Introduction
Respiratory distress is a common and potentially life-threatening condition in neonates, especially in the first 72 hours of life. Early diagnosis of the underlying cause is crucial for prompt management and reduction of morbidity and mortality.
While chest radiography remains the initial imaging modality, neonatal lung ultrasound (LUS) has emerged as a valuable bedside, radiation-free tool, particularly in NICU settings. Ultrasound is also useful in evaluating pleural, diaphragmatic, and cardiac causes of respiratory distress.
Advantages of Neonatal USG
- Bedside, portable, and repeatable
- No ionizing radiation
- Real-time dynamic assessment
- High sensitivity for pleural and lung pathologies
- Useful in unstable neonates who cannot be shifted
Ultrasound Technique
Equipment
- High-frequency linear probe (7.5–12 MHz)
- Curvilinear probe for deeper structures if needed
Scanning Areas
- Anterior, lateral, and posterior chest walls
- Intercostal approach in supine or lateral decubitus position
Normal Lung USG Appearance
- Pleural line: Smooth, hyperechoic line with lung sliding
- A-lines: Horizontal reverberation artifacts (normal aeration)
- No consolidation or pleural effusion
Common Causes of Neonatal Respiratory Distress & USG Findings
1. Respiratory Distress Syndrome (RDS / Hyaline Membrane Disease)
Etiology: Surfactant deficiency (common in preterm neonates)
Ultrasound Findings:
- Diffuse bilateral B-lines (white lung appearance)
- Thickened, irregular pleural line
- Reduced or absent A-lines
- No spared normal lung areas
Significance:
- Correlates well with severity
- Useful for monitoring response to surfactant therapy
2. Transient Tachypnea of the Newborn (TTN)
Etiology: Delayed clearance of fetal lung fluid
Ultrasound Findings:
- Double lung point sign (pathognomonic)
- Upper lung: A-lines (normal aeration)
- Lower lung: B-lines (interstitial fluid)
- Normal lung sliding
Differentiation from RDS:
- TTN has focal involvement with spared areas
- RDS shows diffuse bilateral involvement
3. Meconium Aspiration Syndrome (MAS)
Etiology: Aspiration of meconium-stained amniotic fluid
Ultrasound Findings:
- Heterogeneous lung consolidation
- Irregular pleural line
- Areas of atelectasis alternating with normal lung
- Possible pleural effusion
4. Neonatal Pneumonia
Etiology: Bacterial or viral infection
Ultrasound Findings:
- Lung consolidation with air bronchograms
- Irregular, thickened pleural line
- Focal or multifocal involvement
- Pleural effusion may be present
Role of USG:
- Helps differentiate pneumonia from RDS and TTN
5. Pneumothorax
Etiology: Air leak syndrome, often in ventilated neonates
Ultrasound Findings:
- Absence of lung sliding
- Absence of B-lines
- Presence of lung point sign (diagnostic)
- Prominent A-lines
Importance:
- USG is more sensitive than chest X-ray in early detection
6. Pleural Effusion
Ultrasound Findings:
- Anechoic or hypoechoic fluid collection
- Lung floating or compressed
- Septations if infected (empyema)
7. Congenital Diaphragmatic Hernia (CDH)
Ultrasound Findings:
- Absent lung tissue on affected side
- Bowel loops or solid abdominal organs in thorax
- Mediastinal shift
- Abnormal diaphragmatic contour
8. Cardiac Causes (Screening Role of USG)
Though echocardiography is definitive, bedside USG may suggest:
- Cardiomegaly
- Pleural effusion
- Signs of heart failure
Comparison with Chest X-Ray
| Feature | Chest X-Ray | Lung Ultrasound |
|---|---|---|
| Radiation | Yes | No |
| Pneumothorax | Moderate sensitivity | High sensitivity |
| Pleural effusion | Moderate | Excellent |
| Monitoring | Limited | Ideal |
Clinical Applications of Neonatal Lung USG
- Early diagnosis of cause of respiratory distress
- Differentiation between RDS and TTN
- Monitoring response to surfactant therapy
- Detection of complications (pneumothorax, effusion)
- Reducing need for repeated X-rays
Limitations of Neonatal USG
- Operator dependent
- Limited evaluation of deep lung parenchyma
- Does not replace chest X-ray or CT in all cases
Summary / Key Points
- Neonatal lung ultrasound is a safe, rapid, and effective bedside tool in respiratory distress.
- It is particularly useful in differentiating RDS, TTN, pneumonia, and pneumothorax.
- USG complements chest radiography and reduces radiation exposure in NICU patients.
- Increasingly becoming part of routine neonatal critical care imaging.
Conclusion
Neonatal ultrasound plays an increasingly important role in the evaluation of respiratory distress. With proper technique and interpretation, it provides accurate, real-time information, improves patient care, and minimizes radiation exposure in this vulnerable population.
