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