Blood oxygenation and decarboxylation determinants during venovenous ECMO for respiratory failure in adults.

PURPOSE: This study was designed to optimize the latest generation venovenous (vv)-extracorporeal membrane oxygenation (ECMO)-circuit configuration and settings based on the evaluation of blood oxygenation and CO2 removal determinants in patients with severe acute respiratory distress syndrome (ARDS) on ultraprotective mechanical ventilation.

METHODS: Blood gases and hemodynamic parameters were evaluated after changing one of three ECMO settings, namely, circuit blood flow, FiO(2ECMO) (fraction of inspired oxygen in circuit), or sweep gas flow ventilating the membrane, while leaving the other two parameters at their maximum setting.

RESULTS: Ten mechanically ventilated ARDS patients (mean age 44 ± 16 years; 6 males; mean hemoglobin 8.0 ± 1.8 g/dL) on ECMO for a mean of 9.0 ± 3.8 days) receiving femoro-jugular vv-ECMO were evaluated. vv-ECMO blood flow and FiO(2ECMO) determined arterial oxygenation. Decreasing the ECMO flow from its baseline maximum value (5.8 ± 0.8 L/min) to 40% less (2.4 ± 0.3 L/min) significantly decreased mean PaO2 (arterial oxygen tension; 88 ± 24 to 45 ± 9 mm Hg; p < 0.001) and SaO2 (oxygen saturation; 97 ± 2 to 82 ± 10%; p < 0.001). When the ECMO flow/cardiac output was >60%, SaO2 was always >90%. Alternatively, the rate of sweep gas flow through the membrane lung determined blood decarboxylation, while PaCO2 (arterial carbon dioxide tension) was unaffected when the ECMO blood flow and FiO(2ECMO) were reduced to <2.5 L/min and 40%, respectively. In three additional patients evaluated before and after red blood cell transfusion, O2 delivery increased after transfusion, allowing lower ECMO flows to reach adequate SaO2.

CONCLUSIONS: For severe ARDS patients receiving femoro-jugular vv-ECMO, blood flow was the main determinant of arterial oxygenation, while CO2 elimination depended on sweep gas flow through the oxygenator. An ECMO flow/cardiac output >60% was constantly associated with adequate blood oxygenation and oxygen transport and delivery.