Meconium Aspiration Syndrome (MAS) (for Parents)

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Meconium Aspiration Syndrome is a serious condition in newborns that can cause severe respiratory distress. As a Respiratory Therapist, this is a topic that you must be familiar with.

This study guide was written to (hopefully) make the learning process easier for you. It contains practice questions for your benefit as well. So if you’re ready, let’s get started.


 Meconium Aspiration Syndrome

What is Meconium Aspiration Syndrome?

Meconium Aspiration Syndrome is a condition in a newborn that causes respiratory distress when meconium is aspirated into the lungs.

Meconium is a term for fecal matter that is passed by the fetus while in the womb and often occurs due to a lack of oxygen.

Pathophysiology of Meconium Aspiration Syndrome

Hypoxia during utero leads to gut paralysis that relaxes the anal sphincter and meconium is passed. Then, the hypoxic fetus gasps with thick meconium being inhaled into the bronchial tree.

Meconium allows the air in but inhibits the exhalation of carbon dioxide which can cause a pneumothorax. Meconium acts as an irritant, causing pneumonitis and infection which results in an increased body temperature.

Meconium also breaks down surfactant and causes impaired gas exchange where blood is shunted away from fetal circulation due to increased pulmonary resistance.

When Does Meconium Aspiration Syndrome Occur?

It is most common in full-term and post-date infants related to fetal distress which leads to a hypoxia-induced vagal response causing the passage of meconium.

Meconium is aspirated during gasping in utero and/or perinatally, causing airway obstruction by ball-valve mechanism resulting in simultaneous atelectasis and overexpansion which potentially leads to air leaks.

Chemical inflammation (pneumonitis) causes alveolar collapse and parenchymal damage. The inhibition of surfactant causes alveolar collapse and decreased lung compliance.

Persistent pulmonary hypertension of the newborn can occur as a result of hypoxia-induced pulmonary artery vasoconstriction and failure to transition to postnatal circulation.

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