Mathematical modelling of oxygenation under veno-venous ECMO configuration using either a femoral or a bicaval drainage

Abstract

Background: The bicaval drainage under veno-venous extracorporeal membrane oxygenation (VV ECMO) was compared in present experimental study to the inferior caval drainage in terms of systemic oxygenation.

Method: Two mathematical models were built to simulate the inferior vena cava-to-right atrium (IVC → RA) route and the bicaval drainage-to-right atrium return (IVC + SVC → RA) route using the following parameters: cardiac output (Q_C), IVC flow/Q_C ratio, venous oxygen saturation, extracorporeal pump flow (Q_EC), and pulmonary shunt (PULM-Shunt) to obtain pulmonary artery oxygen saturation (S_PAO₂) and systemic blood oxygen saturation (SaO₂).

Results: With the IVC → RA route, S_PAO₂ and SaO₂ increased linearly with Q_EC/Q_C until the threshold of the IVC flow/Q_C ratio, beyond which the increase in S_PAO₂ reached a plateau. With the IVC + SVC → RA route, S_PAO₂ and SaO₂ increased linearly with Q_EC/Q_C until 100% with Q_EC/Q_C = 1. The difference in required Q_EC/Q_C between the two routes was all the higher as SaO₂ target or PULM-Shunt were high, and occurred all the earlier as PULM-Shunt were high. The required Q_EC between the two routes could differ from 1.0 L/min (Q_C = 5 L/min) to 1.5 L/min (Q_C = 8 L/min) for SaO₂ target = 90%. Corresponding differences of Q_EC for SaO₂ target = 94% were 4.7 L/min and 7.9 L/min, respectively.

Conclusion: Bicaval drainage under ECMO via the IVC + SVC → RA route gave a superior systemic oxygenation performance when both Q_EC/Q_C and pulmonary shunt were high. The VV-V ECMO configuration (IVC + SVC → RA route) might be an attractive rescue strategy in case of refractory hypoxaemia under VV ECMO.

Keywords: Bicaval drainage; Oxygenation determinants; Oxygenation performance; Pulmonary shunt; Rescue therapy; Structural recirculation; Superior cava drainage; Superior cava shunt; Triple cannulation; VV-V configuration.

Fig. 1

Modelling of the IVC → RA and IVC + SVC → RA routes. IVC inferior vena cava, RA right atrium, SaO₂ arterial blood oxygen saturation, S_PAO₂ pulmonary arterial blood oxygen saturation, S_PREO₂ blood oxygen saturation in the drainage cannula(s), SVC superior vena cava

Fig. 2

Relationship between SaO₂ and S_PAO₂ according to pulmonary shunt. When lung function is optimal (PULM-Shunt=0%), SaO₂ is equal to 100% regardless the S_PAO₂ value. In contrast when residual lung function is null (PULM-Shunt=100%), SaO₂ is equal to S_PAO₂. Between these two clinical status, the relationship SaO_{2 *} PULM-Shunt is linear with a slope that directly depends on S_PAO₂. The S_PAO₂ value is the final consequence of ECMO therapy in term of oxygenation. PULM-Shunt pulmonary shunt, SaO₂ arterial blood oxygen saturation, S_PAO₂ pulmonary arterial blood oxygen saturation

Fig. 3

Oxygenation performance of the IVC → RA and IVC + SVC → RA routes. Beyond Q_EC/Q_c = 1 using the IVC⁺SVC → RA route, Q_Eff reaches the Q_c value and cannot increase further. Q_EC increases then due to structural recirculation. IVC inferior vena cava, PULM-Shunt pulmonary shunt, Q_EC extracorporeal pump flow, Q_Eff effective extracorporeal pump flow, Q_C cardiac output, RA right atrium, SaO₂ arterial blood oxygen saturation, S_PAO₂ pulmonary arterial blood oxygen saturation, “SvO₂” mixed venous blood oxygen saturation, SVC superior vena cava

Fig. 4

Required Q_EC to reach target SaO₂. IVC inferior vena cava, PULM-Shunt pulmonary shunt, Q_EC extracorporeal pump flow, Q_C cardiac output, RA right atrium, SaO₂ arterial blood oxygen saturation, SVC superior vena cava

Fig. 5

Reduction in required Q_EC from the IVC → RA route to the IVC + SVC → RA route. IVC inferior vena cava, PULM-Shunt pulmonary shunt, Q_EC extracorporeal pump flow, Q_C cardiac output, RA right atrium, SaO₂ arterial blood oxygen saturation, SVC superior vena cava

Fig. 6

Changing the configuration from VV ECMO to VV-V ECMO. After clamping the 2 initial cannulas, tubings can be cut in conserving some length. An Y-piece connector is then positioned to reunite these 2 tubings. This Y-piece is also connected to the drainage tubing of ECMO system. Oxygenator used in V-V configuration may be conserved or changed if its performance is too altered. All tubings must be totally purged of air before connection. A complementary tubing may be necessary on return line between ECMO system and returning cannula if oxygenator is conserved. Once totally purged of air, returning cannula may be connected to the ECMO system and VV-V extracorporeal circulation may be started. In our experience, the femoral/jugular couples (29Fr–55 cm)/(22Fr–15 cm) and (27Fr–61 cm)/(20Fr–15 cm) have good balance in term of drainage, with flow percentages frequently comprised between 60%/40% and 70%/30%, respectively