Lung Perfusion Assessment by Bedside Electrical Impedance Tomography in Critically Ill Patients

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.

Keywords: acute respiratory distress syndrome; electrical impedance tomography; lung perfusion; pulmonary embolism; regional ventilation/perfusion match.

Figure 1

Illustrates impedance–time curves and corresponding ventilation/perfusion images during the saline bolus. The tidal impedance variation during normal tidal breathing before apnea was used to calculate the tidal ventilation image. The impedance–time curve caused by saline bolus during the apnea period was used for the perfusion image (adapted from our recent paper).