Synonym: hyaline membrane disease

Infant respiratory distress syndrome (IRDS) is caused by the inadequate production of surfactant in the lungs. Surfactant is normally produced by type II pneumocytes and has the property of lowering surface tension. Most alveolar surfactant is produced after 30 weeks' gestation. Inadequate surfactant production causes air sacs to collapse on expiration and greatly increases the energy required for breathing. The development of interstitial oedema makes the lung even less compliant. This leads to hypoxia and retention of carbon dioxide. Right-to-left shunting may be severe and occurs through collapsed lung (intrapulmonary) or, if pulmonary hypertension is severe, across the ductus arteriosus and the foramen ovale (extrapulmonary).

Epidemiology

• The incidence and severity are related inversely to the gestational age of the infant.
• Affects approximately one half of infants born at 28-32 weeks' gestation. It may rarely occur at term.
• The incidence of IRDS decreases with:¹
  • The use of antenatal steroids
  • Pregnancy-induced or chronic maternal hypertension
  • Prolonged rupture of membranes
  • Maternal narcotic addiction

Risk factors

• Premature delivery
• Male infants
• Infants delivered via Caesarean section without maternal labour
• Hypothermia
• Perinatal asphyxia
• Maternal diabetes
• Multiple pregnancy
• Family history of IRDS

Secondary surfactant deficiency may occur in infants as a result of:¹

• Intrapartum asphyxia
• Pulmonary infection, e.g. group B beta-haemolytic streptococcal pneumonia
• Pulmonary haemorrhage
• Meconium aspiration pneumonia
• Oxygen toxicity along with pressure or volume trauma to the lungs
• Congenital diaphragmatic hernia and pulmonary hypoplasia

Presentation

• Usually preterm delivery.
• Presents very soon after birth with respiratory distress: tachypnoea, expiratory grunting, subcostal and intercostal retractions, diminished breath sounds, cyanosis and nasal flaring.
• May rapidly progress to fatigue, apnoea and hypoxia.

Differential diagnosis

Other causes of respiratory distress in neonates:

• Pulmonary air leaks (e.g., pneumothorax, interstitial emphysema, pneumomediastinum, pneumopericardium). In premature infants, these may occur from excessive positive pressure ventilation, or they may be spontaneous.
• Any infection may cause respiratory distress and may co-exist with IRDS; rapid diagnosis and treatment of any infection is essential.
• Pneumonia is often due to group B beta haemolytic streptococci and often coexists with IRDS.
• Aspiration of amniotic fluid, blood, or meconium may occur. It is usually seen in term or postmature infants.
• Transient tachypnoea of the newborn usually occurs in term or near-term infants and usually after caesarean delivery.
• Congenital anomalies of the lungs (e.g., diaphragmatic hernia, chylothorax, lobar emphysema, bronchogenic cyst, pulmonary sequestration).
• Congenital heart anomalies.
• Primary persistent pulmonary hypertension of the newborn (persistent fetal circulation).
• Metabolic problems (e.g. hypothermia, hypoglycaemia).
• Haematological problems (e.g. anaemia, polycythaemia).

Investigations

• Blood gases: respiratory and metabolic acidosis along with hypoxia. Metabolic acidosis results from poor tissue perfusion.
• Pulse oximetry is used as a non-invasive tool to monitor oxygen saturation, which should be maintained at 90-95%.
• Chest X-ray.
• Monitor full blood count, electrolytes, glucose, renal and liver function.
• Echocardiogram: diagnosing patent ductus arteriosus (PDA), determine the direction and degree of shunting, making the diagnosis of pulmonary hypertension and excluding structural heart disease.
• Cultures to rule out sepsis.

Management²

• Surfactant replacement therapy is given via an endotracheal tube. It is associated with a 40% reduction in mortality. It is more effective when given prophylactically at delivery rather than rescue, when symptoms develop.^3,4
• Oxygen:
  • Oxygen via a hood is still used for treating infants with mild IRDS.
  • Continuous positive airway pressure (CPAP) keeps the alveoli open at the end of expiration. CPAP may be administered via an endotracheal tube, nasal prongs, or nasopharyngeal tubes. CPAP is an adjunct therapy following surfactant administration, if prolonged positive pressure ventilation is not required. CPAP may be used following extubation in individuals with IRDS to prevent atelectasis and apnoea.
  • Assisted ventilation at fast rates (more than 40 breaths per minute) improves outcome more than at lower rates. Ventilators that are triggered and integrate with the baby's respiratory effort, high-frequency oscillatory ventilation and high-frequency jet ventilation are claimed to be more effective and safer but there is currently no major evidence of clinical benefit.
• Supportive therapy includes the following:
  • Gentle and minimal handling.
  • Temperature regulation: prevent hypothermia.
  • Fluids, metabolism and nutrition: closely monitor and maintain blood glucose, electrolytes, acid balance, calcium, phosphorous, renal function and hydration.
  • Once the infant is stable, intravenous nutrition with amino acids and lipid.
  • After the respiratory status is stable, initiate small volume gastric feeds (preferably breast milk) via a tube initially to stimulate gut development.
  • Circulation and anaemia: monitor heart rate, peripheral perfusion and blood pressure. Blood or volume expanders may be required.
  • Antibiotics: start antibiotics in all infants who present with respiratory distress at birth, after obtaining blood cultures. Discontinue antibiotics after three to five days if blood cultures are negative.
  • Support of parents and family: keep the parents well informed. Encourage parents to visit frequently and stay with their baby.

Complications

• Acute complications include the following:
  • Complications related to procedures, e.g. trauma to vocal cords from tracheal intubation; infection, embolism or thrombosis from venous or arterial catheterisation.
  • Alveolar rupture: pneumothorax, pneumomediastinum, pneumopericardium, interstitial emphysema.
  • Intracranial haemorrhage: the risk is increased in those who require mechanical ventilation.
  • PDA, with increasing left-to-right shunt, especially in infants weaned rapidly after surfactant therapy.
  • Persistent pulmonary hypertension.
  • Occurrence of pulmonary haemorrhage increases in very premature infants, especially following surfactant therapy.
  • Hospital acquired infection.
  • Necrotising enterocolitis and/or gastrointestinal perforation.
  • Apnoea of prematurity is common in immature infants, and its incidence has increased with surfactant therapy, possibly due to early extubation.
• Chronic complications include the following:
  • Chronic lung disease (bronchopulmonary dysplasia) is defined either as oxygen requirement at a corrected gestational age of 36 weeks or beyond the 28th day of life. It is due to lung injury from mechanical ventilation and the risk increases with decreasing gestational age, small for dates, severity of respiratory distress syndrome and duration of mechanical ventilation.
  • Retinopathy of prematurity: infants with IRDS and PaO₂ greater than 100 mmHg are at a greater risk.
  • Neurological impairment is related to the gestational age, the extent of intracranial pathology, the presence of hypoxia, and the presence of infections. They may develop a specific learning disability and behaviour problems.
  • Hearing impairment and visual handicap may further compromise development.

Prognosis

• The outcome has improved in recent years with the increased use of antenatal steroids to improve pulmonary maturity, early postnatal surfactant therapy to replace surfactant deficiency and gentler techniques of ventilation to minimise damage to the immature lungs.
• The prognosis is much better for babies weighing over 1500g.

Prevention

• Antenatal corticosteroids (dexamethasone) accelerate fetal surfactant production and lung maturation. They have been shown to reduce IRDS, intraventricular haemorrhage and mortality by 40%.⁵
• Delaying premature birth. Tocolytics, e.g. atosiban, nifedipine or ritodrine, may delay delivery by 48 hours and therefore enable time for antenatal corticosteroids to be given.
• Good control of maternal diabetes.
• Avoid hypothermia in the neonate.