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

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 (QC ), blood flow in the superior vena cava (QSVC ), extracorporeal pump flow (QEC ), and pulmonary shunt (kS-PULM ). The obtained variables were extracorporeal flow ratio in the superior vena cava (EFRSVC =QEC /[QEC +QSVC ]), recirculation coefficient (R), effective extracorporeal pump flow (Qeff-EC =[1-R]×QEC ), Qeff-EC /QC ratio, and arterial blood oxygen saturation (SaO2 ).

RESULTS: EFRSVC increased logarithmically when QEC increased. High QC or high QSVC /QC decreased EFRSVC (range, 68%-85% for QEC of 5 L/min). R increased also following a logarithmic shape when QEC increased. The R rise was earlier and higher for low QC and high QSVC /QC (range, 12%-49% for QEC of 5 L/min). The Qeff-EC /QC ratio (between 0 and 1) was equal to EFRSVC for moderate and high QEC . The Qeff-EC /QC ratio presented the same logarithmic profile when QEC increased, reaching a plateau (range, 0.67-0.91 for QEC /QC =1; range, 0.75-0.94 for QEC /QC =1.5). The Qeff-EC /QC ratio was linearly associated with SaO2 for a given pulmonary shunt. SaO2 <90% was observed when the pulmonary shunt was high (Qeff-EC /QC ≤0.7 with kS-PULM =0.7 or Qeff-EC /QC ≤0.8 with kS-PULM =0.8).

CONCLUSION: Femoro-jugular vv-ECMO generates a systematic structural recirculation that gradually increases with QEC . EFRSVC determines the Qeff-EC /QC ratio, and thereby oxygen delivery and the superior cava shunt. EFRSVC cannot exceed a limit value, explaining refractory hypoxemia in extreme situations.