EC CO2R: oxygenator or hemodialyzer? An in vitro study.

In respiratory support of patients with acute respiratory distress syndrome (ARDS), the extracorporeal CO2 removal (EC CO2R) technique should be the earliest and easiest procedure so as to have the lowest blood flow rate. Extracorporeal circulation (ECC) can be achieved using an oxygenator for CO2 removal under the dry form (dissolved CO2) or a hemodialyser for CO2 removal under the wet form (bicarbonates). This study investigated different methods allowing an increase in CO2 transfer, using liquid flow rates up to 0.330 l/min. The experimental set-up employed heated (38 degrees C) aqueous polyelectrolytic solutions mimicking the venous blood (pH 7.20, PCO2 53 mmHg). Four in vitro methods were tested: Series I: a DIDECO D702 oxygenator without blood (= liquid) acidification, Series II: D702 oxygenator with inlet HCl acidification, Series III: a HOSPAL H10-10 hemodialyzer without dialysate alkalinisation, Series IV: H10-10 hemodialyzer with NaOH dialysate alkalinisation. Maximum gas flow in the oxygenator and dialysate rate in hemodialyzer were 5 and 0.55 l/min respectively. For the four series the CO2 transfer (TCO2) (mean +/- S.E. ml/min) and pH out were: [table: see text] The difference between the four series was statistically significant (t-test). Acidification using the oxygenator increased CO2 transfer by 80%, but CO2 elimination was better with hemodialysis.