Abstract
As a portable, radiation-free imaging modality, electrical impedance tomography (EIT) technology has shown promise in the bedside visual assessment of lung perfusion distribution in critically ill patients. The two main methods of EIT for assessing lung perfusion are the pulsatility and conductivity contrast (saline) bolus method. Increasing attention is being paid to the saline bolus EIT method in the evaluation of regional pulmonary perfusion in clinical practice. This study seeks to provide an overview of experimental and clinical studies with the aim of clarifying the progress made in the use of the saline bolus EIT method. Animal studies revealed that the saline bolus EIT method presented good consistency with single-photon emission CT (SPECT) in the evaluation of lung regional perfusion changes in various pathological conditions. Moreover, the saline bolus EIT method has been applied to assess the lung perfusion in a pulmonary embolism and the effect of positive end-expiratory pressure (PEEP) on regional ventilation/perfusion ratio (V/Q) and acute respiratory distress syndrome (ARDS) in several clinical studies. The implementation of saline boluses, data analyses, precision, and cutoff values varied among different studies, and a consensus must be reached regarding the clinical application of the saline bolus EIT method. Further study is required to validate the impact of the described saline bolus EIT method on decision-making, therapeutic management, and outcomes in critically ill patients.
Highlights
The evaluation of regional pulmonary perfusion is of great interest for cardiopulmonary management in the intensive care unit (ICU)
We summarized the clinical studies using pulsatility-based electrical impedance tomography (EIT) assessments for pulmonary perfusion in healthy volunteers and patients with pulmonary hypertension (PH) (Table 1)
Borges JB et al found that pulsatile impedance increased within the collapsed lung region, which had reduced lung blood flow based on both the single-photon emission CT (SPECT) and saline bolus EIT methods (Borges et al, 2012)
Summary
The evaluation of regional pulmonary perfusion is of great interest for cardiopulmonary management in the intensive care unit (ICU). Recent years have witnessed substantial progress in this area, and several techniques for pulmonary perfusion assessment, including MRI, CT, PET, and single-photon emission CT (SPECT), have become available (Hopkins et al, 2012; McCollough et al, 2015; Bondesson et al, 2019; Kohli et al, 2019) These methods are rarely used in critically ill patients because of the non-bedside implementation, high risk of transfer, inconvenience, etc. Borges JB et al found that pulsatile impedance increased within the collapsed lung region, which had reduced lung blood flow based on both the SPECT and saline bolus EIT methods (Borges et al, 2012). Following the administration of a saline bolus, by calculating the SD of each pixel and plotting them at the relevant image position, a new type of EIT image presenting the exact position, into which the indicator is carried by the bloodstream and visualizing the temporal variation in perfusion distribution can be generated (Frerichs et al, 2002)
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