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

Abstract

Background The performance of each veno‐venous extracorporeal membrane oxygenation (vv‐ECMO) configuration is determined by the anatomic context and cannula position. Methods 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 (EFR_SVC=Q_EC/[Q_EC+Q_SVC]), recirculation coefficient (R), effective extracorporeal pump flow (Q_eff‐EC=[1–R]×Q_EC), Q_eff‐EC/Q_C ratio, and arterial blood oxygen saturation (SaO₂). Results EFR_SVC increased logarithmically when Q_EC increased. High Q_C or high Q_SVC/Q_C decreased EFR_SVC (range, 68%–85% for Q_EC of 5 L/min). R increased also 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 EFR_SVC 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 SaO₂ for a given pulmonary shunt. SaO₂ 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). Conclusion Femoro‐jugular vv‐ECMO generates a systematic structural recirculation that gradually increases with Q_EC. EFR_SVC determines the Q_eff‐EC/Q_C ratio, and thereby oxygen delivery and the superior cava shunt. EFR_SVC cannot exceed a limit value, explaining refractory hypoxemia in extreme situations.