In this study, we found that a rapid combined clinical and ultrasound score was accurate for discriminating during the first clinical evaluation the risk for PICU admission and CPAP ventilation in children with bronchiolitis. To our knowledge, this is the first study including evaluating a relatively large number of children requiring PICU and using a score that combines both clinical and ultrasound information.
The use of lung ultrasound is rapidly growing worldwide and scientists are expanding its clinical use and physical knowledge in both adult and pediatric practice, including neonatology [1].Specifically, to the initial use of LUS in pleural effusions and pneumonia, several other applications including interstitial lung disease, traumas, pneumothorax, acute respiratory distress syndrome, neonatal RDS, TB and bronchiolitis have been added and further investigated [1].
In paediatrics, a large number of studies have focused on bronchiolitis [2–15]. It is now well established that LUS can detect different patterns of lung involvement in children with bronchiolitis, including vertical artifacts and different-size subpleural consolidations, which, according to a recent study with a standardized follow-up, seem to be mostly peripheral areas of disventilation/atelectasis given their rapid resolution [15]. Moreover, previous studies using different ultrasound approaches showed that children with bronchiolitis have frequent posterior paravertebral small consolidations or that patients requiring oxygen or ventilation usually have higher LUS scores, however with large overlaps of LUS scores between the different groups and mostly including small or no patients needing PICU admission [2–15]. This overlaps on one hand may imply a low accuracy of LUS in predicting bronchiolitis severity, on the other may highlight that our use of this tool can still be improved.
On this regard, experience can be gained by adult and neonatal practice, as well as knowledge of the physical bases of lung ultrasound. Experts from adult and neonatal practice are suggesting that the semi-quantification of LUS scores may be used as a tool to quantify the aeration of the peripheral lung, and this is particularly evident from several studies from De Luca’s team on preclinical and clinical data on neonatal respiratory conditions[23–27]. The rationale for such an approach is the relatively obvious hypothesis that the less the peripheral lung is expanded, the less lung areas are available for gas exchanges and, therefore, the clinical manifestation of that specific disease is expected to be more severe. These hypothesis has, importantly, fundaments on the growing knowledge of the bases of LUS and specifically from several studies of the Italian Academy of Thoracic Ultrasound, coordinated by Soldati et al, which demonstrated that vertical artifacts, white lung and consolidations are expression of a spectrum of increasing loss of the peripheral alveolar structure up to the total hepatisation of the lung, which does not contribute anymore to gas exchange[28–32]. While this is all true, clinical observations from several studies, from COVID-19 to bronchiolitis, show that although most severe patients have usually higher LUS scores, use of LUS scores may be limited in predicting disease severity, suggesting that other parameters beside the status of peripheral lung (which is the lung area that can be explored with LUS), contribute to pathophysiology.
For example, bronchiolitis is frequently characterized by wheezing[33].Interestingly, in fact, in our cohort the patients admitted to PICU had significantly higher rates of wheezing, while those not admitted mostly have upper respiratory involvement with rhinitis. However, wheezing has not a direct consistent pattern/expression on LUS, and therefore excluding such an important parameter from a severity-predicting score would make no sense. Indirectly, the bronchial obstruction could cause a peripheral disventilatory picture downstream of the obstruction which can leads to an indirect visibility subpleural consolidation, as previously described also by our team in a case series [34]. However, it is currently unknown if every functional wheezing leads to peripheral dysventilation and, therefore, we cannot speculate that every wheezing has a concomitant ultrasound-visible atelectasis, and more importantly there is no grading in the current literature linking severity of wheezing with dimension of peripheral atelectasis. Therefore, although there is space for future research to better understand how wheezing can be seen and quantified through indirect LUS features, at the moment we believe that the clinical finding of wheezing (the sound) is easier to be documented compared with the LUS pattern, and therefore we suggest to include wheezing in the clinical prediction rules of bronchiolitis-severity, in adjunction of the LUS features.
Wheezing is expression of bronchial obstruction, and since bronchi do not touch the pleura they cannot be explored by ultrasounds. Also, reduced oral intake is one of the most important complications in more severe disease and, obviously, no LUS patterns can detect this. This observation induced us to unify clinical and LUS parameters. Importantly, the concept that LUS is an adjunctive clinical tool that should add to the clinical examination has already been established, and previous studies have already demonstrated that the use of both clinical and LUS parameters significantly improve the accuracy of patient assessment compared with clinical or LUS used independently [18]. Interestingly, in our score including the most important clinical and LUS on the univariate models, we found that including both wheezing and LUS parameters gave a very accurate model for predicting PICU admission and CPAP need. To our knowledge, such a combination of easy and relevant clinical and LUS parameters has never been studied before and, importantly, its high accuracy is very promising.
In our combined LUS-clinical score, the most relevant areas of the lung for prediction of need of high support were the posterior ones. Several studies have documented that common lung diseases, including bronchiolitis, neonatal RDS, and recently COVID-19, are commonly characterized by involvement of the posterior lung areas. This finding may be also due to the frequent supine positions of young infants and the consequent gravitational deposits of airways secretions or a less ventilation of these areas [35]. Regional atelectasis is potentially easier to be found in infants and children, as the relative and absolute airway diameter is smaller compared to adults, thus, smaller volumes of secretions are needed to occlude them [36]. The involvement of the right upper zone and the left basal one (both posteriorly) has been already described [37]. Potential explanations for this preferential atelectasis can be looked for in the anatomy - the right upper lobe bronchus arises at a 90-degree angle from the right mainstem bronchus [38]- or in its the position in space - the right upper lobe is the most dependent bronchus in the supine position, making it a steeper way to clear secretions [39]; the left posterior basal area, also, could be involved because compressed by the heart [36].
Also, in our population, lateral areas scores were significantly different in those admitted to PICU and in those ventilated in CPAP compared to those who were not. Infants with bronchiolitis, in particular the most severe ones, are usually still breastfed/formula fed and the usual positions for milk feeding requires the infant being in a supine but partially lateral position. This may somehow predispose to microaspirations that gravitationally deposit on lateral area, which in turn appear less ventilated on LUS. Also, the tridimensional dinamics of thorax motion during breathing and growth is still unclear, although very recent advances suggest that different part of the thorax may contribute differently during respiration and that this may change with development [40–42]. This may lead to the speculation that lateral sections of the ribs are less expanded during pathological breathing in more severe bronchiolitis, since children mostly use the diaphragm and other accessory muscles like sternocleidomastoideum muscles, and therefore those areas are more easily atelectatic. These hypothesis requires, obviously, further confirmations but, in our opinion, were strong and interesting enough to require validation and also new pathophysiology studies.
A strength of our model is its simplicity. As clinicians involved in routine clinical practice, we focused our efforts under a pediatric emergency medicine/intensive care perspective. In these settings, it is pivotal to have tools that are quickly and easily feasible at patient bed-side. Although several associations, including the ADET and also our previous studies, have highlighted the importance of a comprehensive assessment of all lung areas while performing LUS, in very urgent settings scanning all lung areas is not feasible. Therefore, a quick tool like ours can serve as a useful first assessment that might serve in better triaging children with bronchiolitis assessed in the paediatric emergency department, and leaving a more comprehensive LUS assessment during follow-up visits in children hospitalized. For example, predicting which infants with bronchiolitis will develop severe disease later during disease course is still a challenge, as re-visits in the PED of previously discharged children coming back with worsening bronchiolitis are still a problem with organizational and legal consequences [43]. In this setting, our approach, if confirmed by other studies, can have a positive impact on the management of bronchiolitis.
Our study has limitations, mainly the relatively small number of children included, particularly for the PICU group, and the absence of patients requiring invasive ventilation. However, this is still the largest cohort including PICU patients.
In conclusion, we developed a combined clinical-ultrasound score able to accurately predict need of PICU admission and CPAP ventilation in children with bronchiolitis. Hopefully, given the very promising findings of our study, we hope that this model will be tested in further multicentric studies including larger cohorts of patients, since such a rapid tool may significantly improve the initial assessment of children with bronchiolitis.