Phosphate Kinetics in Hemodialysis: Application of Delayed Pseudo One-Compartment Model.

ABSTRACT

BACKGROUND/AIMS: Various body-regulating mechanisms try to counteract rapid changes in serum phosphate levels during hemodialysis (HD). Neither recently proposed nor other existing standard compartment models are able to capture clinically observed intradialytic serum phosphate rebound. METHODS: Phosphate serum concentration was frequently measured during 75 HD sessions in 25 patients. Time delay was introduced into the standard pseudo one-compartment model in order to reflect the time needed for the body-regulating mechanism to affect serum phosphate level. RESULTS: Measured serum phosphate concentration at the end of 4 h dialysis session was on average larger than 1 h earlier (p value = 0.015). The model with time delay reproduced successfully 19 out of 21 and 9 out of 10 sessions with and without recorded intradialytic rebound, respectively. CONCLUSION: The intradialytic serum phosphate rebound is associated with the time delay reflecting efficacy of body-regulating mechanisms, that is, the larger the delay the larger is the intradialytic rebound.