New research challenges the common assumption that high flow rates during venoarterial extracorporeal membrane oxygenation (VA-ECMO) increase pulmonary capillary wedge pressure (PCWP) and the risk of pulmonary oedema in patients with cardiogenic shock. The ECMO-Flow trial found that increasing VA-ECMO flow often has a neutral or even beneficial effect on PCWP, despite raising left ventricular afterload.¹

The ECMO-Flow trial was a prospective, single-centre interventional study conducted in Paris, France, involving 80 patients with cardiogenic shock who were stabilised on femoro-femoral VA-ECMO support. The study protocol involved stepwise variations in VA-ECMO flow, increasing from 2 to 4 L/min in 0.5 L/min increments. The primary objective was to evaluate the impact of these flow variations on PCWP. Comprehensive assessments included measurements from a pulmonary artery catheter, transthoracic echocardiography, and blood gas analyses to monitor haemodynamic and echocardiographic parameters.

At baseline, 27 patients (34%) had a PCWP of 18 mm Hg or higher. The study found that as VA-ECMO flow was incrementally increased, PCWP decreased in 29 patients (36%) and remained stable in 46 patients (58%). An increase in PCWP was observed in only 5 patients (6%). This occurred despite a concurrent rise in left ventricular (LV) afterload.

Further haemodynamic analysis revealed that central venous pressure (CVP) significantly decreased with increased flow, while right ventricular (RV) afterload remained unchanged. Indexed stroke volume also decreased, and myocardial work remained stable. A significant decrease in PCWP was more commonly observed in patients who had better baseline LV and RV function and lower CVP.

These findings suggest that the physiological response to increased VA-ECMO flow is more complex than previously thought. The expected rise in PCWP due to increased afterload appears to be effectively counterbalanced by a reduction in RV preload. This mechanism results in a neutral or favourable outcome for PCWP in the majority of patients with cardiogenic shock. The management of VA-ECMO flow may not inherently lead to worsening pulmonary congestion, a key concern in LV unloading strategies.²

The investigators concluded that “as VA-ECMO flow increases, the expected rise in PCWP caused by afterload elevation appears to be counterbalanced by a reduction in RV preload, resulting in a neutral effect in most patients, a significant PCWP decrease in approximately one-third, and an only infrequent increase.”¹

References

1. Saura O, Hékimian G, Del Marmol G, et al. Effect of ECMO Flow Variations on Pulmonary Capillary Wedge Pressure in Patients With Cardiogenic Shock. JACC. 2025;86(11):768–778. https://doi.org/10.1016/j.jacc.2025.06.048

2. Ezad SM, Ryan M, Donker DW, et al. Unloading the left ventricle in venoarterial ecmo: in whom, when, and how? Circulation. 2023;147:1237-1250. https://doi.org/10.1161/CIRCULATIONAHA.122.062371

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