Background: Recent evidence suggests a better reduction rate of some uremic toxins with expanded hemodialysis (HDx). Methods: Prospective study including 8 hemodialysis patients. We divided the study in 2 phases; within the first one, we assigned 4 patients (group 1) to undergo online hemodiafiltration with a PF 210H dialyzer, and the other 4 patients (group 2) to undergo HDx with the high retention onset Theranova 500 dialyzer during 24 sessions. Later, during the second phase and after a washout period, the same patients were switched to receive HDx (group 1) and HDF (group 2). Results: No differences were found in the Urea and β2-microglobulin reduction ratio. However, in the case of myoglobin, the reduction ratio with HDF was 35 vs. 60% with HDx (p < 0.001). Similarly, in the case of prolactin, the reduction ratio with HDF was 45 and 61% with HDx (p < 0.001). Conclusions: We conclude that HDx is not inferior to online hemodiafiltration in the clearance of small and middle molecules and could be superior in the clearance of larger middle molecules.

Metabolic acidosis correction is achieved by the transfer of bicarbonate and other buffer anions in dialysis. The aim of this study was to evaluate changes in the main anions of intermediary metabolism on standard hemodiafiltration (HDF) and on acetate-free biofiltration (AFB). A prospective, in-center, crossover study was carried out with 22 patients on maintenance dialysis. Patients were randomly assigned to start with 12 successive sessions of standard HDF with bicarbonate (34 mmol/L) and acetate dialysate (3 mmol/L) or 12 successive sessions of AFB without base in the dialysate. Acetate increased significantly during the standard HDF session from 0.078 ± 0.062 mmol/L to 0.156 ± 0.128 mmol/L (P < 0.05) and remained unchanged at 0.044 ± 0.034 mmol and 0.055 ± 0.028 mmol/L in AFB modality. Differences in the acetate levels were observed at two hours (P < 0.005), at the end (P < 0.005) and thirty minutes after the session between HDF and AFB (P < 0.05). There were significantly more patients above the normal range in HDF group than AFB group (68.1% vs 4.5% P < 0.005) postdialysis and 30 minutes later. Serum lactate and pyruvate concentrations decreased during the sessions without differences between modalities. Citrate decreased only in the AFB group (P < 0.05). Acetoacetate and betahydroxybutyrate increased in both modalities, but the highest betahydroxybutyrate values were detected in HDF (P < 0.05). The sum of postdialysis unusual measured organic anions (OA) were higher in HDF compared to AFB (P < 0.05). AFB achieves an optimal control of acid-base equilibrium through a bicarbonate substitution fluid. It also prevents hyperacetatemia and restores internal homeostasis with less production of intermediary metabolites.

The study confirms the hypothesis that TCs have more malfunctions and a lower malposition-free survival rate than SLCs, and TCs are considered as the highest risk factor for malfunction during all study periods.

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