Surfactant Replacement Therapy

Surfactant replacement therapy gives exogenous pulmonary surfactant into the airway of preterm infants with respiratory distress syndrome. It lowers alveolar surface tension, prevents atelectasis, reduces air leak and improves survival without bronchopulmonary dysplasia. It is a neonatal intensive care treatment given by trained staff.

Mechanism. Surfactant contains dipalmitoylphosphatidylcholine, phosphatidylglycerol and surfactant proteins B and C. It forms a film at the air liquid interface that keeps alveoli open at end expiration, improving compliance and functional residual capacity.

Classification. Natural animal-derived preparations are poractant alfa (porcine), beractant (bovine) and calfactant (bovine). Synthetic preparations have limited availability. Natural preparations are preferred because oxygen weaning is faster and air leak is less frequent.

Pharmacokinetics. Instilled surfactant spreads rapidly through the airways, is taken up and recycled by type II cells and is cleared by macrophages over hours to days. No dose adjustment is needed for kidney or liver function.

Differences. Poractant alfa at the higher first dose lowers the need for repeat doses and gives lower mortality than beractant in comparisons. Use the product that is available and follow its label for dose and interval.

Delivery. Instillation through an endotracheal tube in a ventilated infant, brief intubation and extubation, or less invasive administration through a thin catheter in a spontaneously breathing infant on CPAP.

Rescue treatment. Give early to infants with respiratory distress syndrome on CPAP of at least 6 cmH2O who need FiO2 over 0.30, preferably within 2 hours of birth. Diagnosis rests on grunting, retractions, tachypnoea and a chest radiograph showing ground glass change with air bronchograms.

Prophylaxis. Infants who need intubation for stabilisation at birth, mainly gestation under 26 weeks, within 15 minutes of birth. Many units use a threshold of under 28 weeks.

Repeat dosing. Give a further dose if the infant remains ventilated with FiO2 over 0.30 and high airway pressure after 6 to 12 hours, depending on the product, to a maximum of 3 doses in total.

Other uses. Meconium aspiration with severe hypoxaemia and pulmonary haemorrhage, as a specialist decision with limited evidence. It is not used in acute respiratory distress syndrome in adults.

Adjuncts. Antenatal corticosteroids when delivery is expected within 7 days at 24 to 34 weeks: betamethasone 12 mg intramuscularly, 2 doses 24 hours apart. They lower respiratory distress syndrome, death and need for surfactant. Early CPAP and oxygen titration also reduce injury.

Region. Surfactant is costly and often unavailable in East African neonatal units. Antenatal corticosteroids, early bubble CPAP, careful oxygen titration and transfer to a centre with surfactant are the main measures where supply is absent.

Adverse effects. Transient bradycardia, hypoxia, hypotension and tube blockage during instillation, with reflux of surfactant up the tube. Pulmonary haemorrhage occurs in about 1 to 5 percent. Pneumothorax can follow the rapid change in compliance, and apnoea can occur during catheter administration.

Handling. Store refrigerated at 2 to 8 degrees C, protect from light and do not shake. Bring to the temperature stated on the label before use. Calculate the dose by birth weight and discard opened vials.

After the dose. Wean FiO2 and ventilator pressures promptly to prevent hyperoxic injury and pneumothorax.

Interactions. None of pharmacological importance.

Monitoring. Oxygen saturation, heart rate, blood pressure, chest movement, blood gas, FiO2 and ventilator pressures after dosing, and a chest radiograph. Cranial ultrasound is routine in preterm infants.

Special groups. Preterm infants are the main group. Term infants with meconium aspiration or severe pneumonia are treated by specialists. No renal or hepatic adjustment.

Referral and escalation. No improvement after 2 doses, or persistent FiO2 over 0.40 with high pressures, suggests pneumothorax, patent ductus arteriosus, sepsis, pulmonary hypoplasia or a surfactant protein deficiency and needs senior neonatal review. Sudden deterioration after a dose needs checking of tube position and blockage and exclusion of pneumothorax.