Lung ultrasound outperforms conventional radiology in the emergency diagnosis of pneumothorax and pleural effusions. Neonatologists and pediatricians are now adapting lung ultrasound to their specific clinical issues. The normal image is relatively unchanged throughout the age span, whereas progressively fading B-lines (comet-tail artifacts) describe the fluid-to-air transition of the neonatal lung. Also, an homogeneous white (hyperechogenic) lung with pleural image abnormalities and absence of spared areas is accurate in diagnosing respiratory distress syndrome. The evidence of bilateral confluent B-lines in the dependent areas of the lung (‘‘white lung’’) and normal or near-normal appearance of the lung in the superior fields is highly sensitive and specific for transient tachypnea of the newborn. Infantile pneumonia has recently been proved to be accurately diagnosed by ultrasound after a short training period. In summary, chest ultrasonography is not yet ready to replace conventional chest radiology. However, when appropriately applied, a lung ultrasound scan can save time and radiation exposure to achieve a critical diagnosis.
After completing this article, readers should be able to:
Understand the propagation of ultrasound through the chest and the meaning of the main artifactual images.
Correlate profiles of ultrasound artifacts with specific lung diseases.
Appreciate the current clinical literature validating point-of-care lung ultrasound in pediatrics and neonatology.
Neonatal respiratory disease is currently diagnosed on the basis of clinical signs and chest radiograph. Wilson–Costello (1) has estimated that an average of 31 radiographs are taken during the hospital admission of an extremely low birthweight infant. The relevance of this radiation exposure is still debated. Moreover, the interpretation of a chest radiograph has a significant interobserver variability. Ultrasound imaging of the lung has been traditionally neglected because the high acoustic impedance of its air content prevents a clear image of the organ. Ultrasound penetrating an aereated lung will produce artifacts (ie, structures not naturally present in living tissue, which appear as authentic images). These imagery anomalies come from the machine acquisition of the ultrasound beam path through means with markedly different acoustic impedance (eg, air, tissue, fluid) in close proximity. The pleura is the only lung part clearly visible with ultrasounds appearing as an homogeneous, hyperechogenic line moving synchronously with respiration. The pioneering work of Lichtenstein and other adult emergency physicians has revealed that the interpretation at the patient bedside of these findings together with some reproducible artifacts can be very useful in critical situations where lung ultrasound outperforms conventional radiology. The fundamentals of this technique, which hold true irrespective of the patient’s age, have been recently reported in international evidence-based recommendations. (2)
Many pediatricians and neonatologists have learned the lesson and are now applying point-of-care lung ultrasound to their practice. This article is a concise but comprehensive summary of recent work in this area.
From Artifacts to Clinical Correlates
A microconvex or convex probe is generally used to explore the adult chest. A linear, high frequency device is preferred in neonates where it grants a wide view of the anterior, lateral, and posterior fields both in the longitudinal and transverse projections. In the healthy infant, a periodically moving line will be evident in B-mode below the superficial planes and between the rib images. This horizontal motion corresponds to the sliding of the pleural leaflets (the sliding sign). A vertical motion of pleural line, synchronous with cardiac activity (the lung pulse sign) is observed in the nonventilated lung or in lung atelectasis.
Inferiorly, the pleural image is reflected a number of times in straight and short repetitions also known as A-lines (Fig 1).
A different artifact is named B-line, a vertical hyperechoic image that recalls the tail of a comet (Fig 2). B-lines are thought to originate from reverberations among bubbles with a critical radius. They are present when the partition between the aerated and the tissue-fluid part of the lungs is altered. B-lines can be seen as individual or multiple artifacts with a trend to coalesce into a white lung image of sicker patients (Fig 3). In the adult, B-lines have been linked to the interstitial syndrome and may also be useful in evaluating the patient who has heart failure. (3)(4)(5)(6) In the neonate, sporadic B-lines are often present after birth, especially after cesarean delivery (probably because of retained lung fluid), but a white lung image is never regarded as normal.
Lung consolidation on ultrasonography is visualized as a subpleural echopoor or tissuelike region with blurred margins or wedge-shaped borders. (7) Therefore, significant atelectasis or pneumonia is the only circumstance where a real image of the lung parenchyma is generated by ultrasounds. Sonographic air bronchograms are hyperechoic linear elements representing air in bronchioles that appear within the hypoechoic consolidated lung (Fig 4).
In adults, the evidence of dynamic air bronchograms rules out obstructive atelectasis with a specificity of 100%. (8) Lung ultrasound is very accurate in detecting pneumothorax although its volume cannot be estimated.
The diagnosis comes from the simultaneous absence of B-lines, lung sliding, lung pulse, and the evidence of “lung point(s).” The latter is the echographic demonstration of the pneumothorax borders; it appears as an area where a still pleura (with underlying air collection) meets the sliding pleural leaflets of normally functioning lung.
Pleural effusions appear as an anechoic space between the pleural leaflets. Lung ultrasound is very accurate for the diagnosis of complicated pleural effusion (Fig 5). Conventional radiology detects as opacities images that will be differentiated as consolidations or effusion only by ultrasound scan. It is not surprising, then, that lung ultrasound outperforms the radiograph in ruling in and out both pneumothorax and effusions in the adult. (9)(10)(11)(12) In the neonate and child, these comparative studies have not yet been published, but experienced pediatric clinicians do not refrain from resorting to the aid of ultrasound for these diagnoses.
“Field Validation” of Lung Ultrasound in Neonatology and Pediatrics
Neonatologists and pediatricians are gathering evidence-based data on ultrasound diagnosis of those respiratory diseases that more frequently affect the developing age.
Respiratory distress syndrome was diagnosed by Copetti et al (13) with the simultaneous presence of three ultrasound findings: abnormalities of the pleural line, white lung image, and absence of spared areas in all lung fields (Fig 6). This profile had sensitivity and specificity of 100% in their series of 55 premature infants. (13) The high diagnostic accuracy may allow a better individualized surfactant administration saving costs and minimizing the duration of ineffective breathing.
Unfortunately, because the intratracheal administration of surfactant does not clear the picture, (13) chest ultrasound has limited value in the immediate follow-up of respiratory distress syndrome.
The same group also found that the presence of a double lung point (normal or near normal upper lung fields with coalescent B-lines in dependent areas) was highly sensitive and specific for transient tachypnea of the newborn (Fig7). (14)
A population of 154 unselected term and late preterm newly born infants recently underwent sequential chest ultrasound scans in a well-baby nursery. (15) The normal clearance of lung fluid was documented with progressive disappearance of B-lines to A-lines. Also, a white lung image at 2 hours after birth was always associated with clinically significant respiratory distress and need of ventilatory support. Lung ultrasound is therefore a rapid and efficient screening technique to be used in level 1 birth centers to grant respiratory assistance in a timely fashion.
Finally, a large study was conducted on pediatric patients (median age, 3 years; interquartile range, 1–8) at two American emergency departments testing the ability of point-of-care lung ultrasound to diagnose pneumonia by using the chest radiograph as a reference standard. (16) Clinicians who had received training in chest ultrasound as short as 1 hour were able to accurately diagnose pneumonia with an overall sensitivity of 86% and a specificity of 89% by visualizing lung consolidation with sonographic air bronchograms. In the subgroup analysis of 187 patients having lung consolidation exceeding 1 cm, ultrasonography had a sensitivity of 86%, whereas specificity rose to 97%.
The ultrasound exploration of the lung has rapidly gained an important role in emergency diagnostics. It complements rather than substituting for conventional radiology, but, where appropriately applied, chest ultrasound saves time and radiation exposure. The ultrasound scan of the lungs does not offer a full vision of the organ but generates a number of artifacts that must be interpreted, often after a steep learning curve, to accurately diagnose critical disease in the adult. Neonatologists and pediatricians are now applying, with success, point-of-care lung ultrasound to provide better care for their fragile patients.
American Board of Pediatrics Neonatal-Perinatal Content Specifications
Recognize the clinical, imaging, and laboratory features of respiratory distress syndrome.
Know the pathophysiology of air leaks.
Drs Raimondi, Cattarossi, and Copetti have disclosed no financial relationships relevant to this article. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.
- Copyright © 2014 by the American Academy of Pediatrics
- Wilson-Costello D,
- Rao PS,
- Morrison S,
- Hack M
- Volpicelli G,
- Elbarbary M,
- Blaivas M,
- et al
- Agricola E,
- Arbelot C,
- Blaivas M,
- et al