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

Abstract

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 ECCO2R 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 (ECMV 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 ECMV 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 ECMV 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 ECMV ratio under extracorporeal respiratory support.