Lung surfactants and antenatal corticosteroids: Nursing pharmacology

Lung surfactants are lipoproteins produced and secreted by type II pneumocytes lining the lung alveoli to keep them from collapsing when air is exhaled.

The production of surfactants typically begins at around week 26 of gestation, and reaches sufficient levels by week 35. So, preterm babies born before that don't produce enough lung surfactants.

As a consequence, their alveoli collapse, leading to neonatal respiratory distress syndrome. To prevent this, preterm babies are administered exogenous lung surfactants.

Commonly used exogenous lung surfactants include beractant, which is a bovine lung derivative; calfactant, which is a calf lung derivative; and poractant alfa, which is a porcine lung derivative.

Exogenous surfactants are usually administered directly into the newborn’s airways through an endotracheal, or ET tube, or via less invasive surfactant administration or LISA for short, such as nebulized surfactant preparations, laryngeal masks, and intratracheal instillation.

Once administered, lung surfactants form a film that coats the inner walls of the alveoli. This film decreases the surface tension, which helps maintain the alveolar shape by preventing the inner walls from sticking to each other and collapsing during expiration.

Now, before birth, corticosteroids like betamethasone and dexamethasone can be administered to promote fetal lung maturation. This is also known as antenatal corticosteroid therapy, and it is usually administered intramuscularly to pregnant clients at 24 to 33 weeks and 6 days of gestation who are expected to go into preterm labor.

Administration of antenatal corticosteroids reduces the risk of respiratory distress syndrome in premature babies. Also, it has been shown to have other benefits too, including a reduced risk of neonatal mortality; sepsis; intraventricular hemorrhage, or bleeding in the brain; and necrotizing enterocolitis, a serious intestinal condition affecting premature babies.

Once administered, antenatal corticosteroids travel from the client’s bloodstream to the fetus. Here, they stimulate the development of both type I and type II pneumocytes in the fetal alveoli, leading to alveolar development as well as an increased production of endogenous lung surfactant. This allows the alveoli to stay open, which improves gas exchange; moreover, the lungs become more compliant, meaning they are less stiff and easier to ventilate.

Now, both lung surfactants and antenatal corticosteroids are rarely associated with side effects. However, during administration of lung surfactants, transient bradycardia and oxygen desaturation may be observed.

In very low birth weight premature infants, surfactant administration may cause pulmonary hemorrhage. Lung surfactants are relatively contraindicated in infants with an existing pulmonary hemorrhage or with a congenital diaphragmatic hernia.

Finally, lung surfactants should not be administered in neonates with respiratory distress that’s not caused by lung immaturity.

On the other hand, fetal side effects of antenatal corticosteroids can include short-lived effects such as reduced fetal movements and fetal heart rate variability; while maternal side effects include increased risk of infections, a transient rise in serum glucose levels, and rarely, an increased risk of pulmonary edema.

Finally, antenatal corticosteroid therapy should not be administered to clients where immediate delivery is needed, as in cord prolapse, placental abruption, or chorioamnionitis.

Now, when caring for a pregnant client who is at risk for preterm labor, you will likely be administering antenatal corticosteroids as part of your client care.

Before administering the medication, confirm the estimated gestational age of the fetus and the results of prenatal gestational diabetes screening.

Then teach the client about the purpose of the steroid injection, potential side effects, and the monitoring you will be doing after administration such as glucose monitoring and respiratory assessments.

Administer the injection intramuscularly into a large muscle. The ventrogluteal injection site is common for this medication. Do not massage the injection site as this may damage the underlying muscle.

As you continue to monitor your client for preterm labor, monitor for side effects by assessing vital signs, auscultating lung sounds, and checking glucose levels.