Structural recirculation and refractory hypoxemia under femoro-jugular veno-venous extracorporeal membrane oxygenation.

The performance of each veno-venous extracorporeal membrane oxygenation (vv-ECMO) configuration is determined by the anatomic context and cannula position. A mathematical model was built considering bicaval specificities to simulate femoro-jugular configuration. The main parameters to define were cardiac output (Q ), blood flow in the superior vena cava (Q ), extracorporeal pump flow (Q ), and pulmonary shunt (k ). The obtained variables were extracorporeal flow ratio in the superior vena cava (EFR  = Q /[Q  + Q ]), recirculation coefficient (R), effective extracorporeal pump flow (Q  = [1 - R] × Q ), Q /Q ratio, and arterial blood oxygen saturation (SaO ). EFR increased logarithmically when Q increased. High Q or high Q /Q decreased EFR (range, 68%-85% for Q of 5 L/min). R also increased following a logarithmic shape when Q increased. The R rise was earlier and higher for low Q and high Q /Q (range, 12%-49% for Q of 5 L/min). The Q /Q ratio (between 0 and 1) was equal to EFR for moderate and high Q . The Q /Q ratio presented the same logarithmic profile when Q increased, reaching a plateau (range, 0.67-0.91 for Q /Q  = 1; range, 0.75-0.94 for Q /Q  = 1.5). The Q /Q ratio was linearly associated with SaO for a given pulmonary shunt. SaO  < 90% was observed when the pulmonary shunt was high (Q /Q  ≤ 0.7 with k  = 0.7 or Q /Q  ≤ 0.8 with k  = 0.8). Femoro-jugular vv-ECMO generates a systematic structural recirculation that gradually increases with Q . EFR determines the Q /Q ratio, and thereby oxygen delivery and the superior cava shunt. EFR cannot exceed a limit value, explaining refractory hypoxemia in extreme situations.