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. 2025 May 16;29(1):195.
doi: 10.1186/s13054-025-05437-0.

Optimum electrical impedance tomography-based PEEP and recruitment-to-inflation ratio in patients with severe ARDS on venovenous ECMO

Alexandre Coppens  1   2 , Sarah Aissi James  2 , Hadrien Roze  3   4 , Charles Juvin  1   5 , Benjamin Repusseau  4 , Guillaume Lebreton  1   5 , Charles-Edouard Luyt  1   2 , Guillaume Hékimian  1   2 , Juliette Chommeloux  1   2 , Marc Pineton de Chambrun  1   2 , Alain Combes  1   2 , Guillaume Franchineau  6 , Matthieu Schmidt  7   8
Affiliations

Optimum electrical impedance tomography-based PEEP and recruitment-to-inflation ratio in patients with severe ARDS on venovenous ECMO

Alexandre Coppens et al. Crit Care. .

Abstract

Rationale: 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.

Objectives: 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.

Methods: 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.

Main results: 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).

Conclusion: 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.

Keywords: Acute respiratory distress syndrome; Electrical impedance tomography; Extracorporeal membrane oxygenation; Recruitment-to-inflation ratio.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: Ethics approval was obtained from the appropriate legal and ethical authorities (CPP 2022-A02589-34). According to local legislation, signed informed consent was waived as the study reports data routinely acquired in usual care. Consent for publication: Not applicable. Competing interests: Alain Combes reports grants from Getinge, and personal fees from Getinge, Baxter, and Xenios outside the submitted work. Matthieu Schmidt reports lecture fees from Getinge, Dräger, Baxter, and Fresenius Medical Care outside the submitted work. The other authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
Study protocol with applied positive end-expiratory pressure (PEEP) steps. For further details, see the METHODS section. AOP, airway occlusion pressure; PEEP, Positive End Expiratory Pressure; Pplat, plateau pressure; VTEOLIA, tidal volume obtained with a driving pressure set at 14 cmH2O and a PEEP at 10 cmH2O in pressure-controlled ventilation; PCV, Pressure controlled ventilation; VCV, volume-controlled ventilation; R/I ratio, recruitment to inflation ratio
Fig. 2
Fig. 2
A Linear regression between overdistension estimated by EIT and recruitment to inflation ratio (n = 54) and B) collapse estimated by EIT and recruitment to inflation ratio (n = 41). Each dot represents one patient. The solid line represents the logistic regression fit, while the curved dashed lines indicate the 95% confidence interval. B Patients with an AOP were excluded from this analysis, as the collapse was not assessed below the level of the AOP
Fig. 3
Fig. 3
Distribution of the percentage of lung collapse (blue) and overdistension (red) during the decremental positive end-expiratory pressure (PEEP) trial for A Patients with a R/I ratio ≤ 0.34 (n = 18), B Patients with R/I ratio between 0.34 and 0.54 (n = 18), and C Patients with R/I ratio > 0.54 (n = 18). The internal horizontal line of the box plot is the median whereas the lower and upper box limits represent quartile 1 and quartile 3, respectively. Bars represent maximum/minimum
See this image and copyright information in PMC

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