$$\rightleftharpoonup{xx}$$
$$\longleftharp{xx}$$,
$$\longrightharp{xx}$$,
Pneumothorax (PTX) is defined as the presence of air within the pleural space. It is a well-recognized medical emergency condition with high mortality rates, especially in neonates with associated risk factors1,2,3. The incidence of PTX is reported to be 1–2% in term infants and 6% in premature infants with respiratory distress2,3. In addition, lung US (LUS) performed on asymptomatic term infants show that the incidence of mild PTX in these patients can be as high as 10%2,3. Risk factors associated with increased incidence of PTX include meconium aspiration syndrome (MAS), respiratory distress syndrome (RDS), and persistent pulmonary hypertension of the newborn (PPHN)4,5,6,7. A 1 min Apgar score ≤ 7 was associated with a 2.67x increased risk of PTX (95% CI 1.14–6.25)8. Increasing peak inspiratory pressure (PIP) during conventional mechanical ventilation has been shown to be a risk factor for PTX, and a PIP increase of 1 cm H2O increases the odds of PTX by 1.46 (95% CI 1.02–2.07)8. The incidence of PTX in infants with a <2,500 g birth weight (BW) increases almost 10x compared to those with a BW ≥ 2500 g8. Notably, PTX is associated with increased mortality, with an odds ratio of 5.27 (95% CI = 1.96–14.17)7. Apiliogullari et al. reported that aggregate mortality was as high as 30% in PTX patients while survivors also had an increased rate of bronchopulmonary dysplasia (4.28x vs. controls)9. Therefore, early and accurate diagnosis followed by adequate treatment is imperative3,4,5,6,7,8,9,10,11,12,13,14. Lately, less expensive US imaging systems have become readily available, and non-ionizing, fast, and repeatable LUS represents an ideal tool for the diagnosis of neonatal PTX.
PTX is traditionally diagnosed by clinical imaging, auscultation, transillumination, and chest X-ray findings. In some cases of non-tension PTX, watchful waiting is warranted. However, large PTX or tension PTX requires prompt evacuation of the air in the pleural space by thoracentesis. Obtaining a chest X-ray image can be time-consuming and prolong the diagnosis of tension PTX. For these reasons, in many neonatal intensive care units (NICUs), LUS is replacing chest X-rays in diagnosing PTX due to its superior sensitivity and specificity15-17. Moreover, LUS has been shown to be more accurate than chest X-rays even for small, non-tension PTX18,19,20,21,22,23,24,25,26,27. LUS signs of PTX were first studied and described in adult critical patients. Patients with suspected PTX were scanned with LUS and computed tomography (CT). LUS signs characteristic of PTX were abolition of lung sliding in the B-mode (corresponding to the stratosphere sign in the M-mode), presence of A-lines, and the lung point. In the same study, abolition of lung sliding alone has a sensitivity of 100% and a specificity of 78% for PTX. Absent lung sliding together with the presence of A-lines had a sensitivity of 95% and a specificity of 94% while lung point alone had sensitivity of 79% and a specificity of 100%18.
Similarly, the usefulness of LUS to diagnose PTX has been described in infants19,20,21,22,23,24. CT could not be used as the benchmark in neonatal patients, thus LUS was compared with chest X-ray and clinical exam findings. Most of the studies included infants with sudden deterioration of their respiratory status, where LUS was performed before or after chest X-ray. The diagnostic accuracy showed a sensitivity of 100%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 100%16,17,18,19. In cases characterized by large PTX, lung point was absent, which consequently decreased the sensitivity of this sign to 75–95%21,22. The average time to perform the diagnostic tests in these studies was 5.3 ± 5.6 min for LUS versus 19 ± 11.7 min for a chest X-ray19. As expected, LUS showed better diagnostic accuracy than chest transilumination19. Keeping in mind that in infants with tension PTX the needle is blindly placed in the second intercostal space at the midclavicular line, it is not surprising to see treatment failure and/or complications6. On the other hand, PTX thoracentesis performed under LUS guidance has shown promising results in infants28,29.
The neonatal Lung Ultrasound Training Base of China, Chinese College of Critical Ultrasound, as well as the World Interactive Network Focused On Critical Ultrasound China branch have organized this international expert panel that reviewed the latest literature related to neonatal PTX diagnosis and treatment aimed at the improvement in the application of LUS-based diagnosis and treatment of PTX.
Patients and timing of the examination
The LUS exam can be used on any neonate in respiratory distress. It is indicated in the following situations: 1) Suspicion of PTX in neonates with sudden deterioration of respiratory status; 2) Before and after thoracentesis.
Lung ultrasonography terminology used in PTX diagnosis
Frequently used ultrasound terms in diagnosis of PTX include: A-line, B-line, confluent B-lines, compact B-lines, alveolar-interstitial syndrome, pleural line, lung sliding, lung pulse, sandy beach sign, and stratosphere sign. The exact definitions of the terms used have been described in detail previously30,31,32,33,34.