Bedside electrical impedance tomography to assist the management of pulmonary embolism: A case report

Abstract

Background: Pulmonary embolism (PE) is a common worldwide disease with high mortality. Timely diagnosis and management of PE could significantly improve clinical outcomes. Electrical impedance tomography (EIT) is a novel noninvasive technique to monitor lung perfusion and help detect PE at the bedside. Here we present a case of clinical management of subsegmental PE with the help of the bilateral ventilation and perfusion(V/Q) asymmetry EIT image.

Case presentation: A 72-year-old cancer patient with respiratory failure and acute kidney injury in the intensive care unit was suspected of PE based on his clinical manifestation. The contraindication of computed tomography pulmonary angiography (CTPA) for PE diagnosis prevented escalating anticoagulation therapy. Besides EIT ventilation and perfusion monitoring showed an abnormal asymmetry V/Q match between the bilateral lungs which promoted our decision to start systemic continuous anticoagulation therapy and improved the patient clinically. The following CTPA which clarified the diagnosis of PE suggests that the patient has benefited from our decision.

Conclusion: For critically ill patients with suspected PE, the asymmetry of the EIT V/Q image may provide crucial objective information for clinical management.

Keywords: Asymmetry index; Electrical impedance tomography; Intensive care unit; Lung perfusion; Pulmonary embolism; Ventilation-perfusion.

Fig. 1

Bedside echocardiography and venous ultrasound scan on day one and day two. (A) Flattened intraventricular septum (white arrow) in the diastole, and mildly dilated RV with an estimated ratio of 1:1 between the RV and the LV on day one. (B) Negative bubble test by transthoracic echocardiography on day two. RV: right ventricle; LV: left ventricle. (C) A vein thrombosis was found in the right internal jugular vein.

Fig. 2

EIT ventilation and perfusion (V/Q) change images and computed tomography pulmonary angiography (CTPA) images of the Patient. (A). The global V/Q match accounted for 79.29 % with a dead space asymmetry mainly in the right lung accounting for 14.71 % on day two. (B). The global V/Q match accounted for 80 % with a dead space asymmetry mainly in the right lung accounting for 4.79 % on day 28 after systemic anticoagulation therapy. Left: EIT image of the ventilation distribution. Regions with low-ventilated are shown in blue and high-ventilated in white. Middle: Image of the perfusion distribution. High-perfusion regions are shown in red and low-perfusion regions are shown in blue. Right: Image of the regional V/Q match. Regions with high ventilation and low perfusion are gray, low ventilation and high-perfusion regions are blue, and V/Q matches are yellow. High-ventilated regions: pixels with impedance changes higher than 20 % of the maximum tidal impedance variation in the ventilation image. Low-ventilated regions: pixels with changes lower than 20 %. (C). CTPA on Day 28 showed the embolism in the right lower pulmonary artery branch (red arrow). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3

Post hoc asymmetric analysis of EIT images. (A) asymmetry index (AI) of ventilation and perfusion. The X-axis represents right lung pixels horizontally distributed from the middle (0) to the side (200). The Y-axis represents the bilateral asymmetry index (AI) value of ventilation (Left) and perfusion (Right) calculated by dividing the impedance of the right lung pixel by the sum of the modified impedance of the right lung pixel plus the left symmetrical lung pixel. AI ranges from 0 to 1, and ventilation or perfusion distribution was considered symmetrical if AI = 0.5. (B) Boxplots of ventilation and perfusion AI value. Boxplot center line, median; box limits, upper and lower quartiles; whiskers, 1.5 × interquartile range. (C) Lung images intercepted from computed tomography pulmonary angiography (CTPA).