Surfactant Replacement Therapy: An Overview (2025)

Surfactant replacement therapy (SRT) has revolutionized the treatment and management of respiratory distress in newborns, particularly in premature infants. This therapy addresses a fundamental problem seen in neonatal care: the inability of underdeveloped lungs to produce sufficient surfactant.

By providing an overview of how SRT works, its importance, and the benefits it offers, we can better understand why it is considered a vital part of modern neonatal and respiratory care.

This article will explore the key concepts, mechanisms, and clinical applications of surfactant replacement therapy to enhance the comprehension of its role in respiratory health.

What is Surfactant?

Surfactant is a complex mixture of lipids and proteins secreted by the alveolar cells in the lungs, specifically by type II alveolar cells. Its primary function is to reduce the surface tension within the alveoli, the tiny air sacs in the lungs where gas exchange occurs.

By lowering the surface tension, surfactant prevents the alveoli from collapsing, especially during exhalation, and helps maintain lung stability and efficient gas exchange.

Surfactant plays a crucial role in respiratory health, as it allows the lungs to expand more easily with each breath, making breathing more efficient and less energy-consuming. Inadequate production or function of surfactant can lead to respiratory distress, such as in conditions like neonatal respiratory distress syndrome (RDS), which commonly affects premature infants whose lungs have not fully matured to produce sufficient surfactant.

What is Surfactant Replacement Therapy?

Surfactant replacement therapy (SRT) is a medical treatment primarily used for newborns, especially premature infants, who are unable to produce enough natural surfactant in their lungs.

This therapy involves administering artificial or animal-derived surfactant directly into the lungs to help reduce surface tension in the alveoli and improve lung function.

Purpose

In premature infants, the lungs may not have developed enough to produce adequate amounts of surfactant, leading to a condition called neonatal respiratory distress syndrome (RDS).

Without sufficient surfactant, the alveoli can collapse, making it difficult for the baby to breathe and for gas exchange to occur effectively. Surfactant replacement therapy helps prevent this collapse, improving oxygenation and reducing the work of breathing.

How it Works

Surfactant replacement therapy involves instilling a liquid form of surfactant into the infant’s trachea through a tube or catheter. This procedure is usually done while the baby is on a ventilator to assist breathing during the administration.

The surfactant spreads throughout the lungs, coating the alveoli and mimicking the natural surfactant’s effects, thereby reducing surface tension and improving lung compliance and oxygenation.

Types of Surfactant

• Animal-derived surfactants: These are extracted from bovine or porcine sources and are processed for medical use. Examples include beractant (Survanta) and poractant alfa (Curosurf).
• Synthetic surfactants: These are man-made and designed to replicate the properties of natural surfactant.

Benefits

• Improves lung function: Reduces surface tension, allowing the alveoli to stay open and maintain optimal gas exchange.
• Reduces mortality and complications: Significantly lowers the risk of complications associated with RDS, such as bronchopulmonary dysplasia and other lung injuries.
• Supports earlier weaning from ventilators: Helps infants breathe more effectively on their own, enabling faster weaning from mechanical ventilation.

Indications

• Neonatal Respiratory Distress Syndrome (NRDS): Premature infants with diagnosed or suspected neonatal RDS.
• Congenital surfactant deficiency: Infants with conditions that reduce surfactant production or function, such as some cases of congenital surfactant deficiency.

Note: Surfactant replacement therapy has been proven to be a life-saving intervention that greatly improves outcomes for infants with RDS, contributing to significant advancements in neonatal care.

Surfactant Replacement Therapy Practice Questions

1. What conditions does surfactant replacement therapy prevent and treat?
Infant Respiratory Distress Syndrome (IRDS) and Hyaline Membrane Disease (HMD).

2. What are the two techniques for administering surfactant?
Prophylactic and rescue administration.

3. Which surfactant administration technique is given to at-risk infants immediately after birth?
Prophylactic administration.

4. Which surfactant administration technique is given after an infant shows signs and symptoms of RDS?
Rescue administration.

5. What are six potential adverse effects of surfactant replacement therapy?
Pneumothorax, bradycardia, hypotension, hypoxemia, hemorrhage, and apnea.

6. How is surfactant replacement therapy administered?
It is instilled directly into the trachea, and the infant is positioned to help distribute the surfactant throughout the lungs using gravity.

7. What are three examples of surfactant drugs?
Calfactant, beractant, and poractant alfa.

8. What is another name for the surfactant drug calfactant?
Infasurf (bovine).

9. What is another name for the surfactant drug beractant?
Survanta (bovine).

10. What is another name for the surfactant drug poractant alfa?
Curosurf (porcine).

11. What is pulmonary surfactant?
A complex mixture of lipids and proteins that reduces surface tension in the alveoli and prevents their collapse during expiration.

12. Which surfactant proteins are crucial for innate immunity against inhaled pathogens?
SP-A and SP-D.

13. What is common in the pathophysiology of RDS, ARDS, and Meconium Aspiration Syndrome (MAS)?
Surfactant deficiency, dysfunction, or inactivation.

14. In which condition has exogenous surfactant replacement therapy been used successfully?
Neonatal RDS.

15. Surfactant replacement therapy is also being studied for which patient populations?
Patients with ARDS, asthma, and cystic fibrosis.

16. What is the most abundant component of surfactant?
Dipalmitoylphosphatidylcholine (DPPC).

17. In which condition is surfactant inactivation or dysfunction not typically described?
Congenital heart disease.

18. From which animals are natural surfactant preparations typically derived?
Pigs, cows, and calves.

19. Which alveolus requires higher pressure to inflate if surface tension is similar?
The smaller alveolus.

20. Which surfactant-associated protein deficiency is fatal in infancy without lung transplantation?
SP-B deficiency.

21. Which surfactant proteins play a critical role in infection defense?
SP-A and SP-D.

22. What is the most common complication of surfactant administration in preterm neonates?
Hypotension.

23. What are the benefits of surfactant replacement therapy in infants with RDS?
Reduced severity of RDS and decreased incidence of air leaks such as pneumothorax and pulmonary interstitial emphysema.

24. Which component of natural surfactant increases its efficacy compared to synthetic surfactants?
A higher percentage of DPPC.

25. What radiographic findings are typical in a child with RDS?
Atelectasis, air bronchograms, and a ground-glass pattern.

26. What does surfactant therapy aim to treat?
It aims to treat and reduce the severity of respiratory distress syndrome.

27. What are examples of surfactant therapy drugs?
Beractant, calfactant, and poractant alfa.

28. What is beractant’s function?
It decreases alveolar surface tension and stabilizes alveoli.

29. What is calfactant used for?
It is used for pre-ventilatory or post-ventilatory treatment and is derived from calf lung.

30. What is poractant alfa’s primary use?
It is used as a rescue treatment and is sourced from porcine lung surfactant.

31. How is surfactant administered?
It is given via an endotracheal tube (ETT). The infant’s head should be elevated, and suctioning should be avoided for 2 hours post-administration.

32. When should surfactant administration be paused or reconsidered?
If the infant becomes dusky, agitated, bradycardic, has an oxygen saturation below 95%, or CO2 levels drop below 30 mm Hg.

33. What is the primary function of surfactant?
To reduce surface tension in the alveoli and increase lung compliance, helping maintain proper physiological function in the lungs.

34. What composes pulmonary surfactant?
Surfactant is produced by Type II pneumocytes and is composed of 90% lipids and 10% proteins.

35. What is the most crucial component of surfactant?
Dipalmitoylphosphatidylcholine (DPPC).

36. What would happen if surfactant were absent?
Without surfactant, each breath would require significantly higher pressure (around -80 to -90 cmH₂O) to inflate the lungs, leading to rapid lung collapse during exhalation.

37. What should be administered to expectant mothers at risk of preterm delivery between 24 and 34 weeks of gestation?
Systemic corticosteroids should be given to help accelerate fetal lung maturity.

38. How is lung maturity determined?
By measuring the levels of phospholipids in the amniotic fluid.

39. What is the most reliable indicator of lung maturity?
The presence of phosphatidylglycerol (PG) — PG and lecithin levels increase, while sphingomyelin levels decrease as the lungs mature.

40. What are the benefits of administering prophylactic surfactant within the first 15 minutes of birth to preterm infants?
It decreases mortality rates, reduces the risk of pneumothorax, and lowers the chance of developing interstitial emphysema.

41. What is the initial dose and method of surfactant delivery?
A dose of 75-100 mL/kg is given through the ETT as quickly as possible, with the infant being turned to assist distribution.

42. What should be monitored during surfactant administration?
Heart rate, oxygenation (watching for cyanosis, bradycardia, reflux, airway obstruction), and the presence of surfactant in the ETT.

43. What are examples of synthetic surfactants?
Older drugs like EXOSURF (no longer marketed), PUMACTANT, and SURFAXIN.

44. What are examples of modified natural surfactants?
Survanta, Infasurf, and Curosurf.

45. What can inactivate surfactant?
Pulmonary hemorrhage, meconium aspiration syndrome, and conditions like pneumonia and sepsis.

46. What are findings related to surfactant use in various conditions?
Limited benefit in congenital diaphragmatic hernia, potential benefit in extracorporeal membrane oxygenation (ECMO), mixed results in ARDS, and little evidence of benefit in viral bronchiolitis, asthma, and cystic fibrosis.

47. What is the role of surfactant in the alveoli?
It helps prevent alveolar collapse by maintaining surface tension.

48. When should surfactant be administered to be most effective?
Within the first hour of birth and ideally before the second hour.

49. What is the typical method of surfactant administration?
It is usually administered through an endotracheal tube (ETT).

50. How frequently can surfactant be administered?
Up to four doses can be given within a 24-hour period.

51. How can you confirm that the lungs are open after surfactant administration?
A chest X-ray is used for confirmation.

52. What additional support might be needed alongside surfactant therapy?
A CPAP machine or intubation may be required.

53. What is the composition of surfactant?
It is composed of approximately 95% phospholipids and 5% proteins.

54. Where is surfactant produced and stored?
It is produced and stored in Type II alveolar cells, specifically within electron-dense structures known as lamellar bodies.

55. What is the non-polar tail of phospholipids, and what is its origin?
The non-polar tail consists of carbon chains up to 18 atoms long, derived from glucose or glycerol.

56. What are examples of polar phospholipid head groups?
Choline, inositol, serine, glycerol, and ethanolamine.

57. What proteins are found in surfactant?
SP-A, SP-B, SP-C, and SP-D.

58. What roles do SP-A and SP-D play in surfactant?
They are involved in regulation and host defense and are large hydrophilic proteins.

59. What are the roles of SP-B and SP-C?
They are essential for the formation and stabilization of the phospholipid monolayer and are small, lipophilic proteins.

60. How is the surfactant monolayer formed?
In lamellar bodies, the monolayer is formed after being broken down into tubular myelin, a process requiring SP-A, SP-B, and calcium ions.

61. What is the turnover rate of surfactant phospholipids?
The turnover rate ranges from 3 to 11 hours.

62. What happens to phospholipids before degradation?
They are taken up by Type II cells and transported to the ciliated airways due to surface tension gradients.

63. What degrades surfactant phospholipids?
Extracellular enzymatic activity, including the action of macrophages.

64. What occurs after phospholipid degradation?
Macrophages phagocytize the breakdown products, and epithelial cells reabsorb them into the lymphatic system or bloodstream.

65. How does surfactant function in reducing surface tension?
Phospholipids in the surfactant layer do not attract one another, thereby lowering surface tension and the intermolecular forces between water molecules.

66. What is lung compliance?
It is defined as the ability of the lung to distend per unit change in pressure.

67. What are the primary functions of surfactant?
Maintaining fluid balance, host defense, and lung compliance. It also reduces the formation of liquid plugs, lowers adhesion, supports hydration, and enhances mucus rheology.

68. How does surfactant affect fluid balance?
It reduces the tendency for fluid to be drawn into the airspaces.

69. How does surfactant maintain fluid balance in the lungs?
The rigid structure of the alveoli tends to collapse, creating a slight negative pressure around them, which in turn establishes a hydrostatic pressure gradient that draws fluid into the lung.

70. What role does surfactant play in host defense?
It assists in the movement of particulate matter toward ciliated regions through surface tension gradients.

71. How do surfactant proteins contribute to host defense?
SP-A and SP-D bind to pathogens and promote macrophage activity as part of the immune response.

72. In what condition is surfactant crucial for premature infants?
Neonatal Respiratory Distress Syndrome (NRDS).

73. What infectious diseases are linked to surfactant function?
Pneumonia, HIV-related pneumocystis carinii pneumonia, and pulmonary edema.

74. Which obstructive lung diseases are associated with surfactant dysfunction?
Asthma, bronchiolitis, and COPD.

75. What congenital diseases involve surfactant abnormalities?
Cystic fibrosis and surfactant protein B deficiency, the latter of which can be fatal.

76. What non-specific respiratory condition involves surfactant dysfunction?
Acute Respiratory Distress Syndrome (ARDS)

77. What occurs during Neonatal Respiratory Distress Syndrome (NRDS)?
High pressure but low lung volume upon initial breaths at birth; hyaline membrane disease damages the alveolar membranes.

78. What was used in the 1970s to manage NRDS?
Specialized neonatal ventilators

79. What significant advancement was made in the treatment of NRDS?
The introduction of antenatal steroid therapy.

80. What treatment was introduced in the 1990s for NRDS?
Exogenous pulmonary surfactant therapy.

81. What is the brand name for calfactant?
Infasurf

82. What is the brand name for poractant alfa?
Curosurf

83. What is the brand name for beractant?
Survanta

84. Which surfactant is classified as a modified natural surfactant?
Beractant

85. Which surfactant is derived from calf lungs?
Calfactant

86. Which surfactant is derived from porcine lungs?
Poractant alfa

87. Which surfactant is derived from bovine sources?
Beractant

88. Which surfactant is not approved for prophylactic use?
Poractant alfa

89. At what gestational age can calfactant be used for prophylaxis?
For infants less than 29 weeks of gestation.

90. At what weight can beractant be used for prophylaxis?
For infants weighing up to 1,250 grams.

91. What is the recommended dose for calfactant?
3 mL/kg

92. What is the recommended dose for poractant alfa?
2.5 mL/kg

93. What is the recommended dose for beractant?
4 mL/kg

94. Which surfactant should be administered within 30 minutes of birth?
Calfactant

95. Which surfactant should be administered within 15 minutes of birth?
Beractant

96. Which surfactant has an age restriction for rescue therapy?
Calfactant (must be used in infants ≤72 hours of age).

97. Which surfactant can be given through the side port of an ETT adapter while using a ventilator?
Calfactant

98. Which surfactant does not require warming to room temperature?
Calfactant

99. Which surfactant may need gentle swirling of the vial before administration?
Calfactant

100. Which surfactant is known to be the most cost-effective?
Calfactant

Final Thoughts

Surfactant replacement therapy represents a significant advancement in the treatment of respiratory distress, offering a lifeline to infants whose immature lungs struggle to function without assistance.

By reducing surface tension within the alveoli, SRT improves lung compliance, enhances oxygenation, and reduces the risk of complications associated with respiratory distress.

Understanding how this therapy works and the benefits it provides can deepen our appreciation of its impact on neonatal care and inspire continued advancements in respiratory treatment practices.