Download - Electrical Impedance Tomography
Dr. med. Michael Czaplik
Electrical Impedance TomographyA path-breaking monitoring technique?
Dr. med. Michael Czaplik
My affiliations
Chair for Medical Information TechnologiesHelmholtz Institute for Biomedical Engineering
Department ofAnaesthesiologyUniversity 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
Birth of protective ventilation
ARDSnetwork. (2000) New Engl J Med 342:1301-8
Mor
talit
y
Tidal volume12ml 6ml
Dr. med. Michael Czaplik
Current ICU “concept”
Dr. med. Michael Czaplik
Individual variation
Non-responder
responder
Protective ventilation needs an individual tuning of ventilation pressures, especially of PEEP
Protective ventilation needs an individual tuning of ventilation pressures, especially of PEEP
Dr. med. Michael Czaplik
Role of CT imaging
Over-distended areas
Collapsed areas
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
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, …
• 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
• 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 measuresStatic or absolute EIT frames
Relative or dynamic sequences of EIT frames
Functional EIT images (fEIT)
1111
22
33
Time course of impedances44
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
Hinz J et al. Chest 2003; 123: 314-22.
Animal model, 12 pigs
ARDS induction with oleic acid
EIT compared to scintigraphy
Correlation coefficient (20 segments): 0,92 [0,86-0,97]
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
Tingay DG et al. Intensive Care Med. 2010; 36: 888-96.
Porcine animal model, ARDS induced by surfactant depletion
Comparison of two suction techniques
Effect depends on catheter diameter >> technique
Dr. med. Michael Czaplik
Clinical application: one-lung ventilation
Steinmann D et al. BJA 2008 Sep; 101: 411-8.
Clinical trial, 40 patients
Thorax surgery requiring one-lung ventilation
Correct placement of double-lumen tube was clearly visible
Dr. med. Michael Czaplik
Clinical application: one-lung ventilation
Pulletz S et al. Acta Anaesthesiol Scand. 2008; 52:1131-9.
Clinical trial, 10 patients
Thorax surgery requiring one-lung ventilation
Reliable detection necessitates ROI definition
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 non-invasive 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: 1596-1604.
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
Overlap of frequency bands
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
Quelle: Henning Lüpschen, "Automatisierte protektive Beatmung durch Bestimmung von Ventilation und Perfusion der Lunge mittels Elektrischer Impedanztomographie“, Shaker Verlag, 2012, to appear.
• 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
Separation of ventilation and perfusion IV
Pikkemaat, Leonhardt et al. Unpublished data
Dr. med. Michael Czaplik
Application of internal electrodesImage reconstruction
Perfusion/ventilation voltage ratio
conv tracheal oesoph
conv tracheal oesoph
Czaplik, Hoog-Antik et al. Unpublished data
Dr. med. Michael Czaplik
The future
Dr. med. Michael Czaplik
Thanks for your attention!
The future II