1 © Drägerwerk AG & Co. KGaA 1

Ventilation therapy involves numerous risks, and could lead to adverse effects. In addition, ventilation condition in the lungs can develop very differently over time in different regions. Traditional imaging procedures only provide a momentary picture of such conditions. Electrical impedance tomography (EIT), in contrast, enables dynamic visualization of the status of the lungs during ventilation. Although EIT has been in use in clinical settings since 2011, a few factors are still missing in order for it to become firmly established. However, the way to a new gold standard in intensive care and anesthesia has been initiated – and the current S3 guidelines on invasive ventilation also list EIT.

Electrical impedance tomography: On its way to gold standard?

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EIT ON ITS WAY TO GOLD STANDARD?

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Back in the 1980s, it was an impressive result: The first EIT devices delivered one image per second, provided they were used in the proper interference-free electromagnetic surroundings. Today after being part of everyday clinical routine for several years, EIT can provide a far more impressive total of 50 images per second. And external electromagnetic disturbances are much less of a hindrance in obtaining high-quality images of the lungs. EIT visualizes occurrences in the thorax using low-level alternating current in electrodes that rotate around the body. The electrodes are applied to the body surface and operate completely radiation-free.

Changes on the inside of the thorax result in changes in the electrical resistance and this can be determined through small voltage changes on the surface of the skin. To put it in a simplified way, an EIT image is a bioimpedance measurement of the body interior, mainly of the lungs. In contrast to other imaging modalities that work with ionizing radiation, EIT images have a lower spatial resolution but are highly dynamic1.

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Measurement of lung ventilation is the main applicationAlthough EIT was first invented as a medical process in the 1980s, it is still a relatively recent development. It has been used clinically since 2011 when the first EIT device was brought to the market. Up until now, the method has been used mainly for monitoring pulmonary function. Aside from the use of EIT for thoracic imaging, other new application possibilities are also being researched:

- Imaging of gastrointestinal function and evacuation - Visualization of certain cerebral functions- Early detection of breast cancer2

In addition to the dynamic imaging that it provides, EIT has other advantages as well: The examination is entirely without radiation and can be conducted at the patient‘s bedside. It allows for continuous monitoring of regional ventilation and thus a functional visualization of the lungs. Functional variables include:

- Regional compliance- Regional lung volume (e.g. tidal volumes)- Regional changes in end expiratory lung volume- Spatial and temporal ventilation variations1

This information can be used to detect signs of pulmonary hyper-distension or the collapse of individual pulmonary regions. No other imaging process provides comparable information directly at the patient‘s bedside and without any radiation exposure3.

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Current application and voltage measurements around the thorax with 16 electrodes.

Example of EIT generated image and dataPatient with Electrode Belt

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3 © Drägerwerk AG & Co. KGaA 3

Improved oxygenation and less tissue damageElectrical impedance tomography makes it possible to individually set different parameters in ventilation treatment so that equal ventilation distribution is ensured in the ventral and dorsal areas of the lungs. At the same time, this can reduce the stress the lung is exposed to. In the first prospective data on EIT-guided ventilation in connection with pulmonary injuries in an experimental setting, an improvement in gas exchange and respiratory mechanics was found with reduced histological evidence of ventilation-induced parenchymal lesions4. Scientists have been quick to recognize the substantial benefits offered by EIT in connection with early detection of regional impairments such as possible injuries pneumothorax or pulmonary edema.

Individual PEEP adjustment minimizing regional transpulmonary pressuresWith the measurement of esophageal pressure, the transpulmonary pressure rather than the absolute pressure can be assessed. As it is the transpulmonary pressure that the lung “sees”, it is the relevant pressure to avoid lung collapse on one hand and to avoid too high pressures and lung hyperdistension on the other. Unfortunately, measuring esophageal pressure is influenced by many variables and does not account for regional differences in transpulmonary pressures brought about by the hydrostatic gradient of the thorax or medistinal weight9. Also, heterogeneities of lung regions with adjacent areas of “solid-like” and “fluid-like” behavior, which are known to act as stress raisers, are not considered and may lead to under- or overestimation of the required PEEP setting10. In contrast to this, EIT can be used to visualize changes in regional compliances associated with collapse and hyperdistension at different PEEP levels. The caregiver can now see what happens at different PEEP steps and then chose the least injurious compromise of lung collapse and hyperdistension11.

Lung recruitment can be individually adapted and less harmfulIt is well known that recruitment maneuvers involve a risk of adverse barotraumatic, volutraumatic and hemodynamic effects5. EIT also provides benefits in handling this situation. When considering the countervailing options of restoring adequate oxygenation and protecting lung tissue as much as possible, EIT helps to achieve an exact setting of the necessary parameters. This makes it possible, for example, to adjust PEEP (Positive End Expiratory Pressure) at the patient‘s bedside. The precise evaluation of ventilation conditions using EIT thus facilitates personalized lung recruitment3.

Monitoring can be optimized with a combination of EIT and regular oxygenation measurements as shown in a prospective study conducted in 2016 (Yun et al.). In addition, it is possible to distinguish more quickly between patients who are responding to RMs and those who are not. In 20 test subjects, the difference in oxyge-nation prior to the RM and two minutes afterwards was analyzed

Define recruitability of a patient to personalize ventilation

Find the optimal PEEP with the help of a decremental PEEP trial?

using EIT and oxygen measurement. Only ten of those tested were actually responding6. This innovative approach thus facilitates the decision for or against a recruitment strategy in ARDS (Acute Respiratory Distress Syndrome) patients; it also supports a selection of ventilation parameters appropriate to the situation following successful recruitment (e.g. the subsequent PEEP). First promising results for setting PEEP based on EIT showed ventilation at lower driving pressures in the EIT group compared to patients who were ventilated according to the ARDS net protocol7. Nonetheless, further studies for optimization are indicated8.

responder non-responder

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Image-guided lung protection with Evita V500 and PulmoVista 500 • find a compromise to minimize VALI • adjust the ventilator settings accordingly    

Overdistension

Collapse

IMAGE-GUIDED LUNG PROTECTIONto treat the unseen

MECHANICAL VENTILATION IN INTENSIVE CARE

MECHANISMS OF VALI

PROTECT THE LUNG WITH PERSONALIZED VENTILATION

IMAGE-GUIDED LUNG PROTECTION

PULMOVISTA 500 HELPS TO REDUCE VILI7

PULMOVISTA 500 CAN IMPROVE VENTILATION WITH LOWER DRIVING PRESSURE8

PULMOVISTA 500 HELPS OPTIMIZE VENTILATION SETTINGS6

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Acute respiratory distress syndrome (ARDS) might be a consequence of ventilator associated lung injury (VALI) that should be prevented rather than treated.1

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responder non-responder

FACTS23% of all mechanically ventilatedpatients develop ARDS2

40% of all ARDS cases are not being diagnosed2

Mortality of ARDS is up to 45% depending on the severity of ARDS2

Almost 50% of ARDS survivors do not return to work one year after ICU discharge due to intensive care-acquired weakness3

LIMIT

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lung heterogeneity�

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regional stress and strain5

DIFFERENTIATE FIND

between responder and non-responder to a recruitment maneuver

personalized PEEP and Drivingpressure (ΔP)

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ATELECTRAUMAVOLU-/BAROTRAUMA

Tidal Recruitment(cyclic opening and closing)

InflammationBiotrauma

Evita InfinityV500

PulmoVista500

Multisystem OrganFailure (MSOF)

AlveolarOverdistension

Driving pressure

Pplat Plateau pressure4

Tidal Volume perpredicted body weight

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atelectasis

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regions of collapse close to open lung regions

PEEP trial with QuickSet / PressureLink –Evita® Infinity V500Conveniently change PEEP with constant driving pressure using only one knob

TURN THE KNOB AND PUSH THE BUTTON

Diagnostic View – PulmoVista 500

SEE THE UNSEEN

TREAT THE PREVIOUSLY UNSEEN AND FIND THE BALANCE

1) Villar and Slutsky, 'Is acute respiratory distress syndrome an iatrogenic disease?', Crit Care, Feb. 2010.

2) Bellani et al., ‘Epidemiology, Patterns of Care, and Mortality for Patients With Acute Respiratory Distress Syndrome in Intensive Care Units in 50 Countries’, JAMA, vol. 315, Feb. 2016.

3) Kamdar et al., ‘Joblessness and Lost Earnings after Acute Respiratory Distress Syndrome in a 1-Year National Multicenter Study.’, Am J Respir Crit Care Med., Oct. 2017.

4) Amato et al., ‘Driving Pressure and Survival in the Acute Respiratory Distress Syndrome’, N. Engl. J. Med., vol. 372, Feb. 2015.

5) Gattinoni et al., ‘Lung recruitment in patients with the acute respiratory distress syndrome’, N. Engl. J. Med., vol. 354, Apr. 2006.

6) Wolf et al., ‘Mechanical Ventilation Guided by Electrical Impedance Tomogra-phy in Experimental Acute Lung Injury’, Crit. Care Med., vol. 41, May 2013.

7) Kotani et al., ‘Electrical impedance tomography-guided prone positioning in a patient with acute cor pulmonale associated with severe acute respiratory distress syndrome’, J. Anesth., vol. 30, Feb. 2016.

8) Roldan et al., ‘PEEP Titration In Severe Acute Respiratory Distress Syndrome: Different Physiological Consequences When Guided By Electrical Impedance Tomography Versus Esophageal Pressure’, in B24. CRITICAL CARE: ACUTE RESPIRATORY FAILURE-MECHANICAL VENTILATION AND BEYOND, May 2017.

One-step or multi-step recruitment – Perseus® A500

Pinsp PEEP

Pinsp PEEP

PEEP

Pinsp

PEEPoptimal PEEP?

ΔP

What is lacking for recognition of EIT as a standard?The biggest obstacle for the recognition of EIT as a standard procedure has been and remains the absence of a definition of essential EIT parameters and their significance for immediate decisions in therapeutic situations. As with ultrasound, there is also a need for a standardized examination procedure. A concrete classification of measurement results and treatment recommendations and diagnoses still needs to be developed before it will be possible to speak of a new gold standard. Further large clinical studies first have to provide a standardized interpretation and presentation of results. The process of becoming part of the clinical routine has been underway some time now. It is increasingly recommended for ventilator management12

and according to Heines et al. “EIT […] is a promising tool which has a large potential for becoming the golden standard as a bedside patient-tailored ventilatory setting tool”13.

Schematic view of development of overdistension and collapse during a PEEP trial.

IMPRINTGERMANYDrägerwerk AG & Co. KGaAMoislinger Allee 53–5523542 Lübeck

www.draeger.com

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1. Kluge S et al., “DIVI Jahrbuch 2013/2014: Fortbildung und Wissenschaft in der interdisziplinären Intensivmedizin und Notfallmedizin”, Medizinisch-wissenschaftliche

Verlagsgesellschaft Berlin, 2014

2. Kaufmann S, “Instrumentierung der Bioimpedanzmessung: Optimierung mit Fokus auf die Elektroimpedanztomographie (EIT)“, Springer Fachmedien Wiesbaden, 2015

3. Marx G et al., “Die Intensivmedizin. 12. Auflage”, Springer-Verlag Berlin Heidelberg, 2015

4. Wolf GK et al., “Mechanical ventilation guided by electrical impedance tomography in experimental acute lung injury”, Crit Care Med., 2013

5. Strieben HW, ”Operative Intensivmedizin: Sicherheit in der klinischen Praxis”, Schattauer GmbH, 2008

6. Yun L et al., “Assessment of Lung Recruitment by Electrical Impedance Tomography and Oxygenation in ARDS Patients”, Medicine (Baltimore), 2016

7. Eronia N et al., ”Bedside selection of positive end-expiratory pressure by electrical impedance tomography in hypoxemic patients: a feasibility study“, Ann. Intensive Care, 2017.

8. Rosa RG et al., “Use of thoracic electrical impedance tomography as an auxiliary tool for alveolar recruitment maneuvers in acute respiratory distress syndrome: case

report and brief literature review”, Rev Bras Ter Intensiva, 2015

9. Sahetya SK and Brower RG, ”The promises and problems of transpulmonary pressure measurements in acute respiratory distress syndrome“, Curr. Opin. Crit. Care, 2016.

10. Yoshida T et al., ”Fifty Years of Research in ARDS. Spontaneous Breathing during Mechanical Ventilation. Risks, Mechanisms, and Management“, Am. J. Respir. Crit. Care Med., 2017.

11. Roldan R et al., ”PEEP Titration In Severe Acute Respiratory Distress Syndrome: Different Physiological Consequences When Guided By Electrical Impedance Tomography

Versus Esophageal Pressure”, Am J Respir Crit Care Med, 2017

12. Amado-Rodríguez L et al., ”Mechanical ventilation in acute respiratory distress syndrome:

The open lung revisited“, Med. Intensiva, 2017.

13. Heines SJH et al., ”Clinical implementation of electric impedance tomography in the treatment of ARDS:

a single centre experience“, J. Clin. Monit. Comput., 2018.

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