Cannula Pairing Determines Distal Limb Perfusion During Peripheral Veno‐Arterial Extracorporeal Membrane Oxygenation: An Experimental Mock‐Loop Study

BACKGROUND: Limb ischaemia remains a common complication of peripheral venoarterial extracorporeal membrane oxygenation (VA-ECMO). Reinforced introducer sheaths are commonly used off-label as distal perfusion cannulas; however, their ability to provide adequate distal flow across clinically relevant ECMO configurations remains uncertain. We sought to evaluate the influence of cannula size configurations on distal flow fraction using a simple mock circulatory loop. METHODS: Distal flow fraction was evaluated across 24 configurations comprising 15-21Fr arterial return cannulas and 7-9Fr reinforced introducer sheaths. Direct and indirect connection of the DPC to the arterial return cannula was compared. Measurements were obtained at circuit flows from 1 to 5 L/min in 100 mL/min increments. RESULTS: Distal flow fraction significantly decreased with increasing arterial return cannula size (β = -0.796 percentage points; 95% CI, -0.844 to -0.748; p < 0.001), and indirect DPC connection (β = -0.475 percentage points; 95% CI, -0.588 to -0.362; p < 0.001). In comparison, increasing DPC size was overall associated with a small and insignificant augmentation of the distal flow fraction (β +0.098 percentage points per Fr; 95% CI -0.014 to +0.210; p = 0.087). At the lowest circuit flow (1 L/min), the maximum distal flow achieved by any configuration was 86 mL/min. CONCLUSIONS: In this controlled hydraulic experiment, larger arterial return cannulas reduced DPC flow relative to total circuit flow. Distal flow was particularly limited at low total circuit flows, potentially compromising limb perfusion during ECMO weaning. These findings support further investigation to evaluate the appropriateness of introducer sheath devices for the purposes of distal limb protection.