A neonate born 45 minutes ago is evaluated in the neonatal intensive care unit for tachypnea. He was born at 33 weeks gestation via emergency cesarean delivery due to a non-reassuring fetal status. Rupture of membranes at delivery showed minimal clear amniotic fluid. Temperature is 37 C (98.6 F), pulse is 160/min, and respirations are 66/min. Pulse oximetry is 68% on room air. Examination shows nasal flaring and intercostal and subcostal retractions. Cardiac examination shows tachycardia with no rubs or murmurs. There are decreased breath sounds bilaterally. Chest radiograph reveals low lung volumes with diffuse, ground-glass opacities. Continuous positive airway pressure is provided, but the patient develops worsening respiratory status and is subsequently intubated. Which of the following is the most likely cause of this patient's clinical presentation?
Neonatal respiratory distress syndrome | |
Pathophysiology |
|
Clinical features |
|
Chest x-ray |
|
Management |
|
Prevention |
|
Complications |
|
This premature neonate most likely has respiratory distress syndrome (RDS), a disorder characterized by surfactant deficiency.
In general, around 20 weeks gestation, alveolar cells begin producing surfactant. Surfactant is primarily composed of phospholipids, which reduce alveolar surface tension in preparation for gas exchange after birth. The quantity and quality (ie, optimal phospholipid composition) of surfactant increase throughout gestation.
In a premature neonate, insufficient and immature surfactant results in increased alveolar surface tension and poorly compliant alveoli. The pressure required to keep the alveoli open upon expiration is therefore increased and ultimately results in alveolar collapse. Diffuse atelectasis leads to areas of the lung that are perfused but not ventilated (ie, ventilation/perfusion mismatch), resulting in hypoxia. Characteristic findings include increased work of breathing (eg, retractions, nasal flaring) minutes to hours after birth, decreased breath sounds, and low lung volumes with a ground-glass appearance on chest x-ray.
(Choice A) Air leakage into lung perivascular tissue describes pulmonary interstitial emphysema, which presents with worsening hypoxia in mechanically ventilated patients who require high pressures to maintain oxygenation. In contrast, this patient's respiratory distress began immediately after birth.
(Choice B) Meconium aspiration syndrome leads to respiratory distress due to bronchiolar obstruction and inflammation from particulate matter (ie, meconium). This patient's clear amniotic fluid makes this diagnosis unlikely. In addition, chest x-ray typically shows hyperinflated lungs and streaky, linear densities.
(Choice C) Defective surfactant metabolism and clearance can occur in pulmonary alveolar proteinosis, which can cause neonatal respiratory failure and ground-glass opacities on x-ray. However, this condition is exceedingly rare, making RDS far more likely, particularly in a premature neonate.
(Choice D) Bronchopulmonary dysplasia, characterized by airway injury and pulmonary fibrosis, is a chronic lung disease in neonates who require prolonged (>1 month) oxygen therapy. Although this patient is at risk of developing this condition, his age is inconsistent with the diagnosis.
(Choice E) Impaired clearance of alveolar fluid causes respiratory distress within hours of birth and occurs in transient tachypnea of the newborn. Unlike in this patient, chest x-ray shows fluid in the interlobar fissures, and severe hypoxia requiring invasive respiratory support is atypical.
Educational objective:
Neonatal respiratory distress syndrome presents immediately after birth with increased work of breathing and hypoxia in premature neonates. Pathogenesis involves surfactant deficiency, causing increased alveolar surface tension and diffuse atelectasis (seen on chest x-ray as diffuse ground-glass opacities).