Cannula tip separation and configuration as determinants of recirculation in venovenous ECMO.

BACKGROUND: Recirculation during venovenous extracorporeal membrane oxygenation (VV ECMO) is an important phenomenon that limits the efficiency of support. Femoro-jugular (FJ) cannulation may be associated with lower recirculation than femoro-femoral (FF) configurations. Local practice is to routinely overlap cannula in the FJ configuration; this approach remains poorly described, and its impact on recirculation is not understood. METHODS: The saturation-based formula was used to assess recirculation fraction amongst 24 patients receiving VV ECMO between July 2018 and March 2025 in this single-centre retrospective study. All received VV ECMO via a multistage drainage cannula and a single-stage return. Factors considered relevant to recirculation were also collected at the time of a recirculation assessment, and cannula separation was obtained from chest X-ray imaging. Recirculation was compared between configurations, with further analysis where an overlap of cannula was present. Univariate and multivariate regression were performed to evaluate the influence on recirculation and clinical outcomes. RESULTS: Demography was similar between configurations, with the majority of VV ECMO indications being ARDS secondary to bacterial pneumonia. Patients in whom recirculation was assessable were similar to those excluded. Recirculation was non significantly lower amongst patients with FJ cannulation and lacked a clear relationship to extracorporeal blood flow and drainage tip position. There were no significant differences in clinical outcomes between cannula configurations, numerically higher rates of tracheostomy and awake ECMO were observed for FJ cannulations. Older age and higher vasoactive burden were associated with length of stay and survival. CONCLUSION: There are a dearth of studies investigating recirculation in patients with deliberate overlap of femoral and jugular cannula, particularly in the context of large calibre multistage drainage devices. A prospective study is necessary to systematically evaluate the influence of this practice on VV ECMO efficiency, ideally using advanced recirculation measurements and contemporaneous cardiac output monitoring.