Abstract
It is crucial to precisely monitor ventilation and correctly diagnose ventilation-related pathological states for averting lung collapse and lung failure in Intensive Care Unit (ICU) patients. Although Electrical Impedance Tomography (EIT) may deliver this information continuously and non-invasively at bedside, to date there are no studies that systematically compare EIT and Dual Energy CT (DECT) during inspiration and expiration (ΔDECT) regarding varying physiological and ICU-typical pathological conditions such as atelectasis. This study aims to prove the accuracy of EIT through quantitative identification and monitoring of pathological ventilation conditions on a four-quadrant basis using ΔDECT. In a cohort of 13 pigs, this study investigated systematic changes in tidal volume (TV) and positive end-expiratory pressure (PEEP) under physiological ventilation conditions. Pathological ventilation conditions were established experimentally by single-lung ventilation and pulmonary saline lavage. Spirometric data were compared to voxel-based entire lung ΔDECT, and EIT intensities were compared to ΔDECT of a 12-cm slab of the lung around the EIT belt, the so called ΔDECTBelt. To validate ΔDECT data with spirometry, a Pearson’s correlation coefficient of 0.92 was found for 234 ventilation conditions. Comparing EIT intensity with ΔDECT(Belt), the correlation r = 0.84 was found. Normalized cross-correlation function (NCCF) between scaled global impedance (EIT) waveforms and global volume ventilator curves was r = 0.99 ± 0.003. The EIT technique correctly identified the ventilated lung in all cases of single-lung ventilation. In the four-quadrant based evaluation, which assesses the difference between end-expiratory lung volume (ΔEELV) and the corresponding parameter in EIT, i.e. the end-expiratory lung impedance (ΔEELI), the Pearson’s correlation coefficient of 0.94 was found. The respective Pearson’s correlation coefficients implies good to excellent concurrence between global and regional EIT ventilation data validated by ventilator spirometry and DECT imaging. By providing real-time images of the lung, EIT is a promising, EIT is a promising, clinically robust tool for bedside assessment of regional ventilation distribution and changes of end-expiratory lung volume.
Highlights
Electrical Impedance Tomography (EIT) is a non-invasive bedside monitoring technique, that uses an electrode belt stretched around the thorax to measure the intrathoracic resistivity and its changes during breathing
The latter aspect is important for patients with mechanical ventilation on an intensive care unit (ICU): gravity-dependent lung collapse or atelectasis induces pathologic ventilation distribution of the lung which is generally not reflected in changes in global ventilation parameters or airway pressure spirometry data
In 234 ΔDECT of the whole lung, the mean tidal volume was calculated as 570.42 ± 134.93 ml
Summary
Electrical Impedance Tomography (EIT) is a non-invasive bedside monitoring technique, that uses an electrode belt stretched around the thorax to measure the intrathoracic resistivity and its changes during breathing. Global spirometry data, which reflect the condition of the lung as a whole, cannot detect focal pathologies such as atelectasis or pleural effusion with sufficient certainty Due to these drawbacks of both techniques, CT and spirometry, the continuous assessment of regional ventilation distribution — namely, of how different lung regions respond to therapeutic interventions over time — is mostly unclear in clinical routine. This calculation of ΔCT provided dynamic information about regional ventilation distribution as well as information on global and regional air volume changes, using a slice thickness of 2–8 mm To address this lack of validation data our study investigated typical pulmonary pathologies in a porcine model resembling clinical scenarios observed in ICU patients. Global and regional EIT data were compared to ventilator spirometry and global and regional ΔDECT data
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