Purpose: Recirculation is a critical issue in veno-venous extracorporeal membrane oxygenation (VV ECMO). We propose a novel method for estimating the recirculation ratio using temporary sweep-gas control.

Methods: A circuit simulating VV ECMO recirculation was constructed by introducing a short circuit between the inlet and outlet of the oxygenator, enabling direct measurement of recirculation flow. Temporary cessation of sweep gas induced decreases in oxygen saturation at the oxygenator inlet (S_preO₂) and outlet (S_postO₂). The ratio of their temporal changes (⊿S_preO₂/⊿S_postO₂) converged to the recirculation ratio, reflecting blood mixing. The early prediction phase was defined as the interval required for oxygen saturation to decrease from 99% to 95% after sweep-gas cessation. The method was validated in an acute porcine model.

Results: In circuit experiments, the relative prediction error was 7.0% ± 5.2%. Early prediction required 3.0 ± 1.0 s when recirculation was ≤50% and 4.1 ± 1.0 s when >50%. In animal experiments, the error was 7.5% ± 4.0%, with times of 10.4 ± 2.8 s for recirculation ≤50% and 27.8 ± 0.5 s for >50%.

Conclusions: The proposed method enables rapid, less invasive prediction of the recirculation ratio and may provide a practical tool for optimizing ECMO management.