key: cord-0742279-dclffzlo
authors: Fakhr, Bijan Safaee; Araujo Morais, Caio C.; De Santis Santiago, Roberta R.; Di Fenza, Raffaele; Gibson, Lauren E.; Restrepo, Paula A.; Chang, Marvin G.; Bittner, Edward A.; Pinciroli, Riccardo; Fintelmann, Florian J.; Kacmarek, Robert M.; Berra, Lorenzo
title: Bedside lung perfusion by electrical impedance tomography in the time of COVID-19
date: 2020-08-07
journal: Br J Anaesth
DOI: 10.1016/j.bja.2020.08.001
sha: 839f7d99019f775ad8da4dd276dfab7f3a0ad245
doc_id: 742279
cord_uid: dclffzlo

nan

Electrical impedance tomography (EIT) is a noninvasive, bedside, radiation-free technology that allows clinicians to monitor and optimize ventilation strategies in realtime 5 6 . More recently, EIT has been used to assess regional lung perfusion in critically ill patients [6] [7] [8] . In a swine study, EIT was equivalent to high-sensitive positron emission tomography in detecting alterations in lung perfusion 9 . An observational study of 68 acute respiratory failure patients showed that the evaluation of dead space with EIT (with a cutoff of 30.4%) results in a sensitivity of 90.9% and a specificity of 98.6% for diagnosis of pulmonary embolism 7 .

An available EIT method for generating lung perfusion maps is a first-pass kinetic approach performed by rapid injection of 10 mL of hypertonic sodium chloride as a contrat agent through a central venous catheter during an end-expiratory hold manoeuver on the mechanical ventilator 6 . It is ideally suited to study the causes of refractory hypoxaemia, monitor disease progression, and the response to intervention in this patient population 10 . Here, we describe use of EIT to diagnose a significant lung perfusion defect and to monitor response to anticoagulation over time until normalization of lung perfusion. Confirmation of pulmonary thrombosis and its resolution was obtained by CTPA.

A 66-yr-old man, who consented to this correspondence, presented to the emergency department with progressively worsening shortness of breath, cough, and fever suggestive for COVID-19 pneumonia. He was severely dyspnoeic, requiring 6 L min -1 of oxygen by nasal prongs (?) to maintain an oxygen saturation of 92-93%. His D-dimer was increased (7,473 ng mL -1 ), consistent with the acute inflammatory process of COVID-19, and suspicion for pulmonary embolism was low. Deterioration of the patient and increasing oxygen requirement resulted in tracheal intubation for respiratory failure (arterial partial pressure of oxygen (PaO 2 ) / fraction of inspired oxygen (FiO 2 ) ratio 247 mm Hg), and he was admitted to the ICU. Real-time reverse transcriptase-polymerase chain reaction testing for SARS-CoV-2 was positive. On hospital day 6, because of progressive deterioration in gas exchange (PaO 2 /FiO 2 =120 mm Hg) despite lungprotective measures including pronation and the initiation of inhaled nitric oxide (iNO), EIT was used to evaluate regional ventilation and pulmonary blood flow distribution.

The patient was evaluated in the prone position while receiving 40 ppm iNO and lungprotective mechanical ventilation with positive end-expiratory pressure (PEEP) of 14 cm H 2 O. EIT showed homogenous ventilation, with dead space estimated at 66% of the tidal volume, and imbalanced perfusion distribution, with a significant discrepancy between the left (64%) and right (36%) lungs (Fig. 1A) . Our findings were consistent with a major perfusion impairment, likely due to pulmonary thrombosis (D-Dimer>10,000 ng mL -1 ). Echocardiography revealed an increased right ventricular systolic pressure (>35 mm Hg) and signs of right ventricular strain despite iNO administration, suggesting the presence of pulmonary hypertension. A bubble test excluded an intracardiac shunt.

As a result, the ICU team started therapeutic anticoagulation with continuous infusion of unfractionated heparin i.v. A second EIT (Fig. 1B) was performed on day 8 and was followed by CTPA (Fig. 1D ) that confirmed segmental and subsegmental right upper lobe pulmonary perfusion defects, matching the location of the deficit indicated by EIT.

Over the subsequent 10 days, the patient improved clinically, with a reduction in Ddimer and an improvement in oxygenation (PaO 2 /FiO 2 =354 mm Hg). A trachesotomy was performed on day 17, and repeat EIT (Fig. 1C) showed homogenous lung perfusion and subsequent CTPA on day 34 (Fig 1E) confirmed resolution of the pulmonary artery filling defects. The D-dimer continued to decrease to 3,222 ng mL -1 .

Ventilatory settings and respiratory mechanics remained virtually unchanged throughout. At hospital day 58, the tracheostomy was closed with oxygen therapy via nasal cannula (1-3 L min -1 ), with discharg to a pulmonary rehabilitation center after 68 days of hospitalization.

Recent radiological, physiological, and pathological studies suggest a possible central role for pulmonary vascular alterations in the pathophysiology of COVID-related hypoxaemia 2 3 . We found that EIT detected imbalance in lung perfusion despite even distribution of ventilation in a patient who was later confirmed to have pulmonary thrombosis. EIT was also effective in showing resolution of the perfusion defects following treatment. Follow-up CTPA provided evidence for resolution of clots confirming what was observed with the EIT.

EIT is a radiation-free, noninvasive bedside technique that allows individualized ventilation setting 6 ; identification of perfusion impairment that might require CTPA 7 ; and J o u r n a l P r e -p r o o f multiple assessments of pulmonary perfusion over time to determine response to therapies.

LB is supported by US NIH/NHLBI grant #K23HL128882, receives devices and equipment from Praxair Inc. and Masimo Corp, and has a grant from iNO Therapeutics LLC. RMK is a consultant for Medtronic, Orange Med, and has received research grants from Medtronic and Venner Medical (Dänischenhagen, Germany). All other authors have no conflicts to declare.

A-C. Electrical Impedance Tomography (EIT) perfusion images obtained at days 6, 8, and 18. Images were generated by Enlight 1800 (Timpel SA, São Paulo, Brazil) using the first-pass kinetics method. The lung is divided into 4 quadrants (Regions of Interest). Color scale was adjusted by linear normalization. D. Axial computed tomography pulmonary angiography image shows segmental and subsegmental pulmonary emboli in the right upper lobe (red arrow). E. Axial computed tomography pulmonary angiography image shows resolution of the pulmonary artery filling defect (red arrow) in comparison to the previous image. Day, day from admission to emergency department; C RS, respiratory system compliance; ∆P, driving pressure.

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