Calcium balance in pediatric online hemodiafiltration: Beware of sodium and bicarbonate in the dialysate.

Background: Online hemodiafiltration (oHDF) is increasingly used in children; we treated 28 children since 2009, adapting this technique to pediatric patients.

Methods: In this service evaluation audit, we assessed plasma electrolytes to evaluate the evolution of total (tCa) and ionized (iCa) during a session, as well as dialysate calcium (dCa) concentrations.

Results: Using a 1.25 mmol Ca/L-dialysate, both tCa and iCa decreased during the session, with iCa falling below 1.1 mmol/L in 4/5 patients. In contrast, using a 1.5 mmol Ca/L-dialysate, iCa remained normal in all patients. Major discrepancies were observed between the expected and the measured dCa: 1.25 vs. 1.01 (0.83-1.04), and 1.5 vs. 1.47 (0.85-1.75) mmol/L, respectively (results presented as median [range]). These differences were explained by the modality of reconstituting dialysate: increasing bicarbonates and/or decreasing sodium requested in the dialysate decreases calcium extraction from the acid preparation. Proof of concept was given when requesting in an "ex-vivo" setting modifications in the requested sodium and bicarbonate in dialysate directly on the Fresenius machine.

Conclusion: Nephrologists should be aware that "high bicarbonate and/or low sodium" requirements in oHDF decrease calcium in the dialysate.