Electrical Impedance Tomography
A path-breaking monitoring technique?
Dr. med. Michael Czaplik
My affiliations
Chair for Medical Information
Technologies
Helmholtz Institute for
Biomedical Engineering
Department of
Anaesthesiology
University Hospital Aachen
Dr. med. Michael Czaplik
Outline
1. Do we need another monitoring technique?
2. How does Electrical Impedance Tomography
work?
3. Is there any evidence that EIT generates more
than colourful images?
4. Is EIT clinically established yet?
5. What will be in future?
Dr. med. Michael Czaplik
Do we need another
monitoring technique?
Dr. med. Michael Czaplik
Manoeuvring in respiratory treatment
Dr. med. Michael Czaplik
Mechanical ventilation in 2012
Dr. med. Michael Czaplik
Acute respiratory distress syndrome (ARDS)
 Acute onset
 Bilateral infiltrates
 Horowitz ratio (paO2/FiO2)
<300 / <200 / <100 mmHg
 Exclusion of a cardiac origin
Dr. med. Michael Czaplik
“Therapy” of ARDS
Dr. med. Michael Czaplik
Mortality
Birth of protective ventilation
12ml
6ml
Tidal volume
ARDSnetwork. (2000) New Engl J Med 342:1301-8
Dr. med. Michael Czaplik
Current ICU “concept”
FiO2 depends
on paO2
Respiratory
rate depends
on paCO2
Tidal volume
6 ml/kg BW
Dr. med. Michael Czaplik
PEEP
depends on
FiO2
Individual variation
 Protective ventilation needs an
individual tuning of ventilation
pressures, especially of PEEP
Non-responder
responder
Dr. med. Michael Czaplik
Role of CT imaging
Pro
precise anatomical information
Radiological density measure
1000 to -900 HU overdistended
-900 to -500 HU normal
-400 to -200 HU reduced ventilation
-100 to +100 HU atelectatic
Con
Overdistended
areas
Collapsed
areas
High level of radiation
No functional image
Not at the bedside
Dr. med. Michael Czaplik
How does Electrical
Impedance Tomography
work?
Dr. med. Michael Czaplik
Bioimpedance vs. biopotentials
• Internal electrical power sources
• Monitoring of internal ion currents flowing
through bio membranes
• Examples: ECG, EMG, EEG, …
• External electrical power sources
• Inject a small electrical AC current
• Evaluation of passive electrical properties
of all body tissues
• Examples: BIS, EIT
Dr. med. Michael Czaplik
Electrical impedance of biological tissue
Dr. med. Michael Czaplik
Principle of impedance tomography
Circular attachment of N electrodes (e.g. N=16)
Pairwise current injection (e.g. 5 mA at 50-200 kHz)
Voltage measurement between all remaining pairs
Recording of N x (N-3) voltages per frame (e.g. 208)
Dr. med. Michael Czaplik
Presentation of impedance measures
1
Static or absolute EIT frames
2
Relative or dynamic sequences of EIT frames
3
Functional EIT images (fEIT)
4
Time course of impedances
Dr. med. Michael Czaplik
Is there any evidence
that EIT generates more
than colourful images?
Dr. med. Michael Czaplik
Assessment of tidal volume
Dr. med. Michael Czaplik
Analysis of regional ventilation
Correlation of air content changes determined
by CT and impedance changes in 10 adult
patients during slow inflation.
Victorino et al. Am J Respir Crit Care Med 2004; 169: 791-800
Dr. med. Michael Czaplik
Analysis of regional ventilation II

Animal model, 12 pigs

ARDS induction with oleic acid

EIT compared to scintigraphy

Correlation coefficient (20 segments): 0,92 [0,86-0,97]
Hinz J et al. Chest 2003; 123: 314-22.
Dr. med. Michael Czaplik
Estimation of regional compliance

9 patients suffering from ARDS

Aim: Evaluation of regional ventilation regarding compliance

Successful recognition of breathes (96,0%; 97,6%)

Calculation of compliance: correlation coefficient of 0.8

Examination of regional ventilation under stepwise pressure increase
Gómez-Laberge C et al. IEEE Trans Med Imaging. 2012; 31: 834-42
Dr. med. Michael Czaplik
Monitoring of recruitment effects
Dr. med. Michael Czaplik
Clinical application: endotracheal suction

Porcine animal model, ARDS induced by
surfactant depletion

Comparison of two suction techniques

Effect depends on catheter diameter >> technique
Tingay DG et al. Intensive Care Med. 2010; 36: 888-96.
Dr. med. Michael Czaplik
Clinical application: one-lung ventilation

Clinical trial, 40 patients

Thorax surgery requiring one-lung ventilation

Correct placement of double-lumen tube was
clearly visible
Steinmann D et al. BJA 2008 Sep; 101: 411-8.
Dr. med. Michael Czaplik
Clinical application: one-lung ventilation

Clinical trial, 10 patients

Thorax surgery requiring one-lung ventilation

Reliable detection necessitates ROI definition
Pulletz S et al. Acta Anaesthesiol Scand. 2008; 52:1131-9.
Dr. med. Michael Czaplik
Clinical application: emergency medicine
Conclusion: EIT is an imaging modality for monitoring mechanical
ventilation during the relocation of patients. The application is noninvasive and without any exposure to radiation
Karmrodt J et al. Notfall & Rettungsmedizin 2004; 7:572–576
Dr. med. Michael Czaplik
Is EIT clinically
established yet?
Is there any evidence that EIT
improves clinical outcome?
Dr. med. Michael Czaplik
Dr. med. Michael Czaplik
Clinical trial examining outcome
Title: Strategies to Optimize Positive End-expiratory
Pressure (PEEP) in Patients With Acute Lung Injury
(EIT-PEEP) (University Hospital Bonn)
Primary Outcome Measures: homogeneity of regional
ventilation delay
Estimated enrollment: 40 patients
Estimated study completion: June 2013
Dr. med. Michael Czaplik
What will be in future?
Dr. med. Michael Czaplik
Clinical application: Monitoring of cerebral oedema
 Clinical trial, 200 healthy patients vs.
107 patients with cerebral infarction
 0,1mA @ 50kHz
 Usage of contralateral side as reference
 Aim: Monitoring of volume of cerebral oedema
with EIT compared to MRT or CT
 Accordance of about 75-85% (dependent on absolute volume)
He LY et al. Application of non-invasive cerebral electrical impedance
measurement on brain edema in patients with cerebral infarction. Neurol Res.
2010;32:770-4
Dr. med. Michael Czaplik
Clinical application: Cerebral haemorrhage
 Porcine animal model
 Blood injection to the cerebral frontal lobe
 Usage of contralateral side as reference
 16 electrodes attached to the head
 Calculation of mean impedance and relative changes in defined ROI
 High correlation with injected blood volume was achieved
Xu CH et al. Real-time imaging and detection of intracranial haemorrhage by
electrical impedance tomography in a piglet model. J. Int. Med. Res 2010; 38: 15961604.
Dr. med. Michael Czaplik
Cardiac related impedance changes

Clinical trial, 10 patients

Measurement of ventilation, perfusion and
ventilations-perfusions-ratio

Signal processing by band-pass filtering
Grant CA et al. Crit Care. 2011;15:R37.
Dr. med. Michael Czaplik
Separation of ventilation and perfusion I
Dr. med. Michael Czaplik
Separation of ventilation and perfusion II
Pikkemaat, Leonhardt et al. Unpublished data
Dr. med. Michael Czaplik
Separation of ventilation and perfusion III
Approach: using constrasting agents (10% NaCl)
Reference: SPECT / CT (99mTC labelled albumine)
Collaboration with Uppsala University (G. Hedenstierna)
4 healthy pigs (28-33 kg)
Volume-controlled ventilation
EIT device EEK2
Dr. med. Michael Czaplik
Separation of ventilation and perfusion IV
• NaCl-Bolus: 10 ml of 10 %
• First, NaCl-Bolus reaches the right
heart
• Then, high NaCl-concentration is
flowing to the lungs
• Finally, bolus reaches the left heart
 The impedance curves show curves
similiar to thermodilution
• Regional separation of the signal
according to the physiology seems
possible
Quelle: Henning Lüpschen, "Automatisierte protektive Beatmung durch Bestimmung von Ventilation
und Perfusion der Lunge mittels Elektrischer Impedanztomographie“,
Shaker Verlag, 2012, to appear.
Pikkemaat, Leonhardt et al. Unpublished data
Dr. med. Michael Czaplik
Application of internal electrodes
Image reconstruction
conv
tracheal
oesoph
Perfusion/ventilation voltage ratio
conv
tracheal
oesoph
Czaplik, Hoog-Antik et al. Unpublished data
Dr. med. Michael Czaplik
The future
Clinical establishment
V/Q-Mapping
Contactless measurement
3D-reconstruction
Measurement of abs. impedance
Multifrequency EIT
Higher resolution
Flexible electrode configuration
Dr. med. Michael Czaplik
The future II
Thanks for your attention!
Dr. med. Michael Czaplik