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%.