Meconium aspiration syndrome (MAS) is a significant neonatal respiratory condition that occurs when a newborn inhales a mixture of meconium and amniotic fluid into the lungs. Common in full-term and post-term infants, MAS can lead to serious complications, including airway obstruction, inflammation, and impaired oxygen exchange.
For respiratory therapists and neonatal care providers, understanding MAS is essential, as prompt recognition and effective respiratory intervention can greatly improve outcomes for affected newborns.
What is Meconium Aspiration Syndrome?
Meconium aspiration syndrome (MAS) is a serious condition that occurs when a newborn inhales a mixture of meconium (the baby’s first stool) and amniotic fluid into the lungs around the time of delivery. This can block the airways, cause inflammation, and interfere with normal breathing and gas exchange.
MAS is more likely in full-term or post-term infants, particularly during a stressful or prolonged labor. Symptoms include rapid breathing, grunting, bluish skin, and poor muscle tone. Prompt medical care, often involving suctioning, oxygen, and sometimes mechanical ventilation, is essential to prevent complications like infection or persistent pulmonary hypertension.
Pathophysiology
Meconium aspiration syndrome (MAS) arises from the aspiration of meconium-stained amniotic fluid into the neonate’s lungs, triggering both mechanical and chemical disturbances.
Mechanically, meconium particles can obstruct airways, leading to air trapping and possible lung overexpansion. This obstruction disrupts optimal ventilation and perfusion in the lungs.
Chemically, meconium irritates lung tissue, inducing an inflammatory response known as chemical pneumonitis. Concurrently, meconium impairs surfactant function, vital for preventing lung collapse.
The culmination of these effects—airway obstruction, inflammation, and surfactant dysfunction—manifests as respiratory distress and impaired oxygenation in the affected newborn.
Causes
Meconium aspiration syndrome is primarily caused by the aspiration of meconium-stained amniotic fluid by a fetus or newborn.
The factors leading to the passage of meconium and its subsequent aspiration include:
- Fetal Stress: Particularly during labor, which can result from oxygen deprivation. This stress might trigger the fetus to pass meconium.
- Prolonged Labor: Longer labors, especially those involving late-term or post-term pregnancies (beyond 40 weeks), can increase the chances of meconium passage.
- Maternal Hypertension: High blood pressure in the mother can stress the fetus, leading to meconium passage.
- Maternal Drug Use: The use of certain drugs during pregnancy, especially tobacco and illicit substances, can increase the risk of MAS.
- Complications with the Umbilical Cord: These might include a knotted cord or a cord wrapped around the baby’s neck, leading to decreased oxygen and increased chances of MAS.
- Infections: Maternal or fetal infections can stress the fetus, prompting meconium passage.
- Diabetes in the Mother: Maternal diabetes can be a risk factor for MAS.
Note: While the presence of meconium in the amniotic fluid doesn’t always lead to MAS, the risk increases when the thick, sticky substance is aspirated, obstructing airways and causing inflammation in the newborn’s lungs.
Symptoms
Symptoms of meconium aspiration syndrome typically manifest shortly after birth. Some common examples includes:
- Respiratory Distress: Difficult, rapid or labored breathing with retractions (when the skin between the ribs pulls in during breathing).
- Cyanosis: A bluish skin color, especially around the mouth and fingertips, indicating a lack of sufficient oxygen.
- Barrel Chest: An abnormally enlarged chest, as the baby tries to take in more air.
- Grunting Sounds: These can be heard when the infant exhales, signaling breathing difficulties.
- Low Apgar Scores: Lower scores on the standard newborn health evaluation, especially in the 1-minute test after birth.
- Decreased Air Entry on One Side: As detected by a stethoscope, this suggests potential lung collapse or pneumothorax (air leakage outside the lungs within the chest).
- Meconium-Stained Amniotic Fluid: The presence of dark, greenish-brown staining or streaking in the amniotic fluid or on the baby’s skin, nails, or umbilical cord.
- Limpness or Lethargy: Decreased muscle tone or activity in the infant.
- Rales or Crackles: Abnormal sounds that can be heard in the lungs when using a stethoscope.
Note: Recognizing these symptoms early is crucial for prompt intervention and treatment, reducing the risk of complications or long-term damage.
Treatment
The treatment for meconium aspiration syndrome is multifaceted and aims to support the infant’s respiratory function while minimizing complications.
Here are the main components of treatment:
- Immediate Suctioning: If meconium-stained amniotic fluid is observed during delivery, the newborn’s mouth and nose may be suctioned immediately upon head emergence to remove meconium before the first breath. Further deep suctioning under the vocal cords might be done after birth if the baby is not vigorous.
- Oxygen Therapy: To support oxygenation, supplemental oxygen is provided, either through a mask, nasal prongs, or an incubator (neonatal intensive care unit).
- Mechanical Ventilation: In severe cases where the baby cannot breathe adequately on their own, a mechanical ventilator may be used. This device pushes air into the baby’s lungs and ensures oxygen delivery.
- Surfactant Replacement Therapy: Surfactant, a substance that helps keep the lungs expanded, can be administered directly into the baby’s lungs. This helps improve lung function and oxygenation.
- Extracorporeal Membrane Oxygenation (ECMO): In extreme cases where other treatments don’t work, ECMO, a technique that oxygenates the baby’s blood outside the body, can be used.
- Antibiotics: As a preventive measure against potential infection, especially since it’s often hard to distinguish between MAS and neonatal infection initially.
- Chest Physiotherapy: This helps in loosening and removing the meconium from the lungs, facilitating easier breathing.
- Supportive Care: This includes maintaining the baby’s body temperature, ensuring proper nutrition (often via intravenous lines until the baby can feed), and monitoring vital signs.
- Nitric Oxide Inhalation: In some cases, inhaled nitric oxide may be used to relax and dilate the blood vessels in the lungs, improving oxygenation.
Note: The severity of MAS and the infant’s response to initial treatments will dictate the extent and duration of these interventions. Collaboration between obstetricians, pediatricians, and neonatologists is crucial for optimal management and outcomes.
Meconium Aspiration Syndrome Practice Questions
1. What is the abbreviation for meconium aspiration syndrome?
MAS
2. What are the characteristics of meconium aspiration syndrome?
Increased temperature (i.e., sign of infection) and signs of respiratory distress (e.g., nasal flaring, grunting, tachypnea, chest retractions).
3. What are the risk factors for meconium aspiration syndrome?
Thick/moderate fresh MEC liquor, late preterm and term babies, SGA/IUGR babies, post-term babies, post-dates, SGA, placental insufficiency, cord compression, fetal distress, small for gestational age, mother is obese, and breech position birth.
4. Is meconium aspiration syndrome more likely to affect preterm or post-term infants?
It is more likely to occur in post-term infants.
5. What are the risk factors of post-birth meconium aspiration syndrome exposure?
Respiratory distress, cold stress, weight loss, jaundice, and infection.
6. What is the epidemiology of deliveries associated with meconium aspiration syndrome?
13% of all deliveries are associated with MSAF, and 5-12% of neonates delivered with MSAF develop meconium aspiration syndrome.
7. What are the clinical manifestations of meconium aspiration syndrome?
Meconium staining of nails, skin, umbilical cord, and placenta; initial respiratory depression followed by tachypnea, retractions, grunting, flaring, prolonged expiratory phase, rales, rhonchi, barrel chest with increased anteroposterior diameter, and cyanosis; neurologic depression may be present; other signs may include apnea, intercostal retractions, barrel chest, and expiratory grunting.
8. What are the diagnostics for meconium aspiration syndrome?
Chest x-ray, arterial blood gas (ABG), and pre/post ductal pulse oximetry.
9. What can be seen on the chest x-ray in meconium aspiration syndrome?
Coarse, streaky, nodular pulmonary densities, often distributed asymmetrically, hyperinflation with flattening of the diaphragm, possible pneumothorax, pneumomediastinum, pleural effusion, cardiomegaly (secondary to hypoxia), irregular densities throughout the lungs with atelectasis and consolidation.
10. What will the ABG results show in an infant meconium aspiration syndrome?
Acute alveolar hyperventilation with hypoxemia (respiratory alkalosis from hyperventilation).
11. What can be seen on pre and postductal oximetry?
Used to evaluate right to left shunting through a patent ductus arteriosus (PDA), and a difference in saturation of greater than 5% suggests PPHN is present.
12. What are the pathological and structural changes associated with meconium aspiration syndrome?
Partially obstructed airways, air trapping, alveolar hyperinflation; pulmonary air leaks; total obstructed airways and absorption atelectasis; edema of the bronchial mucosa and alveolar epithelium; excessive bronchial secretions; alveolar consolidation; and disrupted pulmonary surfactant production.
13. Can meconium aspiration by itself cause an infection?
No, meconium is sterile.
14. What are some risk factors of meconium aspiration?
Fetal distress and post-maturity.
15. How can you manage meconium aspiration syndrome?
Give oxygen, IV fluids, appropriate feeding, and antibiotics.
16. What heart rate is often present in infants with meconium aspiration syndrome?
Tachycardia
17. What is the secondary assessment for meconium aspiration syndrome?
Chest x-ray and ABG
18. What is the treatment and management for meconium aspiration syndrome?
Suction the nasopharynx and oropharynx thoroughly when amniotic fluid is stained, stabilize and transfer to the ICU, vigorous pulmonary hygiene, oxygen therapy, mechanical ventilation, and drug therapy (e.g., antibiotics and steroids).
19. How often is meconium present in births greater than 34-40 weeks?
8-20%
20. How often is there meconium present in births greater than 40-42 weeks?
30%
21. Is meconium rare in babies less than 34-40 weeks?
Yes
22. When does meconium aspiration occur?
If the baby gasps in utero in pregnancy or labor, or if there is meconium in the baby’s mouth when they take their first gasp at birth, it may go into the upper respiratory tract.
23. Is meconium always a sign of a problem?
No, not always.
24. How much does inhaling meconium contribute to perinatal mortality?
2%.
25. What is the most important action for respiratory therapists when assisting in the delivery of a newborn who has aspirated meconium?
Suctioning the meconium from the infant’s airway.
26. What do babies with meconium aspiration syndrome look like?
Their skin is stained green; they may appear limp with a low Apgar score; breathing may be rapid, labored, or absent; and the baby may be post-mature with peeling skin.
27. What are the four main pulmonary effects that meconium aspiration can cause?
Airway obstruction, surfactant dysfunction, chemical pneumonitis, and persistent pulmonary hypertension.
28. What is the effect of airway obstruction?
The airway collapses around the inhaled meconium, which causes increased resistance on exhalation and hyperinflation of lungs due to trapped gas, resulting in a pneumothorax.
29. How does meconium cause chemical pneumonitis?
Enzymes, fats, and bile salts in meconium cause irritation in the airways and alveoli. This chemical response may cause pneumonitis within a few hours of aspiration.
30. Why does meconium cause persistent pulmonary hypertension?
The effects of meconium cause a significant ventilation/perfusion mismatch.
31. What is the treatment for meconium aspiration?
Oxygen therapy to maintain the SpO2 greater than 95%, CPAP, antibiotics, and CXR if tachypnea or RD.
32. What are the complications of meconium aspiration?
Infection, pneumothorax, respiratory failure, and persistent pulmonary hypertension.
33. What can occur from the aspiration of meconium?
Ball valve effect, atelectasis, total airway obstruction, alveolar hyperinflation, and chemical pneumonitis.
34. What is associated with meconium aspiration syndrome when a ball valve effect is present?
Increased FRC
35. What percentage of infants with meconium aspiration syndrome requiring mechanical ventilation will likely develop a pneumothorax?
10-15%
36. When a fetus experiences hypoxemia, it is at risk for which pulmonary complication?
Meconium aspiration
37. What group is at the greatest risk for having meconium aspiration syndrome?
Post-term infants
38. What can occur in infants with confirmed aspirated meconium?
Persistent pulmonary hypertension of the neonate (PPNH), chemical pneumonitis, and airway obstruction.
39. What pulmonary complication is an infant with meconium aspiration syndrome at risk for?
Pneumothorax
40. What should be done for an infant with moderate meconium aspiration that has been stabilized?
Give supplemental oxygen and begin the bronchial hygiene therapy protocol.
41. What medications are needed for an infant with MAS?
Antibiotics, exogenous pulmonary surfactant, and steroids.
42. What clinical manifestation is associated with more negative intrapleural pressures in infants with MAS during inspiration?
Intercostal retractions and nasal flaring.
43. What is the sticky blackish-green material on the newborn baby’s skin?
Meconium
44. What will the chest x-ray show on an infant with meconium aspiration syndrome?
It will likely show consolidation, irregular densities, and possibly atelectasis.
45. How can you clear the airway of an infant with meconium aspiration syndrome?
You may need to intubate with a meconium aspirator and suction the trachea until the airway becomes clear.
46. Do babies recover from meconium aspiration syndrome?
Yes, most babies recover fully from meconium aspiration syndrome with appropriate medical treatment.
47. Are there long-term effects of meconium aspiration syndrome?
While many infants recover without any lasting issues, some may experience long-term respiratory problems or developmental issues due to periods of decreased oxygen.
48. What is the most common symptom seen in infants with meconium aspiration syndrome?
The most common symptom is respiratory distress, characterized by rapid and labored breathing shortly after birth.
49. How to avoid meconium aspiration syndrome?
Close monitoring during labor, avoiding stress to the fetus, and immediate suctioning of the newborn’s airways if meconium is present can help in prevention.
50. Is meconium aspiration syndrome fatal?
While MAS can be severe and does increase the risk of mortality in newborns, it is not often fatal with timely and appropriate medical intervention.
51. What is meconium composed of?
Amniotic fluid, mucus, bile, lanugo, intestinal epithelial cells, and water
52. Why does meconium passage occur in utero?
Often due to fetal hypoxia or distress stimulating intestinal peristalsis and relaxation of the anal sphincter
53. What triggers the first breath that may cause aspiration of meconium?
Gasping respirations due to asphyxia or stress before or during delivery
54. What is the consistency of thick meconium, and why is it concerning?
Sticky and tar-like, which can easily obstruct small airways
55. Why is MAS more common in post-term infants?
Due to longer gestation, they are more likely to experience in utero stress and pass meconium
56. What fetal heart rate pattern may suggest meconium-stained amniotic fluid?
Late or variable decelerations indicating fetal distress
57. What is the Apgar score typically like in a baby with MAS?
Often low at 1 and 5 minutes due to poor respiratory effort and tone
58. What is the hallmark sign of MAS on physical examination?
Green-stained skin or umbilical cord with respiratory distress shortly after birth
59. What is the gold standard diagnostic tool for confirming MAS?
Chest radiography (CXR)
60. Why is surfactant therapy used in MAS?
Meconium inactivates surfactant, and replacing it can improve lung compliance and oxygenation
61. How does MAS contribute to persistent pulmonary hypertension of the newborn (PPHN)?
It causes hypoxia and pulmonary vasoconstriction, leading to right-to-left shunting
62. What is the primary cause of hypoxemia in MAS?
Ventilation-perfusion mismatch due to airway obstruction and inflammation
63. What lung sound is often heard on auscultation in MAS?
Coarse crackles or rhonchi
64. What oxygen saturation goal is typically targeted in infants with MAS?
Greater than 90–95% to ensure adequate tissue oxygenation
65. Why are steroids considered in MAS treatment?
To reduce inflammation associated with chemical pneumonitis
66. How does MAS affect lung compliance?
It decreases compliance due to inflammation, consolidation, and surfactant inactivation
67. What is the role of ECMO in severe MAS cases?
To provide oxygenation and ventilation when conventional support fails
68. When should a meconium aspirator be used during resuscitation?
If the newborn is non-vigorous and meconium is present in the airway
69. Can MAS be prevented through elective C-section?
In some high-risk cases, C-section may reduce the risk of aspiration in compromised infants
70. What type of acid-base imbalance is often seen initially in MAS?
Respiratory acidosis due to hypoventilation and CO₂ retention
71. What is the first step in managing a vigorous newborn with meconium-stained amniotic fluid?
Routine newborn care without airway suctioning
72. What is the first step in managing a non-vigorous newborn with meconium-stained amniotic fluid?
Intubate and suction the trachea using a meconium aspirator
73. What is the function of post-ductal pulse oximetry in MAS evaluation?
To detect differential oxygen saturation and screen for right-to-left shunting
74. What signs indicate a severe case of MAS?
Persistent hypoxia, need for mechanical ventilation, pneumothorax, and signs of PPHN
75. What other neonatal condition must be ruled out when diagnosing MAS?
Neonatal sepsis, as it can mimic similar signs like respiratory distress and low Apgar scores
76. Why does meconium interfere with surfactant function in the lungs?
It disrupts surfactant production and reduces its surface tension-lowering ability, leading to alveolar collapse.
77. What is a key difference between MAS and transient tachypnea of the newborn (TTN)?
MAS is associated with meconium-stained fluid and inflammatory lung changes, while TTN is usually due to retained fetal lung fluid without inflammation.
78. What is the role of high-frequency oscillatory ventilation (HFOV) in MAS?
It may be used in severe cases to reduce barotrauma while improving oxygenation and CO₂ removal.
79. What is the purpose of using nitric oxide therapy in MAS?
To treat persistent pulmonary hypertension of the newborn (PPHN) by promoting pulmonary vasodilation.
80. What maternal conditions increase the risk of MAS?
Preeclampsia, gestational diabetes, post-term pregnancy, and maternal hypertension.
81. What kind of acid-base disturbance is often present in severe MAS?
Mixed respiratory and metabolic acidosis due to hypoxia and poor perfusion.
82. What is the significance of a barrel chest in infants with MAS?
It suggests hyperinflation of the lungs due to air trapping from partial airway obstruction.
83. What are potential neurologic effects of severe MAS?
Seizures, altered consciousness, or hypotonia due to hypoxic-ischemic encephalopathy.
84. What auscultation findings differentiate MAS from neonatal pneumonia?
MAS typically presents with coarse crackles and rhonchi, while pneumonia may include finer crackles and signs of infection.
85. When should surfactant therapy be administered in MAS?
When there is significant respiratory distress and evidence of surfactant inactivation on imaging or labs.
86. What role do antibiotics play in MAS management?
They are used prophylactically or therapeutically if infection is suspected or cannot be ruled out.
87. Why is MAS considered a medical emergency?
Because it can rapidly lead to hypoxemia, respiratory failure, and cardiac instability if untreated.
88. What is the long-term respiratory risk for infants who suffered from MAS?
They may have an increased risk of wheezing disorders or chronic lung disease.
89. Can meconium be aspirated during cesarean delivery?
Yes, if the fetus inhales meconium-stained amniotic fluid before or during delivery.
90. Why is MAS more common in small for gestational age (SGA) infants?
They are more likely to suffer from intrauterine hypoxia, which increases the risk of meconium passage and aspiration.
91. What causes air leaks in infants with MAS?
Overdistension from trapped air due to ball-valve airway obstruction can lead to pneumothorax or pneumomediastinum.
92. What is the role of thermoregulation in MAS management?
Maintaining normothermia helps reduce metabolic stress and oxygen consumption in affected infants.
93. How is MAS severity classified?
Based on the level of respiratory support required, blood gas abnormalities, and the presence of complications like PPHN or pneumothorax.
94. How soon after birth do MAS symptoms usually appear?
Symptoms typically begin within the first hours after delivery.
95. Why is continuous monitoring necessary for infants with MAS?
To detect and treat sudden respiratory or cardiovascular deterioration promptly.
96. What does the presence of coarse bilateral infiltrates on chest X-ray suggest in MAS?
Widespread meconium distribution with airway inflammation and possible atelectasis.
97. How can clinicians distinguish MAS from congenital diaphragmatic hernia (CDH)?
CDH may present with bowel sounds in the chest and scaphoid abdomen, whereas MAS has meconium-stained fluid and typical respiratory signs.
98. What is the role of sedation in mechanically ventilated MAS patients?
It helps reduce oxygen consumption and prevent ventilator asynchrony.
99. What is the potential cardiovascular effect of MAS-induced hypoxemia?
It may cause pulmonary vasoconstriction leading to right heart strain or failure.
100. What is the significance of oxygenation index (OI) in MAS?
A high OI may indicate the need for advanced therapies like inhaled nitric oxide or ECMO.
Related: Meconium Aspiration Syndrome: Case Study (Clinical Scenario)
Final Thoughts
Meconium aspiration syndrome (MAS) remains an important concern in neonatal respiratory care. For respiratory therapists, understanding MAS is essential for early identification and timely intervention. Their skills in airway management, oxygen therapy, and mechanical ventilation are vital in improving outcomes and preventing complications.
With proper care, most infants with MAS go on to lead healthy lives, underscoring the importance of prompt and skilled respiratory support from birth.
Written by:
John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.
References
- Faarc, Walsh Brian PhD Rrt-Nps Rrt-Accs Rpft. Neonatal and Pediatric Respiratory Care. 5th ed., Saunders, 2018.
- Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
- “Meconium Aspiration Syndrome: An Insight.” National Center for Biotechnology Information, U.S. National Library of Medicine, Apr. 2010.