Association between controlled mechanical ventilation and systemic inflammation in acute hypoxemic respiratory failure: an observational cohort study

Critical Care volume 29, Article number: 482 (2025) Published: 11 November 2025

Background

In patients with acute hypoxemic respiratory failure, spontaneous breathing efforts may contribute to patient self-inflicted lung injury through increased ventilation inhomogeneity and systemic inflammation. Whether early transition to controlled mechanical ventilation (CMV) mitigates these effects remains uncertain.

Methods

This observational, prospective cohort study included 40 ICU patients with acute hypoxemic respiratory failure who initially breathed spontaneously. Based on clinical decisions, patients were managed with either continued spontaneous breathing (SB group, n = 12) or transitioned to CMV (CMV group, n = 28). Arterial blood gases, hemodynamics, plasma cytokines (IL-6 and IL-8), and ventilation distribution via electrical impedance tomography (EIT) were recorded at baseline and after 24 h. In the CMV group, intermediate time points (T2, T6, T12) were also assessed after intubation. The trial was registered in ClinicalTrials.gov (NCT03513809).

Results

In the CMV group, respiratory rate and heart rate decreased significantly over time. IL-6 levels dropped markedly from 305 ± 938 pg/mL at baseline to 27 ± 58 pg/mL at 24 h (p = 0.0195), accompanied by a significant improvement in oxygenation (PaO₂/FiO₂ from 140 ± 51 to 199 ± 67, p = 0.0004). EIT data showed improved ventilation distribution with increased end-expiratory lung impedance, decreased global inhomogeneity, and a shift in the center of ventilation toward dorsal regions. In contrast, the SB group showed no significant changes over 24 h in gas exchange, systemic inflammation, or EIT-derived parameters.

Conclusions

In patients with acute hypoxemic respiratory failure initially breathing spontaneously, transition to CMV was associated with reduced IL-6 levels and improved ventilatory homogeneity over 24 h. These exploratory findings indicate that connection to controlled mechanical ventilation was associated with reduced systemic inflammation, a relationship that warrants confirmation in larger prospective studies.

 

 

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

Critical Care volume 29, Article number: 195 Published: 16 May 2025

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.

 

Ventilation distribution during spontaneous breathing trials predicts liberation from mechanical ventilation: the VISION study

Critical Care 29, Article number: 11(2025)

Published: 07 January 2025

Background

Predicting complete liberation from mechanical ventilation (MV) is still challenging. Electrical impedance tomography (EIT) offers a non-invasive measure of regional ventilation distribution and could bring additional information.

Research question.

Whether the display of regional ventilation distribution during a Spontaneous Breathing Trial (SBT) could help at predicting early and successful liberation from MV.

Study design and methods

Patients were monitored with EIT during the SBT. The tidal image was divided into ventral and dorsal regions and displayed simultaneously. We explored the ventral-to-dorsal ventilation difference in percentage, and its association with clinical outcomes. Liberation success was defined pragmatically as passing SBT followed by extubation within 24 h without reintubation for 7 days. Failure included use of rescue therapy, reintubation within 7 days, tracheostomy, and not being extubated within 24 h after succesful SBT. A training cohort was used for discovery, followed by a validation cohort.

Results

Among a total of 98 patients analyzed, 85 passed SBT (87%), but rapid liberation success occurred only in 40; 13.5% of extubated patients required reintubation. From the first minutes to the entire SBT duration, the absolute ventral-to-dorsal difference was consistently smaller in liberation success compared to all subgroups of failure (p < 0.0001). An absolute difference at 5 min of SBT > 20% was associated with failure of liberation, with sensitivity and specificity of 71% and 78% and positive predictive value 81% in a validation cohort.

Conclusion

During SBT, a large ventral-to-dorsal difference in ventilation indicated by EIT may help to rapidly identify patients at risk of liberation failure.

 

Electric impedance tomography-guided PEEP titration reduces mechanical power in ARDS: a randomized crossover pilot trial

by Jose Victor Jimenez, Elizabeth Munroe, Andrew J. Weirauch, Kelly Fiorino, Christopher A. Culter, Kristine Nelson, Wassim W. Labaki, Philip J. Choi, Ivan Co, Theodore J. Standiford, Hallie C. Prescott and Robert C. Hyzy 

Critical Care volume 27, Article number: 21 Published: 17 January 2023

Background

In patients with acute respiratory distress syndrome undergoing mechanical ventilation, positive end-expiratory pressure (PEEP) can lead to recruitment or overdistension. Current strategies utilized for PEEP titration do not permit the distinction. Electric impedance tomography (EIT) detects and quantifies the presence of both collapse and overdistension. We investigated whether using EIT-guided PEEP titration leads to decreased mechanical power compared to high-PEEP/FiO2 tables.

Methods

A single-center, randomized crossover pilot trial comparing EIT-guided PEEP selection versus PEEP selection using the High-PEEP/FiO2 table in patients with moderate–severe acute respiratory distress syndrome. The primary outcome was the change in mechanical power after each PEEP selection strategy. Secondary outcomes included changes in the 4 × driving pressure + respiratory rate (4 ΔP, + RR index) index, driving pressure, plateau pressure, PaO2/FiO2 ratio, and static compliance.

Results

EIT was consistently associated with a decrease in mechanical power compared to PEEP/FiO2 tables (mean difference − 4.36 J/min, 95% CI − 6.7, − 1.95, p = 0.002) and led to lower values in the 4ΔP + RR index (− 11.42 J/min, 95% CI − 19.01, − 3.82, p = 0.007) mainly driven by a decrease in the elastic–dynamic power (− 1.61 J/min, − 2.99, − 0.22, p = 0.027). The elastic–static and resistive powers were unchanged. Similarly, EIT led to a statistically significant change in set PEEP (− 2 cmH2O, p = 0.046), driving pressure, (− 2.92 cmH2O, p = 0.003), peak pressure (− 6.25 cmH2O, p = 0.003), plateau pressure (− 4.53 cmH2O, p = 0.006), and static respiratory system compliance (+ 7.93 ml/cmH2O, p = 0.008).

Conclusions

In patients with moderate–severe acute respiratory distress syndrome, EIT-guided PEEP titration reduces mechanical power mainly through a reduction in elastic–dynamic power.

 

Imaging the acute respiratory distress syndrome: past, present and future

 

Intensive Care Medicine volume 48, pages 995–1008 (2022) Published: 14 July 2022

 

In patients with the acute respiratory distress syndrome (ARDS), lung imaging is a fundamental tool in the study of the morphological and mechanistic features of the lungs. Chest computed tomography studies led to major advances in the understanding of ARDS physiology. They allowed the in vivo study of the syndrome’s lung features in relation with its impact on respiratory physiology and physiology, but also explored the lungs’ response to mechanical ventilation, be it alveolar recruitment or ventilator-induced lung injuries. Coupled with positron emission tomography, morphological findings were put in relation with ventilation, perfusion or acute lung inflammation. Lung imaging has always been central in the care of patients with ARDS, with modern point-of-care tools such as electrical impedance tomography or lung ultrasounds guiding clinical reasoning beyond macro-respiratory mechanics. Finally, artificial intelligence and machine learning now assist imaging post-processing software, which allows real-time analysis of quantitative parameters that describe the syndrome’s complexity. This narrative review aims to draw a didactic and comprehensive picture of how modern imaging techniques improved our understanding of the syndrome, and have the potential to help the clinician guide ventilatory treatment and refine patient prognostication.

Unmatched ventilation and perfusion measured by electrical impedance tomography predicts the outcome of ARDS

 

Unmatched ventilation and perfusion measured by electrical impedance tomography predicts the outcome of ARDS

 

by Elena Spinelli, Michael Kircher, Birgit Stender, Irene Ottaviani, Maria C. Basile, Ines Marongiu, Giulia Colussi, Giacomo Grasselli, Antonio Pesenti and Tommaso Mauri 

 

Critical Care volume 25, Article number: 192 (2021)

 

Background

In acute respiratory distress syndrome (ARDS), non-ventilated perfused regions coexist with non-perfused ventilated regions within lungs. The number of unmatched regions might reflect ARDS severity and affect the risk of ventilation-induced lung injury. Despite pathophysiological relevance, unmatched ventilation and perfusion are not routinely assessed at the bedside. The aims of this study were to quantify unmatched ventilation and perfusion at the bedside by electrical impedance tomography (EIT) investigating their association with mortality in patients with ARDS and to explore the effects of positive end-expiratory pressure (PEEP) on unmatched ventilation and perfusion in subgroups of patients with different ARDS severity based on PaO2/FiO2 and compliance.

Methods

Prospective observational study in 50 patients with mild (36%), moderate (46%), and severe (18%) ARDS under clinical ventilation settings. EIT was applied to measure the regional distribution of ventilation and perfusion using central venous bolus of saline 5% during end-inspiratory pause. We defined unmatched units as the percentage of only ventilated units plus the percentage of only perfused units.

Results

Percentage of unmatched units was significantly higher in non-survivors compared to survivors (32[27–47]% vs. 21[17–27]%, p < 0.001). Percentage of unmatched units was an independent predictor of mortality (OR 1.22, 95% CI 1.07–1.39, p = 0.004) with an area under the ROC curve of 0.88 (95% CI 0.79–0.97, p < 0.001). The percentage of ventilation to the ventral region of the lung was higher than the percentage of ventilation to the dorsal region (32 [27–38]% vs. 18 [13–21]%, p < 0.001), while the opposite was true for perfusion (28 [22–38]% vs. 36 [32–44]%, p < 0.001).

Higher percentage of only perfused units was correlated with lower dorsal ventilation (r =  − 0.486, p < 0.001) and with lower PaO2/FiO2 ratio (r =  − 0.293, p = 0.039).

Conclusions

EIT allows bedside assessment of unmatched ventilation and perfusion in mechanically ventilated patients with ARDS. Measurement of unmatched units could identify patients at higher risk of death and could guide personalized treatment.