Quantitative assessment of sodium mass removal using ionic dialysance and sodium gradient as a proxy tool: comparison of high-flux hemodialysis versus online hemodiafiltration.

BACKGROUND Restoration and maintenance of sodium is still a matter of concern and remains of critical importance to improve outcomes in homeostasis of stage 5 chronic kidney disease patients on dialysis. Sodium mass balance and fluid volume control rely on the 'dry weight' probing approach consisting mainly in adjusting ultrafiltration volume and diet restrictions to patient needs. An additional component of sodium and fluid management relies on adjusting the dialysate-plasma sodium concentration gradient. Hypotonicity of ultrafiltrate in online hemodiafiltration (ol-HDF) might represent an additional risk factor in regard to sodium mass balance. METHODS A continuous blood-side approach for quantifying sodium mass balance in hemodialysis and ol-HDF using online ionic dialysance sensor device ("Flux" method) embedded on hemodialysis machine was explored and compared to conventional cross-sectional "Inventory" methods using anthropometric measurement (Watson), multifrequency bioimpedance analysis (MF-BIA) or online clearance monitoring (OCM®) to assess total body water. An additional dialysate-side approach, consisting in the estimation of inlet/outlet sodium mass balance in the dialysate circuit was also performed. Ten stable hemodialysis patients were included in a "ABAB"-designed study comparing high-flux hemodialysis (hf-HD) and ol-HDF. Results are expressed using a patient-centered sign convention, as follows: accumulation into the patient leads to a positive balance while recovery in the external environment (dialysate, machine) leads to a negative balance. RESULTS In the blood-side approach, a slight difference in sodium mass transfer was observed between models with hf-HD (-222.6 [-585.1-61.3], -256.4 [-607.8-43.7], -258.9 [-609.8-41.3] and -258.5 [-607.8-43.5] mmol/session with Flux and Inventory models using VWatson , VMF-BIA and VOCM values for volumes of total body water respectively; global p-value <0.0001) and ol-HDF modalities (-235.3 [-707.4-128.3], -264.9 [-595.5-50.8], -267.4 [-598.1-44.1] and -266.0 [-595.6-55.6] mmol/session with Flux and Inventory models using VWatson , VMF-BIA and VOCM values for volumes of total body water respectively; global p-value <0.0001). Cumulative net ionic mass balance on a weekly basis remained virtually similar in hf-HD and ol-HDF using Flux method (p=n.s.). Finally, the comparative quantification of sodium mass balance using blood-side (Ionic Flux) and dialysate-side approaches reported clinically acceptable i) agreement (with limits of agreement with 95% confidence intervals (CI): -166.2 to 207.2) and ii) correlation (Spearman rho=0.806; p<0.0001) CONCLUSIONS: We validated a new method to quantify sodium mass balance based on ionic mass balance in dialysis patients by using embedded ionic dialysance sensor combined with dialysate/plasma sodium concentrations. This method is accurate enough to support care givers in managing sodium mass balance in dialysis patients. It offers a bridging solution to automated sodium proprietary balancing module of hemodialysis machine in the future.