Blood acidification enhances carbon dioxide removal of membrane lung: an experimental study

Extracorporeal CO2 removal is an effective procedure to allow a protective ventilatory strategy in ARDS patients, but it is technically challenging due to the high blood flow required. Increasing the CO2 transfer through the membrane lung (ML) may lower the demand of extracorporeal blood flow and consequently allow for a wider clinical application of this technique. Since only the dissolved CO2 (5% of the total CO2 content) is easily removed by the ML, we tested whether acidifying the blood entering the ML to convert bicarbonate ions towards dissolved CO2 could enhance the CO2 transfer though the ML.

Six pigs were connected to an extracorporeal circuit comprising a ML. The extracorporeal blood flow was 500 ml/min, while the gas flow was 10 l/min. A 15-min continuous infusion of 0.5 N lactic acid was added to the extracorporeal blood flow before the ML at a rate of 1, 2 and 5 mEq/min. Between steps we waited for a reequilibration time of at least 30 min.

Acid infusion at 0, 1, 2 and 5 mEq/min increased pCO2 (56.19 +/- 7.92, 68.24 +/- 11.73, 84.28 +/- 11.17 and 136.66 +/- 18.46 mmHg, respectively) and decreased pH (7.39 +/- 0.05, 7.30 +/- 0.05, 7.20 +/- 0.05 and 6.91 +/- 0.05, respectively). ML CO2 removal increased 11, 23 and 70% during acid infusion at 1, 2 and 5 mEq/min, respectively.

Blood acidification at the inlet of a ML with infusion of 1, 2 and 5 mEq/min of lactic acid can increase the CO2 removal capacity of the ML up to 70%.