Extracorporeal carbon dioxide removal through ventilation of acidified dialysate : an experimental study

BACKGROUND: Extracorporeal (EC) carbon dioxide (CO2) removal (ECCO2R) may be a powerful alternative to ventilation, possibly avoiding the need for mechanical ventilation and endotracheal intubation. We previously reported how an infusion of lactic acid before a membrane lung (ML) effectively enhances ECCO2R. We evaluated an innovative ECCO2R technique based on ventilation of acidified dialysate. METHODS: Four swine were sedated, mechanically ventilated, and connected to a venovenous dialysis circuit (blood flow, 250 ml/min). The dialysate was recirculated in a closed loop circuit including a ML (gas flow, 10 liters/min) and then returned to the dialyzer. In each animal, 4 different dialysis flows (DF) of 200, 400, 600, and 800 ml/min were evaluated with and without lactic acid infusion (2.5 mEq/min); the sequence was completed 3 times. At the end of each step, we measured the volume of CO2R by the ML (Vco2ML) and collected blood and dialysate samples for gas analyses. RESULTS: Acid infusion substantially increased Vco2ML, from 33 ± 6 ml/min to 86 ± 7 ml/min. Different DFs had little effect on Vco2ML, which was only slightly reduced at DF 200 ml/min. The partial pressure of CO2 of blood passing through the dialysis filter changed from 60.9 ± 3.6 to 37.1 ± 4.8 mm Hg without acidification and to 32.5 ± 5.3 mm Hg with acidification, corresponding to a pH increase of 0.18 ± 0.03 and 0.03 ± 0.04 units, respectively. CONCLUSIONS: Ventilation of acidified dialysate efficiently increased ECCO2R of an amount corresponding to 35% to 45% of the total CO2 production of an adult man from a blood flow as low as 250 ml/min.