Abstract
BACKGROUND: Hyperphosphatemia in the hemodialysis population is ubiquitous, but phosphate kinetics during hemodialysis is poorly understood.
METHODS: Twenty-nine hemodialysis patients each received one long and one short dialysis, equivalent in terms of urea clearance. Phosphate concentrations were measured during each treatment and for one hour thereafter. A new model of phosphate kinetics was developed and implemented in VisSim. This model characterized additional processes involved in phosphate kinetics explaining the departure of the measured data from a standard two-pool model.
RESULTS: Pre-dialysis phosphate concentrations were similar in long and short dialysis groups. Post-dialysis phosphate concentrations in long dialysis were higher than in short dialysis (P < 0.02) despite removal of a greater mass of phosphate (P < 0.001). In both long and short dialysis serum phosphate concentrations initially fell in accordance with two-pool kinetics, but thereafter plateaued or increased despite continuing phosphate removal. Implementation of an additional regulatory mechanism such that a third pool liberates phosphate to maintain an intrinsic target concentration (1.18 +/- 0.06 mmol/L; 95% confidence intervals, CI) explained the data in 24% of treatments. The further addition of a fourth pool hysteresis element triggered by critically low phosphate levels (0.80 +/- 0.07 mmol/L, CI) yielded an excellent correlation with the observed data in the remaining 76% of treatments (cumulative standard deviation 0.027 +/- 0.004 mmol/L, CI). The critically low concentration correlated with pre-dialysis phosphate levels (r=0.67, P < 0.0001).
CONCLUSION: Modeling of phosphate kinetics during hemodialysis implies regulation involving up to four phosphate pools. The accuracy of this model suggests that the proposed mechanisms have physiological validity.
Original language | English |
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Pages (from-to) | 655-67 |
Number of pages | 13 |
Journal | Kidney International |
Volume | 61 |
Issue number | 2 |
DOIs | |
Publication status | Published - Feb 2002 |
Keywords
- Adult
- Aged
- Aged, 80 and over
- Female
- Humans
- Kidney Failure, Chronic
- Male
- Middle Aged
- Models, Biological
- Phosphates
- Renal Dialysis
- Urea
- Journal Article