Meconium aspiration syndrome is a serious condition that is caused by aspiration of amniotic fluid containing meconium, leading to complete or partial airway obstruction, chemical pneumonitis, and surfactant dysfunction. This results in severe respiratory distress. It commonly occurs in significant fetal distress and post-term babies – it rarely occurs before 34 weeks of gestation. Under distress, the fetus gasps and aspirates amniotic fluid.
- Risk factors – mostly causes of fetal hypoxia and distress
- Post-date births (> 42 weeks of gestation)
- Maternal diabetes
- Maternal hypertension
- Pre-eclampsia
- Oligohydramniois
- Placental insufficiency
- Chorioamnionitis
- Smoking
- Substance abuse
- Pathophysiology
- Fetal distress (hypoxia, acidosis, or infection) triggers vagal stimulation, leading to premature relaxation of the anal sphincter and expulsion of meconium into amniotic fluid
- Gasping respiratory movements caused by hypoxia cause aspiration of meconium-stained liquor into the lungs
- Meconium can cause complete or partial obstruction of the airway
- Complete obstruction = absorption atelectasis (patchy)
- Incomplete obstruction = air-trapping and hyperinflation/pneumothorax via ball-valve effect
- Meconium contains pro-inflammatory substances (bile acids, pancreatic enzymes, cytokines) that directly damage alveolar and bronchial epithelium, triggering severe lung inflammation
- This inflammation leads to:
- Alveolar edema and interstitial swelling → Impaired gas exchange
- Surfactant inactivation → Alveolar collapse (atelectasis)
- Neutrophilic infiltration → Further lung damage
- Meconium inhibits nitric oxide (NO) production, leading to pulmonary vasoconstriction and persistent pulmonary hypertension of the newborn (PPHN).
- This worsens hypoxia, creating a vicious cycle of hypoxic pulmonary vasoconstriction → increased right-to-left shunting via the ductus arteriosus and foramen ovale → systemic hypoxemia and cyanosis
- Signs and symptoms
- Coarse breath sounds
- Wheeze on auscultation
- Barrel chest appearance due to air trapping and hyperinflation – ball-valve effect of aspirated meconium
- Meconium stained liquour
- Meconium-stained nails, skin, and umbilical cord
- Green urine after birth – pigments are absorbed in the lungs and excreted in urine
- Hypotonia and diminished reflexes – characteristic of birth asphyxia
- Investigations
- Chest X-ray
- Irregular infiltrates
- Hyperinflation
- Lobar consolidation in severe cases
- Pulmonary air leaks
- Patchy collapse = complete obstruction
- Air trapping = incomplete obstruction
- Arterial blood gases
- Complete Blood Count: rule out infection as the cause of in-utero stress
- Chest X-ray
- Treatment
- Neonatal resuscitation based on status at delivery
- Suction the nose and mouth
- Suction the trachea if:
- Bradycardic
- Poor respiratory effort
- Poor muscle tone
- Positive pressure ventilation and careful SpO2 monitoring
- NICU care
- Insert an umbilical artery catheter to monitor ABGs
- Monitor Hb
- Maintain > 13g/dL
- Surfactant therapy
- Inhaled Nitric Oxide – a pulmonary vasodilator – to treat the persistent pulmonary hypertension of the newborn (PPHN) that results
- Complications
- Chemical pneumonitis
- Persistent pulmonary hypertension of the newborn
- Pulmonary air leaks and Pneumothorax