Our study provides the first results relating EIT ventilation profiles to TCT or chest radiograph findings in COVID-19 pediatric patients.
Recently published data on EIT use in the pediatric population states that this technology “seems to be predestined for the clinical use in neonates, infants and children”, since it is a radiation free imaging tool that does not need patient collaboration. Moreover, EIT can be used for prolonged periods, at the bedside, in the PICU and NICU environments. This study points the EIT ability to explore air distribution, to determine the center of ventilation, to analyze the inhomogeneity index of air distribution and estimate the tidal volume and FRC, aspects that are considered highly significant to the researchers using this technology, some of them presented at our data on COVID-19 children [12].
Previous validation data confirm that EIT is a highly reproducible method in which impedance changes accurately reflect regional ventilation variations [9, 11]. The EIT validation study compared impedance evaluation results, initially considered as a lung functional image, to TCT images, considered a hallmark of anatomic air distribution within the lungs, and with a very consistent result [9].
The ventilation distribution ratio present in the asymptomatic patients in our study was in accordance to previously published data in spontaneously breathing healthy children, where pulmonary ventilation distribution is predominantly directed to the posterior (65–70%) and right (52–55%) lung regions [13, 14]. Nevertheless, different data observed that the ventilation pattern in healthy children is quite variable when compared to a more well-established pattern reported in adults [13].
In our presented cases, the abnormal ventilatory profiles found, particularly in the right-left distribution, agreed with the morphological changes found in the TCT or the chest radiograph images due to COVID-19 infection. Li W et al. described the findings of five children positive for COVID-19, four of whom were asymptomatic, and one presented only mild respiratory symptoms. Two patients had no abnormalities detected through TCT, while the other three presented a very modest form of ground-glass opacification [7]. Of the six patients in our study, two underwent chest TCT and had a ground-glass pattern, and one of them had pleural effusion. The EIT pattern differed between them, since patient 2 presented a more uneven distribution of the disease which affected more the left lower lung (Fig. 1).
Although the performance of the TCT was also recommended for the pediatric population as one of the clinical criteria for the diagnosis of COVID-19 early in the pandemic, some points were reconsidered for the non-routine performance of the exam. The images in the pediatric population are more nonspecific than in adults to be used as a diagnostic criterion, and in many cases with confirmed RT-PCR for the virus, TCT images are normal [15, 16]. In addition, radiation exposure should be considered for the indication and need for TCT [17]. Additionally, recent concerns were raised in the pediatric population exposed to ionizing radiation, since there is evidence of increased cancer development in this population [18, 19]. According to the Guideline for Medical Imaging in Auxiliary Diagnosis of COVID-19, the accompanying images can be made by radiograph exams [15].
EIT is radiation-free, portable, and easily performed at the bedside, and can be useful in the management and evaluation of pediatric patients with respiratory diseases, including COVID-19. In addition, the EIT data on ventilation distribution and EELZ, a surrogate of functional residual capacity, provides new information on patient monitoring and can assist titration of the respiratory support. In one of our presented cases, patient 4 needed noninvasive support due to respiratory failure and was evaluated in three positions. The EIT information demonstrated that the left lung ventilation was strongly compromised under the action of gravity, and left lateral decubitus was avoided, possibly helping in the patient outcome.
Recently EIT published data depicted self-inflicted lung injury mechanism, named “Pendelluft”, in a P-ARDS infant and in a preterm infant treated with minimally invasive surfactant therapy [20, 21]. In those low compliance respiratory illness, EIT can monitor changes in air distribution and detect the lung recruitment at the bedside, as was already reported in adults both in the ICU and during anesthesia [22, 23]. Although large series are not yet available in the pediatric population, we believe that EIT help tailoring ventilatory support in many situations based on the different reports already published [24,25,26].
One of the limitations of our study was the small number of children included due to the reduced number of children hospitalized secondary to COVID-19, since a milder disease in children is the usual presentation [27, 28]. In our service, there were only seven hospitalizations in the PICU during the study period, and this was shown to be strongly determined by the social isolation measures implemented in Sao Paulo to contain new COVID-19 cases during the pandemic, including closing schools and daycare centers, which drastically interfered with the seasonality of respiratory diseases in the pediatric population [29].