Switching from Three Times a Week to Short Daily Online Hemodiafiltration: Effects on Acid-Base Balance

Abstract

Aims

This study examines the effect of a change from the standard 4–5 hours 3 times a week of online hemodiafiltration (OL-HDF) to 2–2.5 hours daily (6 times a week) OL-HDF, on acid-base balance, and attempts assess the modifications of acid-base parameters, ionic concentration, and electrical charges of albumin and phosphate available for diffusion and convection mechanisms across the membrane and subsequent infusion.

Methods

In 18 patients on online HDF, blood gas, electrolytes (Na, K, Cl), lactate, phosphate, albumin, apparent strong ion difference (SIDa), effective strong ion difference (SIDe), strong ion gap (SIG), anion gap (AG), and bicarbonate and pH time-averaged concentration (TAC) and time-averaged deviation (TAD) variables were evaluated at baseline, and 1, 3, 6, 9, and 12 months after patients were switched to daily OL-HDF. Additionally, in 12 patients, the same parameters measured simultaneously at dialyzer inlet, outlet, and after reinfusion were studied.

Results

Throughout the study, weekly single-pool Kt/V, equilibrated Kt/V, and TAC urea remained constant. However, standard Kt/V increased and TAD urea decreased on daily OL-HDF. There were no statistical differences during the time span of 12 months in pH, cations (Na, K), anions (Cl, HCO^–₃ AG, and lactate), or SIDa, SIDe, and SIG pre-HDF; while pH and HCO₃^– TAD decreased from 0.02 and 1.02 ± 0.74 mEq/L, to 0.01 and 0.64 ± 0.52 mEq/L, respectively (p<0.01). Net albumin charge and AG increased significantly at dialyzer outlet and decreased after reinfusion.

Conclusions

We did not observe changes in the acid-base balance in patients who switched from 3 times a week to short daily OL-HDF. The main benefit observed was a lower pH and bicarbonate TAD. This shows a better physiology for daily OL-HDF.