Surfactant deficiency syndrome in premature infants is a good example of the use of ultrasound as a diagnostic tool. In 2008, the Italian authors of one of the first publications demonstrated high sensitivity and specificity the LUS in identifying RDS. The atelectatic nature of the lung tissue, with varying degrees of interstitial thickening, is reflected on ultrasound in an increasing number of B-lines up to the image of an alveolar-interstitial pattern with subpleural consolidation (alveolar oedema, fluid alevologram) and deeper atelectasis in the most severe cases. Lung ultrasound seminology was published by Raimondi et al. (7). Identification of RDS with a sensitivity and specificity of 100% can occur if three abnormalities are present at the same time: alveolar-interstitial pattern (image of the “white lung”), pleural line abnormalities (small subpleural consolidations, thickening, irregularity and rough appearance) and affecting all areas of the lungs (Figures 1, 2. Supplementary Data—Videos S1, S2) (8).

The place of ultrasonography in diagnosing RDS and determining treatment has been established in the “European Consensus Guidelines on the Management of Respiratory Distress Syndrome: 2022 Update” in three areas: diagnosis of RDS, assessment of its severity, monitoring of complications and effectiveness of treatment. Currently, the indications for surfactant administration are based on clinical signs indicating respiratory distress in the newborn. Early use of nCPAP avoids the risks associated with endotracheal administration of surfactant. Deterioration of respiratory capacity will be an indication for surfactant administration (9).

In 2015, the RDS severity score scale, described by Brat et al., was used for the first time in the ultrasound evaluation of RDS (10). Over the years, there have been published studies using various modifications of this scale (both in terms of the number of lung fields analysed and the degrees of severity of the lesions). The value of various modifications of this scale is discussed in (11). The important limitation is the subjectivity in image interpretation, which may affect interobserver agreement, particularly in borderline or complex cases.

The ultrasound-based RDS severity scale (LUSs) is a tool that enables prediction of the need for surfactant therapy, repeat administration, escalation of respiratory support to mechanical ventilation, and even the risk of developing bronchopulmonary dysplasia (BPD) (10, 12–14).

The effects of administered surfactant can be monitored ultrasonographically (13). During endotracheal administration of the drug, displacement of the contents in the right and left bronchi can be observed, making sure of the symmetry of deposition in the lungs. Sometime after administration, it is advisable to assess the improvement of lung airflow—the appearance of A-line artifacts, reducing the number of B-lines. Due to the tendency to administer more drug to the right bronchus—it is possible to observe asymmetry of lung aeration—weaker aeration of the left lung. This heterogeneous picture indicates an increased risk of complications in the form of pneumothorax.

Asymmetric surfactant administration can result from deep position of the endotracheal tube. This can be prevented by assessing the position of the tube tip with ultrasound. A recent meta-analysis shows that LUS is a quick and effective technique for identifying the correct endotracheal tube position in neonates (15).

The study of lung recruitment maneuver in intubated patients with RDS under ultrasound guidance (ultrasound scale was used) was interesting. Reduction in the risk of atelectasis was associated with a better prognosis—faster reduction in oxygen requirements, shorter NICU stay, reduced inflammation, and shorter mechanical ventilation time (16).

Transient tachypnea of the newborn (TTN) is a frequent cause of perinatal dyspnea. TTN is characterized as a self-limited respiratory disorder resulting from delayed clearance of fetal lung fluid (17). The incidence of TTN ranges from 4% to 5.7% in full-term neonates and reaches approximately 10% in preterm infants (18). Although TTN is typically a temporary condition, the associated dyspnea can be clinically significant. The primary clinical challenge involves distinguishing TTN from other etiologies of neonatal respiratory distress, such as respiratory distress syndrome (RDS), pneumonia, and meconium aspiration syndrome. Copetti et al. introduced LUS for the diagnosis of TTN and defined a “double lung point” (DLP), which refers to the distinct boundary between lower lung regions displaying a hyperechoic, thin pleural line with compact B-lines and upper lung areas that are normal or nearly normal (19). Besides DLP, ultrasound findings of TTN include interstitial syndrome or “white lungs,” pleural line abnormalities, loss of A-lines, and pleural effusions (20). According to meta-analyses published in 2021, LUS demonstrated a pooled sensitivity of 0.67 (95% CI = 0.63–0.71) and specificity of 0.97 (95% CI = 0.95–0.98) for diagnosing TTN (21). A recent systematic review and meta-analysis conducted by Ma et al. reported that lung ultrasound (LUS) demonstrated a pooled sensitivity of 0.98 (95% CI: 0.92–1.00) and specificity of 0.99 (95% CI: 0.91–1.00), with an area under the curve of 1.00 (95% CI: 0.98–1.00) (22). Wang Y noted that DLP's effectiveness in diagnosing TTN differs widely across studies (sensitivity 100–45.6%, specificity 100–94.8%). Using DLP together with B-line as a diagnostic standard may greatly enhance LUS accuracy (23).

Considering recent reports, LUS demonstrates up to 100% sensitivity and specificity in the diagnosis of PTX in neonates (24–27). It has been included in the recommendations of the PoCUS Working Group of the European Society of Paediatric and Neonatal Intensive Care (ESPNIC) regarding the diagnosis and treatment of pneumothorax (28). Lung PoCUS, including the exclusion of PTX, is also an integral part of protocols such as the Crushing Neonate Protocol (CNP) and the Sonographic Assessment of liFe-threatening Emergencies—Revised (SAFE-R) (29, 30). Among the key advantages of ultrasound in AIS—particularly PTX—are its ready availability and rapid execution, significantly shortening the time needed for diagnosis (31, 32).

For ultrasound in suspected PTX, a high-frequency linear probe is used, and the neonate is positioned supine. The first step in the evaluation is assessing the position of the mediastinum (especially the thymus, which is easily recognizable on ultrasound) and ruling out any significant shift of mediastinal structures relative to the centrally located sternum, which is characterized by a hyperechoic ossification nucleus and a posterior acoustic shadow (Supplementary Data—Video S3). A significant shift of mediastinal structures toward the midline, caused by the free air chamber, allows for the diagnosis of tension pneumothorax (Figure 3). The anterior transverse plane showing loss of mediastinal structures and visible A-lines beneath the sternum demonstrates high diagnostic accuracy: sensitivity 99.0%, specificity 100%, PPV 100%, and NPV 98.8% (33). When the transducer is placed over the lung fields in the case of pneumothorax, the following findings are expected: absence of the normal pleural sliding sign, an overrepresentation of A-line artifacts (reverberations at the air pocket interface), absence of B-line artifacts (which arise due to small amounts of fluid in interlobular septa), and absence of lung pulse—the transmission of cardiac pulsations to the pleural line (25, 26).

In uncertain cases, diagnostic accuracy can be enhanced using M-mode ultrasound: in PTX, the overrepresented A-lines below the pleural line will create the so-called “barcode sign” or “stratosphere sign” (Figure 4), replacing the normal granular pattern known as the “seashore sign”. A key advantage of lung ultrasound is the ability to precisely locate the border of the air pocket by identifying the so-called lung point—the site where pleural sliding disappears (Figure 5, Supplementary Data—Video S4) (26, 27). If decompression of the pneumothorax is necessary, the exact margins of the trapped air in the pleural cavity can be accurately determined after properly positioning the infant, thereby guiding the site for needle insertion or chest tube placement (34).

Ultrasound can also be effectively used to verify the outcome of pneumothorax decompression. Indicators confirming successful drainage or aspiration include the return of mediastinal structures to the midline, disappearance of the lung point, reappearance of pleural sliding, and the presence of B-line artifacts. Additionally, the presence of the chest tube in the pleural cavity can be confirmed by visualizing its passage through the parietal pleura between the ribs.

The presence of free air in the mediastinum is most often an incidental finding accompanying signs of respiratory distress during PTX or pulmonary interstitial emphysema (PIE). In ultrasound, pneumomediastinum (PM) should be suspected when free air in the mediastinum (overrepresented A-line artifacts due to reverberations at the air interface) prevents evaluation of mediastinal structures, particularly the heart, during echocardiographic examination (Supplementary Data—Video S5). In most cases, this is a transient phenomenon that does not require any invasive intervention. Simultaneous visualization of the medial lung borders, with the presence of the pleural sliding sign and B-line artifacts, excludes the presence of PTX and allows differentiation between PM and PTX.

Consolidation refers to lung tissue changes from fluid-filled or collapsed alveoli. It appears on ultrasound when just beneath the pleural line and can result from inflammation, bleeding, obstruction, or external pressure. Atelectasis is consolidation due to pressure. Small subpleural consolidations are seen in severe RDS. Bronchograms, whether static or dynamic, may be seen in larger consolidations (35). In cases of meconium aspiration syndrome, consolidations may be irregularly distributed throughout the lungs, appearing adjacent to normal tissue or as an alveolar-interstitial pattern. Consolidation can present with bronchograms or show evidence of atelectasis resulting from a meconium plug (Supplementary Data—Video S6: Transversal linear probe ultrasound shows diffuse lung consolidations due to meconium aspiration syndrome. The patient is a term female (40 weeks, delivered by caesarean section) with birth weight 3,160 g and Apgar scores of 1, 4, 5, and 6.).

Acute Respiratory Distress Syndrome (ARDS) is characterised by a diffuse alveolar-interstitial pattern on imaging, accompanied by areas of consolidation with air bronchograms or evidence of atelectasis (7). Lung ultrasound findings for pneumonia include large consolidations with irregular margins and air bronchograms, pleural line abnormalities, interstitial syndrome, and pleural effusion (36). In neonates, lung ultrasound showed 96% sensitivity and 100% specificity for diagnosing pneumonia, though this is based on just two studies and may reflect selection bias (37). Newer research indicates that while lung ultrasound effectively assesses the presence and severity of neonatal pneumonia by measuring consolidation extent, it cannot identify aetiology (pathogens) in early disease stages (38). Inflammatory consolidation remains unchanged with posture or recruitment maneuvers and is associated with a bronchogram. In summary, analysis of lung consolidations in newborn ultrasound should consider the clinical context.

Lung ultrasound is the main method for diagnosing pleural effusion in newborns. Though uncommon (affecting less than 2.2% of NICU cases), pleural effusion can be life-threatening and has various causes. Most prenatal cases are linked to congenital chylothorax, severe heart disease with hydrops fetalis, or serious intrauterine infections. In the postnatal period, life-threatening effusions most commonly occur as a result of iatrogenic causes, such as thoracic surgical procedures or complications related to central venous catheterization, or may arise secondary to severe respiratory infections (39). The assessment for pleural fluid is an established element of point-of-care ultrasound (PoCUS) protocols during the evaluation of acute clinical deterioration in neonates within the NICU, as described in The Crashing Neonate section.

On ultrasound, pleural fluid is seen as a hypoechoic area between the parietal and visceral pleura. It may be free or loculated, localized or diffuse, and can appear homogeneous or with fine hyperechoic particles (“plankton sign”) (40). Quantification usually involves measuring the gap between the lung base and diaphragm or between the lateral lung surface and chest wall (see Figure 6). Large unilateral effusions may shift the mediastinum to the opposite side. The compressed lung often displays prominent B-lines or appears consolidated. Extensive effusions can clinically resemble pneumothorax.

Congenital diaphragmatic hernia (CDH) is the displacement of abdominal organs into the chest by a defect of the diaphragm. On the right side, the hernia typically contains a portion of the liver, which must be carefully differentiated from atelectatic lung tissue. The contents of the left-sided hernia are usually the stomach, intestines, and spleen. Intestines initially airless, quickly fill with air swallowed by the newborn—pleural line disruption, polycystic contours and peristaltic movements can be observed. Through the acoustic windows of the airless intestines, it is possible to visualize the vessels running in the mesentery drawn into the thorax. Additionally, by following the echotexture of the diaphragm, the margin of the defect can be delineated (Figure 7, Supplementary Data—Videos S7, S8).

Large defects result in hypoplasia of the compressed or both lungs and pulmonary hypertension of an irreversible nature. Small hernias in naturally occurring orifices (posterior-lateral—Bochdale's—more common, including more common on the left side, and anterior—Morgagni's) proceed without clinical symptoms (43).

Italian researchers modified the LUS scale to assess newborns with CDH, enabling physicians to tailor ventilation therapy around surgery. The adapted scale evaluates six areas per lung, providing objective data to determine optimal surgery timing and guide weaning from mechanical ventilation (44).

Postoperative lung assessment is commonly performed using lung ultrasound (LUS), which enables evaluation of lung expansion and detection of complications such as pneumothorax, pleural effusion, and consolidations indicative of pneumonia. The duration of abnormal LUS patterns may have prognostic value. For patients extubated within 7 days, the pattern typically returns to normal within 48 h following surgery. In contrast, patients who require prolonged ventilation often exhibit an interstitial or alveolar-interstitial pattern in both lungs for 2–3 weeks.

LUS may reveal features such as atelectatic cystic structures, irregular fluid-filled cysts, solid heterogeneous consolidations, emphysematous cysts, or abnormal vascular patterns—findings that can suggest the presence of CDH or congenital pulmonary malformation.

Congenital pulmonary airway malformation (CPAM), formerly known as congenital cystic adenomatoid malformation (CCAM), is the most common type of congenital lung malformation, accounting for approximately 30%–40% of cases (45). Usually unilateral, affects part of the lung, a lobe, or the entire lung. Non-respiratory lung tissue with undeveloped alveoli arises from uncontrolled hypertrophy of the terminal bronchioles. CPAM is usually solid in nature, with small air spaces or a cystic appearance. The cysts communicate with the surrounding parenchyma. Due to the concept of the formation of cystic lesions at different levels of the airways, there are now various histopathological types of CPAM (46–48). Type I is the most common form and is characterized by one or more large cysts (>2 cm in diameter) with a thick muscular wall. Type II lesions consist of uniform cysts measuring 0.5–1 cm in diameter, with thin walls. They are often associated with other congenital anomalies, including cardiac, renal, and diaphragmatic defects, and are linked to a poor prognosis. Type III represents a generalized adenomatoid overgrowth involving an entire lobe or multiple lobes. It appears as a solid mass containing small cysts (0.3–0.5 cm) and is considered the most severe form of CPAM due to its extensive nature, which can cause compression of adjacent structures, mediastinal shift, and even prenatal hydrops from cardiovascular compromise (46). Type IV consists of peripheral cystic lesions that histologically resemble type I well-differentiated pleuropulmonary blastoma (47).

Some forms of CPAM have communication with the bronchial tree, while others are associated with bronchial stenosis or atresia. Prenatal ultrasound diagnosis is possible. Rapid prenatal (at 20–26 weeks' gestation) development of the lesion may lead to impaired venous outflow, heart failure and generalized fetal hydrops. Fetal surgery is a potential therapeutic option in selected cases.

In postnatal lung ultrasound CPAM appears as cysts, emphysematous bullae, and glandular changes of a non-homogeneous consolidation nature. The vascularization of these changes most often comes from the pulmonary artery, venous drainage to the pulmonary venous system (Figure 8).

Bronchopulmonary sequestration (BPS), accounting for approximately 6% of congenital lung malformations, must be carefully differentiated from other atelectatic lesions (42). The sequestered segment is typically supplied by an aberrant artery arising from the thoracic or abdominal aorta, lacks communication with the airway, and does not participate in gas exchange. Depending on the type and extent of the lesion, systemic blood flow to the area may be increased.

Suspicion of BPS should be made prenatally. Ultrasound performed after birth can facilitate the identification of atelectatic lesions, which are most commonly located in the posterior basal segments, just above the diaphragm. Bronchopulmonary sequestration may present as intralobar or as extralobar, depending on its anatomical separation and pleural covering (Figure 9, Supplementary Data—Video S9).

Intrapulmonary sequestration (ILS) is located in the visceral pleura, most often supradiaphragmatic in the posterior field of the left lung. Ultrasound can detect a solid, cystic, cavernous, or cirrhotic lesion. The pleura is fibrotic. Arterial vascularization through atypical branches from the thoracic or abdominal aorta. Venous drainage into the pulmonary venous system. This type of defect is not associated with other defects.

Extrapulmonary sequestration (ELS) is surrounded by its own pleura, completely separated from healthy lung tissue. It is located supradiaphragmatically, in the diaphragm muscle, or subdiaphragmatically—in the retroperitoneal space in the area of the left adrenal gland. It requires differentiation from neuroblastoma (49). Arterial vascularization from the aorta, venous outflow to systemic veins or to the left atrium. This defect can be associated with other heart defects or pulmonary hypoplasia (47). In the case of changes involving the vascularization, it is most often necessary to perform angio CT of the chest. Sometimes congenital malformations may be of a hybrid nature, combining features of sequestration and CPAM. Foregut-derived bronchopulmonary malformations involve a sequestered segment of lung tissue that communicates with the gastrointestinal tract, typically the distal oesophagus or stomach. These lesions are more commonly located on the right side and are frequently associated with CDH, the VACTERL association, and clinical manifestations such as recurrent pneumonia, chronic cough, and respiratory distress (47).

Congenital lobar emphysema (CLE) accounts for 10% of congenital lung defects. It is a distention of a lobe or part of a lobe, most often the left upper lobe, caused by congenital bronchial stenosis. Symptoms appear after birth—increasing emphysema due to air trapping. If the lesion affects the entire lobe—it enlarges to such an extent that it causes displacement of the mediastinal structures to the opposite side, with impaired aeration of the compressed normal lung tissue with the risk of tension pneumothorax. LUS examination reveals mediastinum displacement, pulmonary hyperinflation (predominance of A-line)—displacement of the edges, decreased mobility of the lower edge, disappearance of the sliding sign or pneumothorax.

Atelectatic changes (BPS) require differentiation between inflammatory consolidations, neoplastic or vascular changes. Expansive lesions with mass effect (CPAM, CLE, CDH) cause displacement of the mediastinum to the opposite side, which is easily detected using ultrasound. These patients will most likely require surgical intervention (45).

LUS can help determine the indications for NIV and monitor its effectiveness. The underlying principle of lung imaging using ultrasound is that the more B-lines are present in the lung image, the worse the lung aeration. Based on this information, in a newborn with desaturation, it will be easier to select the group that will require respiratory support with positive end-expiratory pressure (PEEP). In subsequent steps, ultrasound will help with assessment of the effectiveness of NIV by differentiating patients with improved lung imaging (reduction in B-line profile) from those who benefit from escalation of respiratory support.

Since 2022, according to European guidelines for the care of preterm newborns, the LUS score is a factor that helps determine which preterm infants, currently on noninvasive respiratory support, should receive intratracheal surfactant (9, 13, 50, 51). Numoerous studies suggest LUS score can be used to predict the necessity of escalation to mechanical ventilation in preterm infants requiring respiratory support (51, 52–56).

During the management of a patient on MV, constant and accurate monitoring of their general condition, pulmonary status, and ventilation effectiveness is necessary. LUS is increasingly used as a complementary method alongside standard monitoring tools such as physical examination, blood gas analysis, and the oxygenation index. LUS performed in newborns receiving assisted ventilation allows for the assessment of lung aeration, including the identification of overdistension or areas of atelectasis. LUS is also known as an effective tool in assessment of lung recruitment maneuvers, which are performed as a rescue approach in critically ill neonates (16, 56–58). As a bedside, real-time, and safely repeatable examination, it enables monitoring of the effects of therapeutic interventions, such as changes in ventilator settings, endotracheal tube and patient positioning, or administration of mucolytic agents.

Another use of LUS has been reported that in patients with a particularly severe manifestation of respiratory failure in the course of acute respiratory distress syndrome (ARDS). Ultrasound enables the choice of appropriate ventilation pressures (PEEP), resulting in a reduction in the frequency of complications and shortening the duration of mechanical ventilation, better or as well as previously used clinical tools (59, 60).

Algorithms for extubation also incorporate lung ultrasound. In a hemodynamically stable patient, after sedation withdrawal, a pressure support breathing trial is performed through the endotracheal tube, and by assessing the degree of lung aeration in the following hours, the success of weaning from mechanical ventilation can be predicted (61). LUS score also appears to be helpful in predicting extubation failure, though its accuracy may be lower in extremely preterm infants (62, 63) To date, no studies have explored the use of LUS in patients on high frequency ventilation. From the authors' experience, some of the rules, such as the evaluation of lung aeration or atelectasis presence, can be transferred from those that are used for conventional ventilation.