Performance of the decarboxylation index to predict CO₂ removal and minute ventilation reduction under extracorporeal respiratory support

Background: The aim of this study was to assess the interdependence of extracorporeal blood flow (Qec) and gas flow (GF) in predicting CO₂ removal and reduction of minute mechanical ventilation under extracorporeal respiratory support.

Methods: All patients who benefited from V-V ECMO and high-flow ECCO₂ R in our intensive care unit over a period of 18 months were included. CO₂ removal was calculated from inlet/outlet blood port gases during the first 7 days of oxygenator use. The relationship between the Qec × GF product (named decarboxylation index and expressed in L² /min² ) and CO₂ removal or expired minute mechanical ventilation reduction (_EC MV ratio) was studied using linear regression models.

Results: Eighteen patients were analyzed, corresponding to 24 oxygenators and 261 datasets. CO₂ removal was 393 ml/min (IQR, 310-526) for 1.8 m² oxygenators and 179 ml/min (IQR, 165-235) for 1.3 m² oxygenators. The decarboxylation index was associated linearly with CO₂ removal (R² = 0.62 and R² = 0.77 for the two oxygenators, respectively) and _EC MV ratio (R² = 0.72 and R² = 0.62, respectively). The 20L² /min² value (considering Qec = 2 L/min and GF = 10 L/min) was associated with an _EC MV ratio between 61% and 29% for 1.8 m² oxygenators, and between 62% and 38% for 1.3 m² oxygenators.

Conclusion: The decarboxylation index is a simple parameter to predict CO₂ removal and _EC MV ratio under extracorporeal respiratory support.