The global inhomogeneity index assessed by electrical impedance tomography overestimates PEEP requirement in patients with ARDS: an observational study

Physiological definition for region of interest selection in electrical impedance tomography data: description and validation of a novel method

Objective. Geometrical region of interest (ROI) selection in electrical impedance tomography (EIT) monitoring may lack sensitivity to subtle changes in ventilation distribution. Therefore, we demonstrate a new physiological method for ROI definition. This is relevant when using ROIs to compute subsequent EIT-parameters, such as the ventral-to-dorsal ratio during a positive end-expiratory pressure (PEEP) trial.Approach.Our physiological approach divides an EIT image to ensure exactly 50% tidal impedance variation in the ventral and dorsal region. To demonstrate the effects of our new method, EIT measurements during a decremental PEEP trial in 49 mechanically ventilated ICU-patients were used. We compared the center of ventilation (CoV), a robust parameter for changes in ventro-dorsal ventilation distribution, to our physiological ROI selection method and different commonly used ROI selection methods. Moreover, we determined the impact of different ROI selection methods on the PEEP level corresponding to a ventral-to-dorsal ratio closest to 1.Main results.The division line separating the ventral and dorsal ROI was closer to the CoV for our new physiological method for ROI selection compared to geometrical ROI definition. Moreover, the PEEP level corresponding to a ventral-to-dorsal ratio of 1 is strongly influenced by the chosen ROI selection method, which could have a profound clinical impact; the within-subject range of PEEP level was 6.2 cmH2O depending on the chosen ROI selection method.Significance.Our novel physiological method for ROI definition is sensitive to subtle ventilation-induced changes in regional impedance (i.e. due to (de)recruitment) during mechanical ventilation, similar to the CoV.

The influence of different spontaneous breathing trials on regional ventilation distribution in patients with prolonged mechanical ventilation

OBJECTIVE

This study aimed to explore the influence of different spontaneous breathing trials (SBTs) on regional ventilation distribution in patients with prolonged mechanical ventilation (PMV).

METHODS

A total of 24 patients with PMV were analyzed retrospectively. They received three different SBT modes which are automatic tube compensation (ATC), continuous positive airway pressure (CPAP), and T-piece (TP), over three days, and every SBT lasted two hours. Electrical impedance tomography (EIT) was used to monitor the SBT process and five-minute EIT data from five periods (pre-SBT which is t0, at the beginning and the end of the first hour SBT are t1 and t2, at the beginning and the end of the second hour SBT are t3 and t4) were analyzed.

RESULTS

In all PMV patients, the temporal skew of aeration (TSA) values at t3 were significantly different in three SBTs (ATC: 18.18±22.97; CPAP: 20.42±17.01; TP:11.26±11.79; p=0.05). In the weaning success group, TSA (t1) values were significantly different too (ATC: 11.11±13.88; CPAP: 19.09±15.77; TP: 9.09±12.74; p=0.04). In the weaning failure group, TSA (t4) values were significantly different in three SBTs (ATC: 36.67±18.46; CPAP: 15.38±11.69; TP: 17.65±17.93; p=0.04). The patient's inspiratory effort (Global flow index at t1) in patients with weaning failure under CPAP (3.51±4.31) was significantly higher than that in the ATC (1.15±1.47) and TP (0.89±1.28). The SBT mode with the best ventilation uniformity may be the one that activates the respiratory muscles the most which may be the optimal SBT. The SBT mode of most uniform ventilation distribution settings varies from patient to patient.

CONCLUSION

The regional ventilation distribution was different for each individual, making the SBT with the best ventilation distribution of patients need to be personalized. EIT is a tool that can be considered for real-time assessment.

Contribution of electrical impedance tomography to personalize positive end-expiratory pressure under ECCO2R

Extracorporeal Carbon Dioxide Removal (ECCO2R) is used in acute respiratory distress syndrome (ARDS) patients to facilitate lung-protective ventilatory strategies. Electrical Impedance Tomography (EIT) allows individual, non-invasive, real-time, bedside, radiation-free imaging of the lungs, providing global and regional dynamic lung analyses. To provide new insights for future ECCO2R research in ARDS, we propose a potential application of EIT to personalize End-Expiratory Pressure (PEEP) following each reduction in tidal volume (VT), as demonstrated in an illustrative case. A 72-year-old male with COVID-19 was admitted to the ICU for moderate ARDS. Monitoring with EIT was started to determine the optimal PEEP value (PEEPEIT), defined as the intersection of the collapse and overdistention curves, after each reduction in VT during ECCO2R. The identified PEEPEIT values were notably low (< 10 cmH2O). The decrease in VT associated with PEEPEIT levels resulted in improved lung compliance, reduced driving pressure and a more uniform ventilation pattern. Despite current Randomized Controlled Trials showing that ultra-protective ventilation with ECCO2R does not improve survival, the applicability of universal ultra-protective ventilation settings for all patients remains a subject of debate. Inappropriately set PEEP levels can lead to alveolar collapse or overdistension, potentially negating the benefits of VT reduction. EIT facilitates real-time monitoring of derecruitment associated with VT reduction, guiding physicians in determining the optimal PEEP value after each decrease in tidal volume. This original description of using EIT under ECCO2R to adjust PEEP at a level compromising between recruitability and overdistention could be a crucial element for future research on ECCO2R.

Flow-controlled ventilation decreases mechanical power in postoperative ICU patients

BACKGROUND

Mechanical power (MP) is the energy delivered by the ventilator to the respiratory system and combines factors related to the development of ventilator-induced lung injury (VILI). Flow-controlled ventilation (FCV) is a new ventilation mode using a constant low flow during both inspiration and expiration, which is hypothesized to lower the MP and to improve ventilation homogeneity. Data demonstrating these effects are scarce, since previous studies comparing FCV with conventional controlled ventilation modes in ICU patients suffer from important methodological concerns.

OBJECTIVES

This study aims to assess the difference in MP between FCV and pressure-controlled ventilation (PCV). Secondary aims were to explore the effect of FCV in terms of minute volume, ventilation distribution and homogeneity, and gas exchange.

METHODS

This is a physiological study in post-cardiothoracic surgery patients requiring mechanical ventilation in the ICU. During PCV at baseline and 90 min of FCV, intratracheal pressure, airway flow and electrical impedance tomography (EIT) were measured continuously, and hemodynamics and venous and arterial blood gases were obtained repeatedly. Pressure-volume loops were constructed for the calculation of the MP.

RESULTS

In 10 patients, optimized FCV versus PCV resulted in a lower MP (7.7 vs. 11.0 J/min; p = 0.004). Although FCV did not increase overall ventilation homogeneity, it did lead to an improved ventilation of the dependent lung regions. A stable gas exchange at lower minute volumes was obtained.

CONCLUSIONS

FCV resulted in a lower MP and improved ventilation of the dependent lung regions in post-cardiothoracic surgery patients on the ICU. Trial registration Clinicaltrials.gov identifier: NCT05644418. Registered 1 December 2022, retrospectively registered.

Setting positive end-expiratory pressure by using electrical impedance tomography

PURPOSE OF REVIEW

This review presents the principles and possibilities of setting positive end-expiratory pressure (PEEP) using electrical impedance tomography (EIT). It summarizes the major findings of recent studies where EIT was applied to monitor the effects of PEEP on regional lung function and to guide the selection of individualized PEEP setting.

RECENT FINDINGS

The most frequent approach of utilizing EIT for the assessment of PEEP effects and the PEEP setting during the time period from January 2022 till June 2023 was based on the analysis of pixel tidal impedance variation, typically acquired during stepwise incremental and/or decremental PEEP variation. The most common EIT parameters were the fraction of ventilation in various regions of interest, global inhomogeneity index, center of ventilation, silent spaces, and regional compliance of the respiratory system. The studies focused mainly on the spatial and less on the temporal distribution of ventilation. Contrast-enhanced EIT was applied in a few studies for the estimation of ventilation/perfusion matching.

SUMMARY

The availability of commercial EIT devices resulted in an increase in clinical studies using this bedside imaging technology in neonatal, pediatric and adult critically ill patients. The clinical interest in EIT became evident but the potential of this method in clinical decision-making still needs to be fully exploited.

Regional ventilation distribution before and after laparoscopic lung parenchymal resection

Objective.The aim of the present study was to evaluate the influence of one-sided pulmonary nodule and tumour on ventilation distribution pre- and post- partial lung resection.Approach.A total of 40 consecutive patients scheduled for laparoscopic lung parenchymal resection were included. Ventilation distribution was measured with electrical impedance tomography (EIT) in supine and surgery lateral positions 72 h before surgery (T1) and 48 h after extubation (T2). Left lung to global ventilation ratio (Fl), the global inhomogeneity index (GI), standard deviation of regional ventilation delay (RVDSD) and pendelluft amplitude (Apendelluft) were calculated to assess the spatial and temporal ventilation distribution.Main results.After surgery (T2), ventilation at the operated chest sides generally deteriorated compared to T1 as expected. For right-side resection, the differences were significant at both supine and left lateral positions (p< 0.001). The change of RVDSDwas in general more heterogeneous. For left-side resection, RVDSDwas worse at T2 compared to T1 at left lateral position (p= 0.002). The other EIT-based parameters showed no significant differences between the two time points. No significant differences were observed between supine and lateral positions for the same time points respectively.Significance.In the present study, we found that the surgery side influenced the ventilation distribution. When the resection was performed on the right lung, the postoperative ipsilateral ventilation was reduced and the right lung ratio fell significantly. When the resection was on the left lung, the ventilation delay was significantly increased.

Clinical Applicability of Electrical Impedance Tomography in Patient-Tailored Ventilation: A Narrative Review

Electrical Impedance Tomography (EIT) is a non-invasive bedside imaging technique that provides real-time lung ventilation information on critically ill patients. EIT can potentially become a valuable tool for optimising mechanical ventilation, especially in patients with acute respiratory distress syndrome (ARDS). In addition, EIT has been shown to improve the understanding of ventilation distribution and lung aeration, which can help tailor ventilatory strategies according to patient needs. Evidence from critically ill patients shows that EIT can reduce the duration of mechanical ventilation and prevent lung injury due to overdistension or collapse. EIT can also identify the presence of lung collapse or recruitment during a recruitment manoeuvre, which may guide further therapy. Despite its potential benefits, EIT has not yet been widely used in clinical practice. This may, in part, be due to the challenges associated with its implementation, including the need for specialised equipment and trained personnel and further validation of its usefulness in clinical settings. Nevertheless, ongoing research focuses on improving mechanical ventilation and clinical outcomes in critically ill patients.

Benefits of secretion clearance with high frequency percussive ventilation in tracheostomized critically ill patients: a pilot study

Clearance of secretions remains a challenge in ventilated patients. Despite high-frequency percussive ventilation (HFPV) showing benefits in patients with cystic fibrosis and neuromuscular disorders, very little is known about its effects on other patient categories. Therefore, we designed a physiological pilot study investigating the effects on lung aeration and gas exchange of short HFPV cycles in tracheostomized patients undergoing mechanical ventilation. Electrical impedance tomography (EIT) was recorded at baseline (T0) by a belt wrapped around the patient's chest, followed by the HFPV cycle lasting 10 min. EIT data was collected again after the HFPV cycle (T1) as well as after 1 h (T2) and 3 h (T3) from T0. Variation from baseline of end-expiratory lung impedance (∆EELI), tidal variation (TIV) and global inhomogeneity index (GI) were computed. Arterial blood was also taken for gas analysis. HFPV cycle significantly improved the ∆EELI at T1, T2 and T3 when compared to baseline (p < 0.05 for all comparisons). The ratio between arterial partial pressure and inspired fraction of oxygen (PaO₂/FiO₂) also increased after the treatment (p < 0.001 for all comparison) whereas TIV (p = 0.132) and GI (p = 0.114) remained unchanged. Short cycles of HFPV superimposed to mechanical ventilation promoted alveolar recruitment, as suggested by improved ∆EELI, and improved oxygenation in tracheostomized patients with high load of secretion.Trial Registration Prospectively registered on www.clinicaltrials.gov (NCT05200507; dated 6th January 2022).