Tracheobronchial Foreign Body Aspiration Diagnosed with Electrical Impedance Tomography

Background Foreign body aspiration (FBA) in children has a high morbidity, and early diagnosis is the key for preventing acute and chronic respiratory complications. To diagnose FBA, commonly used imaging modalities have limited negative predictive value, and rigid bronchoscopy remains as the gold standard. We present a case where the diagnosis of FBA was made in a novel way with electrical impedance tomography (EIT). Case Presentation. A 19-month-old previously healthy boy was admitted with a clinical diagnosis of respiratory failure secondary to bronchiolitis. Chest X-ray showed bilateral lung hyperinflation. He enrolled in a research study which used EIT to measure the effects of high flow nasal cannula (HFNC) on minute ventilation in children with bronchiolitis. On initiation, the patient had near-normal right lung ventilation (98%) and near-absent left lung ventilation (2%). We discontinued the study and alerted the medical team that we suspected FBA. Further imaging (lateral decubitus films and lung ultrasounds) was also obtained, but was not diagnostic. Rigid bronchoscopy was performed and showed a peanut occluding the left mainstem bronchus (LMB). The peanut was removed followed by complete resolution of the patient's symptoms. Conclusions We believe this is the first reported case of FBA diagnosed via EIT. EIT has been shown to be a useful but underutilized technology for diagnosing respiratory disease. While FBA remains a relatively common cause of morbidity and mortality in children less than age four, early diagnosis remains difficult and requires vigilance. This case illustrates the challenges of relying on chest films and ultrasound to assist with diagnosis and suggests that EIT in combination with a thorough history and physical exam can be used to confirm the presence of FBA.


Introduction
Foreign body aspiration (FBA) is a high morbidity diagnosis for children. FBAs are commonly seen in the emergency room (ER) and in pediatric intensive care unit (PICU). Early diagnosis of FBA is critical to prevent acute and chronic respiratory complications including but not limited to respiratory failure, asphyxia, pneumonia, atelectasis, bronchospasm, air trapping, pneumothorax, bacterial abscesses, and cardiopulmonary arrest [1]. FBA is a difficult diagnosis to make and is commonly missed by experienced physicians, with some centers quoting as high as 44% in delayed diagnosis [2]. Tests used to aid in FBA diagnosis include X-rays and ultrasound, but they are limited by their negative predictive values, so children with suspected FBAs often require general anesthesia and a rigid bronchoscopy. We present a case where the diagnosis of FBA was made in a novel way with electrical impedance tomography (EIT), a noninvasive invasive imaging modality that requires no radiation and can be available quickly at the bedside. EIT uses surface electrodes encased in flexible bands to form real-time tomographic images of a body area. e bands go circumferentially around a body area (in this case, the patient's thorax), and the attached EIT machine uses an electrical current to generate images via impedance differences.

Case Presentation
A 19-month-old previously healthy boy presented in acute respiratory failure with a diagnosis of bronchiolitis and reactive airways. is child had rhinovirus/enterovirus diagnosed via respiratory virus panel (RVP). e RVP, along with his clinical exam, led the medical teams in both the ER and PICU to a clinical diagnosis of bronchiolitis and presumed asthma. e patient clinically deteriorated on bronchodilators, steroids, and high flow nasal cannula (HFNC). On exam, he had asymmetric breath sounds and respiratory distress. Erect anteroposterior and lateral chest X-rays ( Figure 1) were read by the pediatric radiologist as ". . .both lungs appear hyperinflated. . . .decreased lung volume on the frontal view which is felt to be related to patient rotation." e patient was enrolled in a prospective research study which used EIT to measure the effects of HFNC on minute ventilation in children with bronchiolitis.
On initiation of EIT ( Figure 2, Video 1), he had near-normal right lung ventilation (98%) and nearly absent left lung ventilation (2%). We obtained more history and learned the patient had worsened respiratory distress after coughing while eating days prior. We discontinued the study and alerted the medical team that we suspected foreign body aspiration (FBA) and that rhinovirus/enterovirus was a parallel diagnosis. e medical team called the attending pediatric radiologist who reexamined the prior anteroposterior and lateral X-rays. e radiologist confirmed that the images were consistent with hyperinflation due to bronchiolitis, but we agreed to order right and left lateral decubitus chest X-rays and chest ultrasounds to further investigate for FBA. e decubitus films ( Figure 3) were read: "Both lungs are hyperinflated on the decubitus view without significant asymmetry which suggests air trapping secondary to bronchiolitis." Lung ultrasounds were read: "Motion was  2 Case Reports in Pediatrics seen at the bilateral hemidiaphragms, with more motion of the right hemidiaphragm as compared to left." Clinical suspicion for FBA remained high due to the EIT test results and the patient's asymmetric physical exam. Otolaryngology was consulted and subsequently performed a rigid bronchoscopy, where a peanut was found to be occluding the left mainstem bronchus (LMB) (Figure 4). Granulation tissue was seen in the right mainstem bronchus (RMB), which suggests that the peanut was originally in the RMB, but had recently moved to the LMB, potentially after coughing, leading to the patient's acute deterioration. e peanut was extracted followed by complete resolution of the patient's symptoms. e patient was discharged home the subsequent day.

Discussion
We believe this is the first reported case of FBA diagnosed via EIT. While FBA remains a relatively common cause of morbidity and mortality in children less than age four, early diagnosis remains difficult and requires vigilance [1,3]. While diagnostics such as anteroposterior X-rays, decubitus films, and lung ultrasound can sometimes be useful, they have limited negative predictive value, and rigid bronchoscopy remains the gold standard to diagnose FBAs [4]. Rigid bronchoscopy is an invasive procedure requiring general anesthesia and has significant risk [5], while EIT is an underutilized technology that requires no radiation, no sedation, and can be applied easily at the patient bedside. EIT has not before been used for FBA diagnosis, but has been used for determining proper one lung ventilation after endotracheal intubation [6,7]. e EIT device used in this study is FDA approved for use in adults and was approved by the CHLA Institutional Review Board (CHLA-19-00341) for the intended research study. While in this case, the Enlight ® 1800 device was used, and there are now several companies which provide EIT technology at the bedside. EIT is currently underutilized clinically, but the set-up process takes less than 5 minutes and requires soft-flexible bands to be placed circumferentially around the patient's chest and the EIT device. is is the technology which could easily be performed in an outpatient or ED setting if they have an EIT device.
is case itself illustrates the challenges of relying on current more commonly used imaging modalities such as radiographic films and ultrasounds to assist with the (a) (b) Figure 3: (a) Right and (b) left lateral decubitus chest X-rays taken after the EIT device was used in attempt to confirm diagnosis of FBA by more traditional means. e attending pediatric radiologist read these images: "Both lungs are hyperinflated on the decubitus view without significant asymmetry which suggests air trapping secondary to bronchiolitis." Figure 4: Images taken from diagnostic bronchoscopy, displaying a peanut causing near-complete occlusion of the left mainstem bronchus (LMB) and granulation tissue in the right mainstem bronchus (RMB). e RMB granulation tissue suggesting the peanut had recently moved, potentially after coughing, leading to the acute deterioration. e peanut was subsequently removed and the patient improved rapidly.

Data Availability
All data generated or analyzed during this study are included within the article.

Disclosure
An earlier version of this case was presented as an abstract at the American oracic Society, San Diego, CA, the United States, May 14, 2021. is abstract is also published in the online abstracts issue of AJRCCM 2021, https://www. atsjournals.org. e research above was performed as part of employment of the authors at Children's Hospital Los Angeles.

Conflicts of Interest
Dr. Guglielmo graduated fellowship and is now an attending at Loma Linda University Children's Hospital.