Inéz Frerichs

Electrical impedance tomography (EIT) in applications related to lung and ventilation: a review of experimental and clinical activities.

This review article is a summary of the publications dealing with the pulmonary applications of electrical impedance tomography (EIT). Original papers on EIT lung imaging published over 15 years are analysed and several aspects of the performed EIT measurements summarized. Information on the type of the EIT device and electrodes used, the studied transverse thoracic planes, the data acquisition rate, the number of studied animals, normal subjects or patients, the kind of lung pathology, the performed ventilatory manoeuvres and other interventions, as well as the applied reference techniques, is given. The type of the generated pulmonary EIT images and the quantitative analysis of the EIT data are described. Finally, the major results achieved are presented, followed by an analysis of the perspectives of EIT in clinical applications. A comparative analysis of the EIT hardware and the quality of the evaluation tools was not performed.

GREIT: A unified approach to 2D linear EIT reconstruction of lung images

Electrical impedance tomography (EIT) is an attractive method for clinically monitoring patients during mechanical ventilation, because it can provide a non-invasive continuous image of pulmonary impedance which indicates the distribution of ventilation. However, most clinical and physiological research in lung EIT is done using older and proprietary algorithms; this is an obstacle to interpretation of EIT images because the reconstructed images are not well characterized. To address this issue, we develop a consensus linear reconstruction algorithm for lung EIT, called GREIT (Graz consensus Reconstruction algorithm for EIT). This paper describes the unified approach to linear image reconstruction developed for GREIT. The framework for the linear reconstruction algorithm consists of (1) detailed finite element models of a representative adult and neonatal thorax, (2) consensus on the performance figures of merit for EIT image reconstruction and (3) a systematic approach to optimize a linear reconstruction matrix to desired performance measures. Consensus figures of merit, in order of importance, are (a) uniform amplitude response, (b) small and uniform position error, (c) small ringing artefacts, (d) uniform resolution, (e) limited shape deformation and (f) high resolution. Such figures of merit must be attained while maintaining small noise amplification and small sensitivity to electrode and boundary movement. This approach represents the consensus of a large and representative group of experts in EIT algorithm design and clinical applications for pulmonary monitoring. All software and data to implement and test the algorithm have been made available under an open source license which allows free research and commercial use.

Electrical impedance tomography: a method for monitoring regional lung aeration and tidal volume distribution?

ObjectiveTo demonstrate the monitoring capacity of modern electrical impedance tomography (EIT) as an indicator of regional lung aeration and tidal volume distribution.Design and settingShort-term ventilation experiment in an animal research laboratory.Patients and participantsOne newborn piglet (body weight: 2 kg).InterventionsSurfactant depletion by repeated bronchoalveolar lavage, surfactant administration.Measurements and resultsEIT scanning was performed at an acquisition rate of 13 images/s during two ventilatory manoeuvres performed before and after surfactant administration. During the scanning periods of 120 s the piglet was ventilated with a tidal volume of 10 ml/kg at positive end-expiratory pressures (PEEP) in the range of 0–30 cmH2O, increasing and decreasing in 5 cmH2O steps. Local changes in aeration and ventilation with PEEP were visualised by EIT scans showing the regional shifts in end-expiratory lung volume and distribution of tidal volume, respectively. In selected regions of interest EIT clearly identified the changes in local aeration and tidal volume distribution over time and after surfactant treatment as well as the differences between stepwise inflation and deflation.ConclusionsOur data indicate that modern EIT devices provide an assessment of regional lung aeration and tidal volume and allow evaluation of immediate effects of a change in ventilation or other therapeutic intervention. Future use of EIT in a clinical setting is expected to optimise the selection of appropriate ventilation strategies.

Regional lung perfusion as determined by electrical impedance tomography in comparison with electron beam CT imaging

The aim of the experiments was to check the feasibility of pulmonary perfusion imaging by functional electrical impedance tomography (EIT) and to compare the EIT findings with electron beam computed tomography (EBCT) scans. In three pigs, a Swan-Ganz catheter was positioned in a pulmonary artery branch and hypertonic saline solution or a radiographic contrast agent were administered as boli through the distal or proximal openings of the catheter. During the administration through the proximal opening, the balloon at the tip of the catheter was either deflated or inflated. The latter case represented a perfusion defect. The series of EIT scans of the momentary distribution of electrical impedance within the chest were obtained during each saline bolus administration at a rate of 13/s. EBCT scans were acquired at a rate of 3.3/s during bolus administrations of the radiopaque contrast material under the same steady-state conditions. The EIT data were used to generate local time-impedance curves and functional EIT images showing the perfusion of a small lung region, both lungs with a perfusion defect and complete both lungs during bolus administration through the distal and proximal catheter opening with an inflated or deflated balloon, respectively. The results indicate that EIT imaging of lung perfusion is feasible when an electrical impedance contrast agent is used.

Thoracic electrical impedance tomographic measurements during volume controlled ventilation-effects of tidal volume and positive end-expiratory pressure

The aim of the study was to analyze thoracic electrical impedance tomographic (EIT) measurements accomplished under conditions comparable with clinical situations during artificial ventilation. Multiple EIT measurements were performed in pigs in three transverse thoracic planes during the volume controlled mode of mechanical ventilation at various tidal volumes (V/sub T/) and positive end-expiratory pressures (PEEP). The protocol comprised following ventilatory patterns: (1) V/sub T/ (400, 500, 600, 700 ml) was varied in a random order at various constant PEEP levels and (2) PEEP (2, 5, 8, 11, 14 cm H/sub 2/O) was randomly modified during ventilation with a constant V/sub T/. The EIT technique was used to generate cross-sectional images of (1) regional lung ventilation and (2) regional shifts in lung volume with PEEP. The quantitative analysis was performed in terms of the tidal amplitude of the impedance change, reflecting the volume of delivered gas at various preset V/sub T/ and the end-expiratory impedance change, revealing the variation of the lung volume at various PEEP levels. The results showed: (1) an increase in the tidal amplitude of the impedance change, proportional to the delivered V/sub T/ at all constant PEEP levels, (2) a rising end-expiratory impedance change, with PEEP reflecting an increase in gas volume, and (3) a PEEP-dependent redistribution of the ventilated gas between the planes. The generated images and the quantitative results indicate the ability of EIT to identify regional changes in V/sub T/ and lung volume during mechanical ventilation.

Comparison of different methods to define regions of interest for evaluation of regional lung ventilation by EIT.

The measurement of regional lung ventilation by electrical impedance tomography (EIT) has been evaluated in many experimental studies. However, EIT is not routinely used in a clinical setting, which is attributable to the fact that a convenient concept for how to quantify the EIT data is missing. The definition of region of interest (ROI) is an essential point in the data analysis. To date, there are only limited data available on the different approaches to ROI definition to evaluate regional lung ventilation by EIT. For this survey we examined ten patients (mean age +/- SD: 60 +/- 10 years) under controlled ventilation. Regional tidal volumes were quantified as pixel values of inspiratory-to-expiratory impedance differences and four types of ROIs were subsequently applied. The definition of ROI contours was based on the calculation of the pixel values of (1) standard deviation from each pixel set of impedance data and (2) the regression coefficient from linear regression equations between the individual local (pixel) and average (whole scan) impedance signals. Additionally, arbitrary ROIs (four quadrants and four anteroposterior segments of equal height) were used. Our results indicate that both approaches to ROI definition using statistical parameters are suitable when impedance signals with high sensitivity to ventilation-related phenomena are to be analyzed. The definition of the ROI contour as 20-35% of the maximum standard deviation or regression coefficient is recommended. Simple segmental ROIs are less convenient because of the low ventilation-related signal component in the dorsal region.

Current practice in nutritional support and its association with mortality in septic patients--results from a national, prospective, multicenter study.

Objective:To identify current clinical practice regarding nutrition and its association with morbidity and mortality in patients with severe sepsis or septic shock in Germany. Design:Nationwide prospective, observational, cross-sectional, 1-day point-prevalence study. Setting:The study included 454 intensive care units from a representative sample of 310 hospitals stratified by size. Patients:Participants were 415 patients with severe sepsis or septic shock (according to criteria of the American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference). Interventions:None. Measurements and Main Results:Data were collected by on-site audits of trained external study physicians during randomly scheduled visits during 1 yr. Valid data on nutrition were available for 399 of 415 patients. The data showed that 20.1% of patients received exclusively enteral nutrition, 35.1% exclusively parenteral nutrition, and 34.6% mixed nutrition (parenteral and enteral); 10.3% were not fed at all. Patients with gastrointestinal/intra-abdominal infection, pancreatitis or neoplasm of the gastrointestinal tract, mechanical ventilation, or septic shock were less likely to receive exclusively enteral nutrition. Median Acute Physiology and Chronic Health Evaluation II and Sepsis-related Organ Failure Assessment scores were significantly different among the nutrition groups. Overall hospital mortality was 55.2%. Hospital mortality was significantly higher in patients receiving exclusively parenteral (62.3%) or mixed nutrition (57.1%) than in patients with exclusively enteral nutrition (38.9%) (p = .005). After adjustment for patient morbidity (Acute Physiology and Chronic Health Evaluation II score, presence of septic shock) and treatment factors (mechanical ventilation), multivariate analysis revealed that the presence of parenteral nutrition was significantly predictive of mortality (odds ratio, 2.09; 95% confidence interval, 1.29–3.37). Conclusions:Patients with severe sepsis or septic shock in German intensive care units received preferentially parenteral or mixed nutrition. The use of parenteral nutrition was associated with an increased risk of death.

Electrical impedance tomography in monitoring experimental lung injury

ObjectiveTo apply electrical impedance tomography (EIT) and the new evaluation approach (the functional EIT) in monitoring the development of artificial lung injury.DesignAcute experimental trial.SettingOperating room for animal experimental studies at a university hospital.SubjectsFive pigs (41.3 ± 4.1 kg, mean body weight ± SD).InterventionsThe animals were anaesthetised and mechanically ventilated. Sixteen electrodes were attached on the thoracic circumference and used for electrical current injection and surface voltage measurement. Oleic acid was applied sequentially (total dose 0.05 ml/kg body weight) into the left pulmonary artery to produce selective unilateral lung injury.Measurements and resultsThe presence of lung injury was documented by significant changes of PaCO2 (40.1 mmHg vs control 37.1 mmHg), PaO2 (112.3 mmHg vs 187.5 mmHg), pH (7.35 vs 7.42), mean pulmonary arterial pressure (29.2 mmHg vs 20.8 mmHg) and chest radiography. EIT detected 1) a regional decrease in mean impedance variation over the affected left lung (−41.4% vs control) and an increase over the intact right lung (+ 20.4 % vs control) indicating reduced ventilation of the affected, and a compensatory augmented ventilation of the unaffected lung and 2) a pronounced fall in local baseline electrical impedance over the injured lung (−20.6 % vs control) with a moderate fall over the intact lung (−10.0% vs control) indicating the development of lung oedema in the injured lung with a probable atelectasis formation in the contralateral one.ConclusionThe development of the local impairment of pulmonary ventilation and the formation of lung oedema could be followed by EIT in an experimental model of lung injury. This technique may become a useful tool for monitoring local pulmonary ventilation in intensive care patients suffering from pulmonary disorders associated with regionally reduced ventilation, fluid accumulation and/or cell membrane changes.

Monitoring perioperative changes in distribution of pulmonary ventilation by functional electrical impedance tomography

Background: Electrical impedance tomography (EIT) is a noninvasive technique providing cross‐sectional images of the thorax. We have tested an extended evaluation procedure, the functional EIT (f‐EIT), to identify the local shifts of ventilation known to occur during the transition between spontaneous, controlled and assisted ventilation modes.

Pulmonary Functional Imaging: Qualitative Comparison of Fourier Decomposition MR Imaging with SPECT/CT in Porcine Lung

PURPOSE To compare unenhanced lung ventilation-weighted (VW) and perfusion-weighted (QW) imaging based on Fourier decomposition (FD) magnetic resonance (MR) imaging with the clinical reference standard single photon emission computed tomography (SPECT)/computed tomography (CT) in an animal experiment. MATERIALS AND METHODS The study was approved by the local animal care committee. Lung ventilation and perfusion was assessed in seven anesthetized pigs by using a 1.5-T MR imager and SPECT/CT. For time-resolved FD MR imaging, sets of lung images were acquired by using an untriggered two-dimensional balanced steady-state free precession sequence (repetition time, 1.9 msec; echo time, 0.8 msec; acquisition time per image, 118 msec; acquisition rate, 3.33 images per second; flip angle, 75°; section thickness, 12 mm; matrix, 128 × 128). Breathing displacement was corrected with nonrigid image registration. Parenchymal signal intensity was analyzed pixelwise with FD to separate periodic changes of proton density induced by respiration and periodic changes of blood flow. Spectral lines representing respiratory and cardiac frequencies were integrated to calculate VW and QW images. Ventilation and perfusion SPECT was performed after inhalation of dispersed technetium 99m ((99m)Tc) and injection of (99m)Tc-labeled macroaggregated albumin. FD MR imaging and SPECT data were independently analyzed by two physicians in consensus. A regional statistical analysis of homogeneity and pathologic signal changes was performed. RESULTS Images acquired in healthy animals by using FD MR imaging and SPECT showed a homogeneous distribution of VW and QW imaging and pulmonary ventilation and perfusion, respectively. The gravitation-dependent signal distribution of ventilation and perfusion in all animals was similarly observed at FD MR imaging and SPECT. Incidental ventilation and perfusion defects were identically visualized by using both modalities. CONCLUSION This animal experiment demonstrated qualitative agreement in the assessment of regional lung ventilation and perfusion between contrast media-free and radiation-free FD MR imaging and conventional SPECT/CT.