The Hemodynamic Burden of Femoral Extracorporeal Life Support for Severe Circulatory Failure: Investigating Competing Flow Phenomena with Color Doppler Sonography

 

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Objectives: Femoral extracorporeal life support systems (ECLS) during acute circulatory failure should provide hemodynamic stability and left ventricular unloading. Unfortunately, a retrograde flow in the aorta and a remaining pulmonary blood flow leads to increased left ventricular afterload and dilation. It may delay cardiac recovery and induce end organ malperfusion. Furthermore, the intricately connected flow interactions between ECLS and human circulation are poorly understood. Since these can't be investigated systematically in-vivo we investigated these flow interactions in the aorta and its branches in a newly developed flexible mock circulatory loop in vitro.

Methods: To mimic the circulatory system, we mounted two 1:1 silicon based vascular models (aorta, vena cava) with resistance and compliance elements in a water reservoir. Ventricular function was established with two paracorporeal assist devices, an ECLS system was connected through femoral access ports. Circulatory depression and recovery was simulated with four degrees of cardiac output (1, 2, 3 and 4 l/min) with four corresponding degrees of ECLS support (4, 3, 2 and 1 L/min). We investigated aortic blood flow velocity, blood flow and direction and possible mixing zones with 2D- and Doppler-ultrasound at 15 regions of interest in the aorta, supraaortic and visceral branches.

Results: During almost full ECLS support (3–4 L/min) the majority of the aorta was perfused with retrograde flow which didn't reach the supraaortic branches and ascending aorta. The opposing flows were separated at a distinct but narrow border zone at the aortic isthmus (1–1.5 cm) without extensive turbulent flow phenomena outside the zone. Even higher ECLS flows didn't shift the zone toward the aortic arch. In contrast reduced ECLS flow shifted the border zone toward the visceral region. Combined high ECLS flow and cardiac output (4 vs. 3 L/min) leads to nearly stagnant flow in the aorta.

Conclusion: Femoral ECLS support can restore hemodynamic stability but seems not capable of sufficiently providing perfusion to proximal organs, namely, the coronary arteries and the brain. Reduced blood flow velocities in the supraaortic and visceral branches and a commonly disturbed pulmonary gas exchange may lead to reduced oxygen delivery and thus delay cardiac recovery and markedly affect end organ function. Thus an early switch to a non-opposing but probably supporting subclavian access could be preferable.