Assessment of intradialysis calcium mass balance by a single pool variable‐volume calcium kinetic model

Abstract

Introduction: A reliable method of intradialysis calcium mass balance quantification is far from been established. We herein investigated the use of a single-pool variable-volume Calcium kinetic model to assess calcium mass balance in chronic and stable dialysis patients.Methods: Thirty-four patients on thrice-weekly HD were studied during 240 dialysis sessions. All patients were dialyzed with a nominal total calcium concentration of 1.50 mmol/L. The main assumption of the model is that the calcium distribution volume is equal to the extracellular volume during dialysis. This hypothesis is assumed valid if measured and predicted end dialysis plasma water ionized calcium concentrations are equal. A difference between predicted and measured end-dialysis ionized Correspondence to: S. Di Filippo, Division of Nephrology, A. Manzoni Hospital, Via dell'Eremo 9/11, 23900 Lecco, Italy. Email: difilippo.salvatore@libero.it Conflict of Interest: The Authors have nothing to disclose with regards of the present manuscript. Disclosure of grants or other funding: None List of abbreviations: 0-t, Initial and final values; Ca21d, Ionized dialysate calcium concentrations (mmol/L); Ca21di, Dialysate calcium concentration (mmol/L) at the inlet port of dialyzer; Ca21MB, Intra-dialysis ionized calcium mass balance (mmol); Ca21pw, Ionized plasma water calcium concentrations (mmol/L); Ca21pwi, Plasma water calcium concentration (mmol/L) at the inlet port of dialyzer; Ca21pwtM, End-dialysis measured plasma water calcium concentration (mmol/L) normalized at pH 7.40; Ca21pwtP, End-dialysis plasma water calcium concentration (mmol/L) predicted by the model; Ca21pwt(P-M), Difference between end-dialysis plasma water calcium concentration predicted and measured (mmol/L); Ca21uf, Outlet ultrafiltrate stream calcium concentration (mmol/L) normalized at pH 7.40; CaMB, Intra-dialysis global calcium mass balance (mmol); D 0 Ca, Calcium dialysance (L/min) corrected for cardiopulmonary and access recirculation; D 0 cond, Conductivity dialysance (L/ min) corrected for cardiopulmonar and access recirculation; KoAcond, "Intrinsic" dialysance for conductivity (mL/min); MCa21, Mobilization of calcium from extracellular fluid compartment (mmol); Na1d, Ionized dialysate sodium concentrations (mmol/L); Na1pw, Ionized plasma water sodium concentrations (mmol/L); Qbi, Inlet blood flow (mL/min); Qei, Inlet blood water flow (mL/min); Qdi, Inlet dialysate flow (mL/min); Cdi, Inlet dialysate conductivity (mS/cm); Qf, Total ultrafiltrate (L); QfECW, Ultrafiltrate removed from the extracellular fluid compartment (L/min); Qpwi, Inlet plasma water flow (L/min); SPVVCaKM, Single-compartment variable-volume calcium kinetic model; SPVV-NaKM, Single-compartment variable-volume sodium kinetic model; Td, Dialysis session duration (min); VCat, End-dialysis calcium distribution volume (L); Vut, End dialysis urea distribution volume (L); spKt/V, Single Pool Kt/V; a, Donnan factor Predialysis ionized plasma water concentration and total ultrafiltrate were the most imp...

Dialysate Calcium Levels: Do They Matter?

“…However, in different studies, both a positive and negative DCa were observed during a DCa of 3.0 mEq/L [34,35]. Other studies have showed that the use of a DCa of 2.5 mEq/L had in general a neutral effect on SCa levels, but with variable effects on CaMB [36].…”

“…In the context of the DialysIS study, a more rigorous method capable of quantifying the intradialytic CaMB was proposed [35]. The proposed single-pool variablevolume kinetic model, tested in patients treated with a DCa concentration of either 3.0 or 3.5 mEq/L took into account all aspects of diffusive and convective exchange using bicarbonate dialysis.…”

“…The choice of the optimal DCa deserves a thoughtful process, taking into account the cardiovascular status, parameters of mineral metabolism, the concomitant use of drugs such as Pbinders, cinacalcet or vitamin D analogues and the hemodynamic stability of the patient. Direct measurement of CaMB during dialysis is difficult to achieve on a daily clinical basis, but the introduction of kinetic models appears easier to implement [7,8,33,35]. More research should focus on the optimal DCa taking into account the individual patient, making the treatment an optimal tailor-made treatment.…”

A Bayesian approach for the identification of patient-specific parameters in a dialysis kinetic model

“…calcium, potassium and phosphorus, that play a crucial role for hydro-electrolyte equilibria. [16][17][18] To achieve more effective prediction models, multi-pool models have been introduced, allowing to describe the simultaneous contribution of different plasma solutes. 19 However, none of these models aim at characterizing the patientspecific solute kinetics in HD, apart from Ursino et al, 19 in which an individual estimation of few parameters characterizing solute kinetics has been performed.…”

“…This fact is proved by the presence of kinetic models specific for calcium. 16 We now consider the LFO case. The marginal posterior densities of the patient-specific parameters for these tests, compared with the true values used to generate the simulated datasets, are reported in Tables 4-6.…”