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 CO 2 removal and reduction of minute mechanical ventilation under extracorporeal respiratory support.Methods: All patients who benefited from V-V ECMO and high-flow ECCO 2 R in our intensive care unit over a period of 18 months were included. CO 2 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 L 2 /min 2 ) and CO 2 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. CO 2 removal was 393 ml/min (IQR, 310-526) for 1.8 m 2 oxygenators and 179 ml/min (IQR, 165-235) for 1.3 m 2 oxygenators. The decarboxylation index was associated linearly with CO 2 removal (R 2 = 0.62 and R 2 = 0.77 for the two oxygenators, respectively) and EC MV ratio (R 2 = 0.72 and R 2 = 0.62, respectively). The 20L 2 /min 2 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 m 2 oxygenators, and between 62% and 38% for 1.3 m 2 oxygenators. Conclusion:The decarboxylation index is a simple parameter to predict CO 2 removal and EC MV ratio under extracorporeal respiratory support.

PCO2 Gradient Between Inlet and Outlet Blood of Extracorporeal Respiratory Support Is a Reliable Marker of CO2 Elimination

“…Extracorporeal respiratory support via V-V ECMO or ECCO 2 R is used increasingly in critically ill setting. [6][7][8][9]28,29 Determinants of extracorporeal decarboxylation are numerous: oxygenator surface, sweep gas flow, pre-oxygenator PCO 2 , but also Q EC as demonstrated recently by Laumon et al [10][11][12][13][14] In clinical practice, consideration of all these parameters helps to predict CO 2 elimination under extracorporeal respiratory support, which is based on changes of CO 2 content into extracorporeal circulation. However, the equations determining CO 2 content in blood are old and complex, and were established in a healthy population.…”

“…In a previous work, we demonstrated that the product sweep gas flow × Q EC reliably predicts CO 2 elimination; this is the prescribed decarboxylation index. 14 However, its predictive value is robust only in the absence of oxygenator alterations or other confounding factors. In contrast, current study has assessed the delivered decarboxylation index; the ∆ EC PCO 2 × Q EC product was found to be linearly associated with the amount of CO 2 that was removed by extracorporeal support (model 5); each additional unit of the ∆ EC PCO 2 × Q EC product predicted an increase in CO 2 elimination of 5.2 ml STPD/min.…”

“…Several of these patients were studied previously to assess the performance of the product of Q EC × sweep gas flow in predicting minute ventilation reduction. 14…”

“…These two types of devices perform extracorporeal decarboxylation, which is influenced by many determinants; the mains are extracorporeal pump flow (Q EC ), oxygenator surface, sweep gas flow, inlet PCO 2 . [10][11][12][13][14] Although normalizing PCO 2 seems usually simpler to obtain than systemic oxygenation with extracorporeal respiratory support, [15][16][17] decarboxylation may be challenging or insufficient in some cases or require several devices. 18,19 Moreover, the oxygenator membrane deteriorates with use, leading to a progressive reduction in its performance in terms of CO 2 elimination.…”