Optimum electrical impedance tomography-based PEEP and recruitment-to-inflation ratio in patients with severe ARDS on venovenous ECMO
Alexandre Coppens, Sarah Aissi James, Hadrien Rozé, Charles Juvin, Benjamin Repusseau, Guillaume Lebreton, Charles‐Édouard Luyt, Guillaume Hékimian, Juliette Chommeloux, Marc Pineton de Chambrun, Alain Combes, Guillaume Franchineau, Matthieu Schmidt
Abstract
The significance of the Recruitment to Inflation (R/I) ratio in identifying PEEP recruiters in patients undergoing ultra-protective lung ventilation during venovenous ECMO is not well established. To compare the concordance of the R/I ratio and Electrical Impedance Tomography (EIT) in determining optimum PEEP settings in severe ARDS patients on ECMO and ventilated with very low tidal volumes. Initially, a low-flow insufflation was performed to detect and measure the airway opening pressure (AOP). Subsequently, the R/I ratio was calculated from PEEP 15–5 cmH2O, followed by a decremental PEEP trial (20–6 cmH2O in 2 cmH2O steps) monitored by EIT. The optimum EIT-based PEEP was defined as the intersection of the collapse and overdistension curves. Among 54 ECMO patients (tidal volume: 4.8 [3.0–6.0] mL/kg), 13 (24%) exhibited an airway opening pressure (AOP) of 11 (8–14) cmH2O. The cohort’s median R/I ratio was 0.43 (0.28–0.61). A tertile-based analysis of the R/I ratio (≤ 0.34; 0.34–0.54; > 0.54) revealed median optimum EIT-based PEEP of 8 [8–10], 10 [8–14], and 14 [12–16] cmH2O, respectively. The R/I ratio demonstrated weak inverse correlations with lung overdistension (R2 = 0.19) and positive correlations with lung collapse (R2 = 0.26) measured by EIT (p < 0.01). The R/I ratio is feasible during ultra-protective ventilation and provides valuable indications for guiding PEEP titration. Specifically, an R/I ratio > 0.34 may help identify patients likely to benefit from further individualized PEEP optimization using EIT. In contrast, when the R/I ratio is ≤ 0.34, a moderate PEEP level (8–10 cmH₂O) may suffice.