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The surfactants

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Surfactant composition and action

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spacer Pulomary surfactant prevent collapse of the alveoli
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Surfactant is produced in the lungs of the unborn baby. At approximately week 20 the components start to appear however it is not until much later in pregnancy that the surfactant becomes mature enough to work correctly.

Surfactant is a complex substance containing phospholipids (fats) and four different types of surfactant proteins: hydrophilic (water-attracting) proteins SP-A and SP-D and the hydrophobic (water-repelling) proteins SP-B and SP-C. These latter proteins, SP-B and SP-C, are essential for the uniform spreading of the surfactant throughout the lung.

The main role of surfactant is to prevent collapse of the alveoli thereby reducing the effort needed to expand the lungs during inspiration (breathing in) and allow gas exchange to take place. Surfactant therefore helps breathing to be relatively effortless.

During expiration (breathing out) the lungs have a tendency to collapse, if they are allowed to do so then a much greater inspiratory effort is required to open them with the next breath. Surfactant prevents this by reducing surface tension throughout the lung; surface tension is the force present within the alveoli of the lungs that courses them to collapse and stick together during expiration. Surfactant forms a very thin film which covers the surface of the alveolar cells; the components of surfactant work together to reduce surface tension and therefore reduce the tendency of the alveoli to collapse during expiration. The lungs are less stiff (improved pulmonary compliance) and therefore reduced effort is needed to expand the lungs and making breathing easier.

The natural production of surfactant increases at approximately week 30 to 32 and babies born after the end of the 32nd week usually have sufficient surfactant to breath normally.


Surfactant Replacement Therapy

In the last 10 years several pharmaceutical companies, including Chiesi Farmaceutici have started producing surfactants that can be given to babies at risk of developing RDS, as either a preventative treatment or to treat babies that already have signs of RDS.

Surfactant is administered to babies directly to the lungs through a endotracheal tube (breathing tube) that is placed in the baby’s windpipe (also called trachea).

The amount and the number of doses required vary between surfactants and also between babies. Most babies respond relatively quickly to treatment however others may take a little longer , and a few have little or no response. Some babies who responded initially may relapse and need further surfactant treatment. Babies that respond well require less support from ventilators and lower additional oxygen support.

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