Calculation of Transpulmonary Pressure From Regional Ventilation Displayed by Electrical Impedance Tomography in Acute Respiratory Distress Syndrome

Past, present, and future of electrical impedance tomography and myography for medical applications: a scoping review

This scoping review summarizes two emerging electrical impedance technologies: electrical impedance myography (EIM) and electrical impedance tomography (EIT). These methods involve injecting a current into tissue and recording the response at different frequencies to understand tissue properties. The review discusses basic methods and trends, particularly the use of electrodes: EIM uses electrodes for either injection or recording, while EIT uses them for both. Ag/AgCl electrodes are prevalent, and current injection is preferred over voltage injection due to better resistance to electrode wear and impedance changes. Advances in digital processing and integrated circuits have shifted EIM and EIT toward digital acquisition, using voltage-controlled current sources (VCCSs) that support multiple frequencies. The review details powerful processing algorithms and reconstruction tools for EIT and EIM, examining their strengths and weaknesses. It also summarizes commercial devices and clinical applications: EIT is effective for detecting cancerous tissue and monitoring pulmonary issues, while EIM is used for neuromuscular disease detection and monitoring. The role of machine learning and deep learning in advancing diagnosis, treatment planning, and monitoring is highlighted. This review provides a roadmap for researchers on device evolution, algorithms, reconstruction tools, and datasets, offering clinicians and researchers information on commercial devices and clinical studies for effective use and innovative research.

The ventilator of the future: key principles and unmet needs

Persistent shortcomings of invasive positive pressure ventilation make it less than an ideal intervention. Over the course of more than seven decades, clinical experience and scientific investigation have helped define its range of hazards and limitations. Apart from compromised airway clearance and lower airway contamination imposed by endotracheal intubation, the primary hazards inherent to positive pressure ventilation may be considered in three broad categories: hemodynamic impairment, potential for ventilation-induced lung injury, and impairment of the respiratory muscle pump. To optimize care delivery, it is crucial for monitoring and machine outputs to integrate information with the potential to impact the underlying requirements of the patient and/or responses of the cardiopulmonary system to ventilatory interventions. Trending analysis, timely interventions, and closer communication with the caregiver would limit adverse clinical trajectories. Judging from the rapid progress of recent years, we are encouraged to think that insights from physiologic research and emerging technological capability may eventually address important aspects of current deficiencies.

Lung-Dependent Areas Collapse, Monitored by Electrical Impedance Tomography, May Predict the Oxygenation Response to Prone Ventilation in COVID-19 Acute Respiratory Distress Syndrome

OBJECTIVES

ICUs have had to deal with a large number of patients with acute respiratory distress syndrome COVID-19, a significant number of whom received prone ventilation, which is a substantial consumer of care time. The selection of patients that we have to ventilate in prone position seems interesting. We evaluate the correlation between the percentage of collapsed dependent lung areas in the supine position, monitoring by electrical impedance tomography and the oxygenation response (change in Pao2/Fio2 ratio) to prone position.

DESIGN

An observational prospective study.

SETTING

From October 21, 2020, to 30 March 30, 2021. At the Sainte Anne military teaching Hospital and the Timone University Hospital.

PATIENTS

Fifty consecutive patients admitted in our ICUs, with COVID-19 acute respiratory distress syndrome and required mechanical, were included. Twenty-four (48%) received prone ventilation. Fifty-eight prone sessions were investigated.

INTERVENTIONS

An electrical impedance tomography recording was made in supine position, daily and repeated just before and just after the prone session. The daily dependent area collapse was calculated in relation to the previous electrical impedance tomography recording. Prone ventilation response was defined as a Pao2/Fio2 ratio improvement greater than 20%.

MEASUREMENT AND MAIN RESULTS

The main outcome was the correlation between dependent area collapse and the oxygenation response to prone ventilation. Dependent area collapse was correlated with oxygenation response to prone ventilation (R2 = 0.49) and had a satisfactory prediction accuracy of prone response with an area under the curve of 0.94 (95% CI, 0.87-1.00; p < 0.001). Best Youden index was obtained for a dependent area collapse greater than 13.5 %. Sensitivity of 92% (95% CI, 78-97), a specificity of 91% (95% CI, 72-97), a positive predictive value of 94% (95% CI, 88-100), a negative predictive value of 87% (95% CI, 78-96), and a diagnostic accuracy of 91% (95% CI, 84-98).

CONCLUSIONS

Dependent lung areas collapse (> 13.5%), monitored by electrical impedance tomography, has an excellent positive predictive value (94%) of improved oxygenation during prone ventilation.

Time-Controlled Adaptive Ventilation Does Not Induce Hemodynamic Impairment in a Swine ARDS Model

Background

The current standard of care during severe acute respiratory distress syndrome (ARDS) is based on low tidal volume (VT) ventilation, at 6 mL/kg of predicted body weight. The time-controlled adaptive ventilation (TCAV) is an alternative strategy, based on specific settings of the airway pressure release ventilation (APRV) mode. Briefly, TCAV reduces lung injury, including: (1) an improvement in alveolar recruitment and homogeneity; (2) reduction in alveolar and alveolar duct micro-strain and stress-risers. TCAV can result in higher intra-thoracic pressures and thus impair hemodynamics resulting from heart-lung interactions. The objective of our study was to compare hemodynamics between TCAV and conventional protective ventilation in a porcine ARDS model.

Methods

In 10 pigs (63–73 kg), lung injury was induced by repeated bronchial saline lavages followed by 2 h of injurious ventilation. The animals were then randomized into two groups: (1) Conventional protective ventilation with a VT of 6 mL/kg and PEEP adjusted to a plateau pressure set between 28 and 30 cmH₂O; (2) TCAV group with P-high set between 27 and 29 cmH₂O, P-low at 0 cmH₂O, T-low adjusted to terminate at 75% of the expiratory flow peak, and T-high at 3–4 s, with I:E > 6:1.

Results

Both lung elastance and PaO₂:FiO₂ were consistent with severe ARDS after 2 h of injurious mechanical ventilation. There was no significant difference in systemic arterial blood pressure, pulmonary blood pressure or cardiac output between Conventional protective ventilation and TCAV. Levels of total PEEP were significantly higher in the TCAV group (p < 0.05). Driving pressure and lung elastance were significantly lower in the TCAV group (p < 0.05).

Conclusion

No hemodynamic adverse events were observed in the TCAV group compared as to the standard protective ventilation group in this swine ARDS model, and TCAV appeared to be beneficial to the respiratory system.

Lung aeration, ventilation, and perfusion imaging

PURPOSE OF REVIEW

Lung imaging is a cornerstone of the management of patients admitted to the intensive care unit (ICU), providing anatomical and functional information on the respiratory system function. The aim of this review is to provide an overview of mechanisms and applications of conventional and emerging lung imaging techniques in critically ill patients.

RECENT FINDINGS

Chest radiographs provide information on lung structure and have several limitations in the ICU setting; however, scoring systems can be used to stratify patient severity and predict clinical outcomes. Computed tomography (CT) is the gold standard for assessment of lung aeration but requires moving the patients to the CT facility. Dual-energy CT has been recently applied to simultaneous study of lung aeration and perfusion in patients with respiratory failure. Lung ultrasound has an established role in the routine bedside assessment of ICU patients, but has poor spatial resolution and largely relies on the analysis of artifacts. Electrical impedance tomography is an emerging technique capable of depicting ventilation and perfusion at the bedside and at the regional level.

SUMMARY

Clinicians should be confident with the technical aspects, indications, and limitations of each lung imaging technique to improve patient care.