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Pediatrics

Neonatal respiratory distress - diagnosis guide


If your newborn patient is experiencing difficulty breathing, here are the most common explanations: respiratory distress syndrome (RDS, transient tachypnea of the newborn (TTN), meconium aspiration syndrome (MAS), and neonatal pneumonia.

Mechanism of pathology

  • RDS - Baby is born preterm (<37 wks) with insufficient surfactant, so the lungs can't expand fully. Surfactant production revs up at ~34 wks; babies <34 weeks are at very high risk for RDS.
  • TTN - Baby doesn't get the benefit of a full vaginal squeeze at delivery, delaying clearance of fetal lung fluid, creating transient pulmonary edema.
  • MAS - Aspiration of meconium-stained amniotic fluid into the airways, leading to obstruction, chemical pneumonitis, and risk of air trapping or lung injury.
  • Neonatal pneumonia - Perinatal infection, often bacterial

Diagnosing without imaging

Even without the chest radiograph, you can make a good guess:

  1. Preterm (<37 weeks) infant, particularly <34 weeks - RDS
  2. C-section delivery or fast vaginal delivery with mild respiratory distress that resolves in 72 hrs - TTN
  3. Meconium-stained amniotic fluid plus peripartum fetal distress (increases risk of gasping/aspirating meconium in utero) with severe respiratory distress > 72 hrs after delivery - MAS. Note only 5% of meconium stained have MAS, so meconium staining does not automatically exclude other possibilities.
  4. Fever, elevated WBC - neonatal pneumonia
    Other risk factors: prolonged rupture of membranes (water breaks > 18 hrs before delivery), positive maternal rectovaginal swab for group B strep (tested before delivery), maternal fever or chorioamnionitis

Adding imaging clues

Chest radiography can help confirm your diagnosis. Below are the ideal characteristics, but in reality, the radiographic appearance of RDS, TTN, MAS, and neonatal pneumonia overlap with each other.

RDS

  • Lung Volume: low
  • Opacity: diffuse bilateral groundglass +/- air bronchograms
  • Also check for:
    • Is the patient intubated? Check closely for pneumothorax associated with barotrauma from the ventilator pushing against stiff lung.
    • Did your surfactant treatment reach all of the lungs? Check post-treatment radiographs to look for parts of lung that remain with low volume because surfactant didn't reach there.

TTN

  • Lung Volume: normal
  • Opacity: Looks like pulmonary vascular congestion- perihilar streaking, fluid in minor fissure, +/- mild pleural effusions. More severe TTN may have perihilar-predominant alveolar airspace involvement.
  • Also check for:
    • Did the TTN resolve in 72 hours (3 days) from delivery? If not, you might be dealing with something different. Resolution <3 days does not exclude MAS.
    • Does the patient require intubation? If so, this is probably not TTN, which tends to require supportive oxygen, but not intubation.

Meconium Aspiration Syndrome

  • Lung Volume: increased (hyperinflation)
  • Opacity: patchy asymmetric opacities (atelectasis and consolidation), +/- air trapping, possible pneumothorax or pneumomediastinum. Pleural effusions may be present. Slow (>3 day) resolution of symptoms favors MAS, but milder or treated MAS may resolve in shorter time frame.

Neonatal Pneumonia

  • Lung Volume: low or normal
  • Opacity: focal consolidation

Term infants with meconium staining and respiratory distress

If your patient is a term infant (>=37 weeks) in respiratory distress with meconium-stained amniotic fluid, they don't necessarily have MAS, and you should consider TTN and neonatal pneumonia as possibilities.

Note: if your patient is a preterm (<37 weeks) infant, stop reading this section.

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Only 5% of deliveries with meconium stained amniotic fluid results in neonatal MAS.

Use this qualitative point system to differentiate MAS, TTN, and neonatal pneumonia, as a first approximation.

Features that favor some possibilities, but eliminate none

  • Pneumothorax - 2 points for MAS. Affects 20-40% of MAS.
  • Severe respiratory distress requiring intubation - 2 points for MAS. TTN does not typically require intubation.
  • High lung volume - 1 point for MAS and neonatal pneumonia. Can occur in some TTN.
  • Peripartum fetal distress - 1 point for MAS. increases risk of MAS, does not exclude TTN or neonatal pneumonia.
  • Alveolar airspace opacities - 1 point for MAS and neonatal pneumonia. TTN in severe cases can produce diffuse or perihilar predominant alveolar airspace opacities.
  • C-section - 1 point for TTN. Does not exclude the others.
  • Pleural effusions and fluid in minor fissure - 1 point for TTN. Can occur in MAS.

Features that eliminate some possibilities

  • Prolonged duration > 3 days - 1 point for MAS, 1 point for neonatal pneumonia. Remove TTN from your differential.
  • No alveolar airspace opacities - 1 point for TTN. Mild MAS may have only streaky perihilar airspace opacities without alveolar airspace opacities. Remove neonatal pneumonia from your differential.
  • No meconium staining - remove MAS from your differential.
  • Short duration < 3 days without antibiotics - 1 point for TTN. Can occur in mild or treated MAS. Remove neonatal pneumonia from your differential.

Keep an open mind

Are there other causes of neonatal respiratory distress? Of course. Keep your mind open to other possibilities if none of these descriptions fit your clinical presentation (history, physical exam, labs) or imaging, or if your patient isn't responding to your treatment directed at one of these diagnoses.