Phosphate kinetics during hemodialysis: Evidence for biphasic regulation

Elaine M Spalding, Paul W Chamney, Ken Farrington

Research output: Contribution to journalArticlepeer-review

135 Citations (Scopus)

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 languageEnglish
Pages (from-to)655-67
Number of pages13
JournalKidney International
Volume61
Issue number2
DOIs
Publication statusPublished - 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

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