Surfactant Replacement Therapy: An Overview

Pulmonary surfactant is a soap-like chemical synthesized by type II alveolar pneumocytes and is a mixture of phospholipids (predominantly dipalmitoylphosphatidylcholine), some other lipids and proteins. Its main functions include lowering the surface tension and maintaining the stability of alveoli. The first documented trial involving exogenous use of surfactants as a therapy was recorded in early 1970s using synthetically produced phospholipid mixtures once the chemical composition of surfactants was deciphered. Gradually there was a transition to the use of more natural sources. And animal derived surfactants like Surfactant TA, Beractant, Bovactant, Poractant Alfa etc. were then introduced. Recent works have highlighted the physiological importance of the surfactant-proteins and present day exogenous surfactants are mostly synthetic combinations incorporating the protein-part, either the whole surfactant proteins or peptides that act like surfactant proteins. Examples of this group include lucinactant, rSP-C surfactant, CHF 5633 etc. The commonest therapeutic indication of surfactants is in preterm infants suffering from Infant Respiratory Distress Syndrome (IRDS) or Hyaline Membrane Disease. Present guidelines recommend the use of early rescue therapy rather than prophylactic use of surfactant as it reduces acute pulmonary injury and the need for mechanical ventilation. Multiple-dose regimen has been found to be more effective than single dose surfactant therapy and minimum 100 mg/kg of surfactant is recommended. LISA is preferred method of delivering surfactant when baby is breathing spontaneously, on nasal CPAP or when intubation is not required for treatment. Exogenous surfactants form the mainstay of therapy in these infants born with deficiency of pulmonary surfactants which predisposes their lungs to collapse