Objectives: Limb ischemia during extracorporeal life support (ECLS) using a femoral artery cannulation is frequently observed, also in patients with regular vessel diameters and without peripheral arterial occlusive disease. We investigated underlying pathomechanisms using an in silico fluid-mechanical simulation of the human circulation.
Methods: A life-sized model of the human heart, aorta and major vascular branches was virtualized using 3D segmentation software (Mimics, Materialise). Steady state simulation of different grades of cardiac output (0–100%) was simulated using Computational Fluid Dynamics (CFX, ANSYS). A straight cannula (virtualized 16 Fr. (5.3 mm) Cannula) was incorporated into the model via the left common femoral artery. ECLS flow varied between 1 and 5 L/min. The pressure boundary conditions at the arterial outlets were selected to demonstrate the downstream vascular system. Flow velocity and direction in various regions of the model was visualized.
Results: During all simulated stages of reduced cardiac output and consecutively adapted ECLS support, retrograde blood flow originating from the ECLS cannula was observed from the cannulation site up to the aortic bifurcation. ECLS flow never reached the ascending aorta. Despite a sufficiently large vessel diameter around the cannulation site (12mm), no antegrade flow into the distal femoral artery was present. Contrarily, retrograde flow from the distal limb, past the cannula toward the aortic bifurcation was observed. This effect can be explained by the Bernoulli principle, where the high-velocity retrograde ECLS-Jetstream induces areas of low pressure around the cannula with consecutive retrograde flow.
Conclusion: Even in patients with sufficient vessel diameters undergoing ECLS via femoral arterial cannulation, blood flow into the cannulated leg is impaired due to suction of blood from the limb by retrograde ECLS-flow. Thus, placement of a separate leg perfusion cannula is mandatory irrespective of vessel diameter or peripheral arterial occlusive disease.
