Impact of membrane lung surface area and blood flow on extracorporeal CO 2 removal during severe respiratory acidosis

Veno-venous extracorporeal CO removal (vv-ECCO R) is increasingly being used in the setting of acute respiratory failure. Blood flow rates through the device range from 200 ml/min to more than 1500 ml/min, and the membrane surface areas range from 0.35 to 1.3 m . The present study in an animal model with similar CO production as an adult patient was aimed at determining the optimal membrane lung surface area and technical requirements for successful vv-ECCO R. Four different membrane lungs, with varying lung surface areas of 0.4, 0.8, 1.0, and 1.3m were used to perform vv-ECCO R in seven anesthetized, mechanically ventilated, pigs with experimentally induced severe respiratory acidosis (pH 7.0-7.1) using a 20Fr double-lumen catheter with a sweep gas flow rate of 8 L/min. During each experiment, the blood flow was increased stepwise from 250 to 1000 ml/min. Amelioration of severe respiratory acidosis was only feasible when blood flow rates from 750 to 1000 ml/min were used with a membrane lung surface area of at least 0.8 m . Maximal CO elimination was 150.8 ml/min, with pH increasing from 7.01 to 7.30 (blood flow 1000 ml/min; membrane lung 1.3 m ). The membrane lung with a surface of 0.4 m allowed a maximum CO elimination rate of 71.7 mL/min, which did not result in the normalization of pH, even with a blood flow rate of 1000 ml/min. Also of note, an increase of the surface area above 1.0 m did not result in substantially higher CO elimination rates. The pressure drop across the oxygenator was considerably lower (