Extracorporeal chloride removal to treat acidemia: in vitro evaluation of three techniques

INTRODUCTION. Acidemia is a frequent disorder in critically ill patients. Blood chloride removal may increase blood pH. Extracorporeal chloride removal may be achieved through: 1. Electrodialysis (ED), a technique that selectively move anions from one solution to another through ion-exchange membranes using electricity (1); 2. ultrafiltration (UF) and postdilution with hypochlorous reinfusate; 3. UF through anion Exchange Resin (a-ER) which replaces chloride with bicarbonate ions. OBJECTIVES. To evaluate, in-vitro, the chloride removal efficacy of these three different strategies. METHODS. A standard reinfusate solution (CB 32, Novaselect) (technique 1) and a bicarbonate-based solution (Multibic®) (technique 2 and 3) were pumped through an hemodiafilter at 150 mL/min. The following strategies have been studied: 1. “ED group”: the UF entered an ED chamber where chloride ions were replaced by hydroxide ions (OH-). Subsequently OHions were combined with CO2 to form bicarbonate within a membrane lung and the solution was reinfused in the main stream; 2. “Hypochlorous group”: the UF was discarded and the same volume was reinfused in postdilution as sodium bicarbonate 140 mEq/L; 3. “a-ER group”: the UF was pumped through an a-ER and then reinfused in postdilution. In Hypochlorous and aER groups, UF flows of 11.4, 22.7 and 34.1 mL/ min were tested. In the ED group, 3 different UF flows 15, 30 and 45 mL/min were tested, with a fixed amperage (4 Amp) and recirculating flow was set to equalize the UF tested, to achieve a theoretical removal of 1.25, 2.5, 3.75 mEq/min of chloride, respectively. Before the hemodiafilter and downstream after reinfusion the solution was sampled for UF gas analysis and then wasted. The change in chloride among the two sampling sites was calculated to quantify chloride removal. The experiment was repeated three times. Data are reported as mean±SD. RESULTS. 1. In the “ED group”, chloride removal was 0.47±0.06, 0.96±0.11 and 1.22±0.17 mEq/min at 15, 30 and 45 mL/min of UF flow, respectively. 2. In the “Hypochlorous group”, chloride removal was 1.45±0.09, 2.65±0.09 and 4.50±0.15 mEq/min at 11.4, 22.7 and 34.1 mL/ min of UF flow, respectively. 3. In the “a-ER group”, chloride removal was 1.20±0.15, 2.05±0.09 and 3.35±0.09 at 11.4, 22.7 and 34.1 mL/min of UF flow, respectively (see Figure). CONCLUSIONS. The three different extracorporeal techniques effectively removed chloride. Chloride removal proportionally increased with the rise of the UF flow. Further investigations will be required to confirm these findings and to prove safety and feasibility studies invivo.