Surfactant composition and action

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 composition and action

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.

By Gestational Age Description
Term A baby that is born between 37 and 41 weeks
Premature A baby that is born between 37 and 28 weeks
Extremely Premature A baby that is born before 28 weeks
By Birth Weight
Low Birth Weight A baby weighing between 2,500g and 1,500g
Very Low Birth Weight A baby weighing between 1,500g and 1,000g
Extremely Low Birth Weight A baby weighing less than 1,000g

Premature babies have many special needs so, after delivery, many of them are taken care of in a neonatal intensive care unit (NICU). The NICU is an ideal setting for the baby providing warmth, nutrition, and protection while the baby grows and develops.

Premature babies have a high risk of developing illnesses such as breathing (respiratory) difficulties. In particular extremely premature babies may have respiratory difficulties due to the fact that the lungs are immature. These babies may develop a serious disease called Respiratory Distress Syndrome (RDS). In the following chapters you will find some useful information regarding the baby’s lungs and circulation, RDS and the role of surfactant is this disease.

It is important to note that nowadays due to many recent advances in neonatology, more than 90% of premature infants who weigh 1000g or more can survive, and even infants weighing as little as 500-700g have now a relatively good chance of survival, even though they may develop more complications.

NICU - Neonatal Intensive Care Unit FAQ Abbreviations Suggested Reading
Last updated: 27/05/2015

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