducts), Baxter Healthcare Corporation, McGaw Park, Illinois, USA.
Baris U
BU
Agar
Alp
A
Akonur
Ying-Cheng
YC
Lo
Alfred K
AK
Cheung
John K
JK
Leypoldt
D000328:Adult; D000368:Aged; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D010758:Phosphorus / Q000378:metabolism*; D006435:Renal Dialysis; D015203:Reproducibility of Results; D013997:Time Factors
D010758:Phosphorus