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(C)), blood flow in the superior vena cava (Q(SVC)), extracorporeal pump flow (Q(EC)), and pulmonary shunt (k(S-PULM)). The obtained variables were extracorporeal flow ratio in the superior vena cava (EFRSVC = Q(EC)/[Q(EC) + Q(SVC)]), recirculation coefficient (R), effective extracorporeal pump flow (Q(eff-EC) = [1 - R] x Q(EC)), Q(eff-EC)/Q(C) ratio, and arterial blood oxygen saturation (SaO(2)). EFRSVC increased logarithmically when Q(EC) increased. High Q(C) or high Q(SVC)/Q(C) decreased EFRSVC (range, 68%-85% for Q(EC) of 5 L/min). R also increased following a logarithmic shape when Q(EC) increased. The R rise was earlier and higher for low Q(C) and high Q(SVC)/Q(C) (range, 12%-49% for Q(EC) of 5 L/min). The Q(eff-EC)/Q(C) ratio (between 0 and 1) was equal to EFRSVC for moderate and high Q(EC). The Q(eff-EC)/Q(C) ratio presented the same logarithmic profile when Q(EC) increased, reaching a plateau (range, 0.67-0.91 for Q(EC)/Q(C) = 1; range, 0.75-0.94 for Q(EC)/Q(C) = 1.5). The Q(eff-EC)/Q(C) ratio was linearly associated with SaO(2) for a given pulmonary shunt. SaO(2) < 90% was observed when the pulmonary shunt was high (Q(eff-EC)/Q(C) <= 0.7 with k(S-PULM) = 0.7 or Q(eff-EC)/Q(C) <= 0.8 with k(S-PULM) = 0.8). Femoro-jugular vv-ECMO generates a systematic structural recirculation that gradually increases with Q(EC). EFRSVC determines the Q(eff-EC)/Q(C) ratio, and thereby oxygen delivery and the superior cava shunt. EFRSVC cannot exceed a limit value, explaining refractory hypoxemia in extreme situations.