Physiologic Effects of Extracorporeal Membrane Oxygenation in Patients with Severe Acute Respiratory Distress Syndrome

Rationale: Blood flow rate affects mixed venous oxygenation (SvO2) during venovenous extracorporeal membrane oxygenation (ECMO), with possible effects on the pulmonary circulation and the right heart function. Objectives: To describe the physiologic effects of different levels of SvO2 obtained by changing ECMO blood flow in patients with severe acute respiratory distress syndrome receiving ECMO and controlled mechanical ventilation. Methods: Low (SvO2 target, 70–75%), intermediate (SvO2 target, 75–80%), and high (SvO2 target, .80%) ECMO blood flows were applied for 30 minutes in random order in 20 patients. Mechanical ventilation settings were left unchanged. The hemodynamic and pulmonary effects were assessed with pulmonary artery catheter and electrical impedance tomography. Measurements and Main Results: Cardiac output decreased from low to intermediate and to high blood flow/SvO2 (9.2 [6.2–10.9] vs. 8.3 [5.9–9.8] vs. 7.9 [6.5–9.1] L/min; P = 0.014), as well as mean pulmonary artery pressure (34 6 6 vs. 31 6 6 vs. 30 6 5 mm Hg; P, 0.001) and right ventricular stroke work index (14.2 6 4.4 vs. 12.2 6 3.6 vs. 11.4 6 3.2 g 3 m/beat/m2; P = 0.002). Cardiac output was inversely correlated with mixed venous and arterial PO2 values (R2 = 0.257; P = 0.031; and R2 = 0.324; P = 0.05). Pulmonary artery pressure was correlated with decreasing mixed venous PO2 (R2 = 0.29; P, 0.001) and with increasing cardiac output (R2 = 0.378; P, 0.007). Measures of V/ _ Q_ mismatch did not differ between the three steps. Conclusions: In patients with severe acute respiratory distress syndrome, increased ECMO blood flow rate resulting in higher SvO2 decreases pulmonary artery pressure, cardiac output, and right heart workload.