Meconium aspiration syndrome (MAS) occurs when the infant breathes in meconium either before, during or after labor. Meconium is the first fecal material produced by the infant, and when it is passed before birth it can mix with the amniotic fluid in the womb. With aspiration, fluid accumulates in the lungs which impairs oxygenation and results in neonatal hypoxia.

You can listen to the following information in episode 212 of the Straight A Nursing podcast, available from this website or wherever you get your podcasts.

Meconium aspiration syndrome pathophysiology

meconium aspiration syndrome (MAS)As the infant inhales or gasps when in distress, the meconium/amniotic fluid mixture enters the airway causing airway obstruction, disruption of surfactant, pulmonary hypertension, and aspiration pneumonitis (also known as chemical pneumonitis).

Airway obstruction – the sticky substance can completely occlude the airways leading to atelectasis, while partial obstruction leads to the infant not being able to fully exhale which distends the alveoli and leads to air trapping. This hyperinflation of the lungs can lead to air entering the pericardium, mediastinum and pleura (pneumothorax).

Surfactant disruption – Recall that surfactant is a detergent-like mixture of fats and proteins that decreases alveolar surface tension and prevents alveoli from collapsing. Without adequate surfactant, alveoli collapse every time the infant exhales, which decreases the amount of surface area available for gas exchange. The overall result is atelectasis and significant hypoxemia. 

Persistent pulmonary hypertension of the newborn (PPHN) – As a result of respiratory distress, the pulmonary vasculature constricts. This increases pulmonary resistance, which decreases lung tissue perfusion and pulmonary blood flow. The increased pulmonary pressure can even cause the infant’s circulation to revert partially to fetal circulation where blood shunts from the right to the left through the ductus arteriosus and foramen ovale. As this process continues, the infant goes into an acidotic state.

Aspiration or chemical pneumonitis – The bile salts, intestinal epithelial cells and other material of the meconium irritate and cause inflammation of the delicate pulmonary tissues. At its most severe, this can lead to acute respiratory distress syndrome (ARDS)

Who is most at risk for MAS?

Babies most at risk for MAS are those born post-term due to long and complicated deliveries. Additionally, post-term infants are more likely to have a bowel movement in utero due to more cholinergic innervation and higher levels of a hormone that regulates gastric motility. Other factors that contribute to the presence of meconium in the womb are long labor or delivery, prolonged rupture of membranes, preeclampsia, oligohydramnios, placental insufficiency, fetal hypoxia, fetal stress, umbilical cord compression, intrauterine growth restriction, maternal infection, chorioamnionitis, maternal diabetes, maternal nicotine use, and maternal drug abuse. Additionally, the use of some intrapartum medications can predispose the passage of meconium including oxytocin and misoprostol.

When meconium is present in the amniotic fluid, its consistency is vitally important in the severity of the condition. Studies show that when the meconium is thicker, infants have a 5-7X increase in risk of perinatal death.

How common is MAS?

The presence of meconium in the amniotic fluid occurs in about 8-25% of all births after the 34th week of gestation. Of those, only about 10% develop MAS with the incidence decreasing in correlation with advances in obstetrics and neonatal care. Racial disparities do exist when it comes to MAS with an 80% higher risk of meconium-stained amniotic fluid amongst non-Hispanic blacks vs non-Hispanic whites.

What are the long-term implications of MAS?

Though most neonates have full recovery from MAS, they are likely to be more prone to respiratory infection in the first year of life. Those with more severe disease are at higher risk for developing reactive airway disease as well as other complications such as bronchopulmonary dysplasia, pulmonary hypertension and even pneumothorax.

Significantly low oxygen levels can cause long-lasting neurological deficits such as cerebral palsy, developmental delay and seizures. 

Now that you’ve got a solid background in MAS, let’s learn how to manage these patients so you can feel confident on your nursing school exams. To do that, we’ll be using the Straight A Nursing LATTE method.

L: How does the patient LOOK?

When the aspiration occurs, the infant will display signs of respiratory distress including gasping, nasal flaring, accessory muscle use, bradycardia, cyanosis, limpness and yellow or green-stained skin. Their APGAR score will be low based on these findings.

Other signs/symptoms of meconium aspiration syndrome include:

  • A flat fetal strip or one with many late decels, indicating significant fetal distress
  • The mother may notice decreased fetal movement
  • Low oxygen saturation levels
  • Elevated carbon dioxide levels (hypercapnia); acidotic cord blood gases
  • Hypotension
  • Crackles upon auscultation
  • Barrel chest, air trapping, hyperinflation on x-ray
  • Streaky or patchy areas on x-ray sometimes described as “salt and pepper,” indicating pneumonitis
  • Presence of meconium below the vocal cords
  • Respiratory alkalosis due to tachypnea and hyperventilation which then transitions to respiratory acidosis as the infant tires.
  • Respiratory acidosis is also related to air trapping which causes accumulation of carbon dioxide.

A: How do you ASSESS the patient?

One of the key assessments you will conduct on any newborn is the APGAR score, paying careful attention to cardiovascular status, respiratory status and skin color. 

  • Cardiovascular status – The infant may be tachycardic in an attempt to compensate, but will most likely exhibit bradycardia due to hypoxia. 
  • Respiratory status – Auscultation will likely reveal crackles or rales due to the accumulation of fluid in the lungs. The child will most likely be in obvious respiratory distress.
  • Skin color – The meconium-stained amniotic fluid can color the umbilical cord and possibly also the skin a yellow or greenish color. Higher levels of meconium in the amniotic fluid tend to create more significant stains. Cyanosis may also be present. For more information about assessing skin signs in infants, including infants with darker skin tones, check out this article.

T: What TESTS will be ordered?

Common tests for infants with suspected or confirmed MAS include chest x-ray and or chest CT, cord blood gases and ABG analysis. The physician may order an ultrasound of the lungs for early diagnosis while a laryngoscopy can identify meconium in and below the vocal cords. 

T: What TREATMENTS will be provided?

  • For a neonate in respiratory distress, the recommendation is to initiate neonatal resuscitation procedures (NRP) with positive pressure ventilation (PPV) utilized quickly – ideally in the first minute after delivery.
  • If ventilating the neonate does not produce the desired result, tracheal suctioning may be warranted. Note that routine oropharyngeal and nasopharyngeal suctioning used to be the norm in all deliveries, but studies are showing it could potentially cause more harm than benefit. If suctioning occurs, it will most likely be beneath the glottis in infants with very poor APGAR scores. 
  • Surfactant lavage therapy may be utilized for infants with severe respiratory distress. This procedure involves introducing exogenous surfactant into the lungs and studies show it can result in rapid improvements, reduced need for mechanical ventilation, and decreased duration of oxygen therapy. 
  • Inhaled nitric oxide allows the blood vessels to dilate, which decreases pulmonary vascular resistance and improves oxygenation. 
  • Extracorporeal membrane oxygenation (ECMO) may be used for very sick infants in severe respiratory failure or who have significant pulmonary hypertension. In ECMO, cannulas are placed which draw blood from the infant, send it to a machine for gas exchange, and then return it to the child fully oxygenated. 
  • Oxygen therapy will depend on the severity of the respiratory dysfunction and can range from hood oxygen or nasal cannula to CPAP and mechanical ventilation. For significantly ill neonates, high-frequency oscillatory ventilation (HFOV) may be necessary. You can learn more about ventilator basics here.
  • Chest physiotherapy and postural drainage have shown to have a significant favorable impact in improving lung function in infants with MAS.
  • Antibiotics may be necessary if the infant develops infections, but are not routinely used for managing MAS specifically. However, the infant could be prescribed broad-spectrum antibiotics while blood culture results are pending as MAS can mimic other conditions such as sepsis or bacterial pneumonia.
  • Therapeutic hypothermia is utilized for infants who develop hypoxic ischemic encephalopathy (HIE). In infants that meet specific criteria, cooling measures are aimed at lowering the body temperature to 91-degrees Fahrenheit for a period of 72 hours in order to allow the brain time to heal.

E: How do you EDUCATE the family?

Having a child in the NICU is a stressful time for parents and family members. Teaching should focus on specific interventions being done for the child with a goal of including the family in as much of the infant’s care as possible. 

You also want to teach the parents that the child could have long-term effects such as chronic lung disease or developmental delays if hypoxia was present. Teaching will be catered to specific concerns as needed.

In addition, teach the parents of the risk factors for MAS, especially if they are planning to have more children. Some factors such as gestational diabetes and maternal hypertension could potentially be controlled with adequate medical care. If the mother has limited access to healthcare, provide information on community resources (or coordinate with the hospital social worker).

Whether meconium is sterile or not is an ongoing debate and the family may ask why the child is not receiving antibiotics. Teach the family that antibiotics are typically only used if the infant develops an infection. However, empiric antibiotics will likely be started if the infant is at high risk for infection (such as prolonged ROM) and then discontinued if blood cultures are negative. 

Prior to discharge, teach caregivers how to recognize signs of respiratory distress such as lethargy, poor eating, cyanosis, nasal flaring, and intercostal or supraclavicular retractions.


I hope this overview of MAS was helpful for you in preparing for exams or a clinical day in the NICU. If you’d like to learn more about pediatrics, come right this way!

Change the way you study with study sesh for nursing students


Autilio, C., Echaide, M., Shankar-Aguilera, S., Bragado, R., Amidani, D., Salomone, F., Pérez-Gil, J., & De Luca, D. (2020). Surfactant Injury in the Early Phase of Severe Meconium Aspiration Syndrome. American Journal of Respiratory Cell and Molecular Biology63(3), 327–337.

Basu, S., Kumar, A., & Bhatia, B. D. (2007). Role of antibiotics in meconium aspiration syndrome. Annals of Tropical Paediatrics27(2), 107–113.

Benioff Children’s Hospitals. (n.d.). Meconium Aspiration Syndrome | Conditions | UCSF Benioff Children’s Hospitals

Birth Injury Help Center. (n.d.). Meconium Aspiration Syndrome

Brandt, J. P., & Mandiga, P. (2022). Histology, Alveolar Cells. In StatPearls. StatPearls Publishing.

Burleigh, D. E. (1988). Evidence for a functional cholinergic deficit in human colonic tissue resected for constipation. The Journal of Pharmacy and Pharmacology40(1), 55–57.

Children’s Minnesota. (n.d.). Surfactant

Cincinnati Children’s. (n.d.). Extracorporeal Membrane Oxygenation (ECMO) in Infants & Children

Dargaville, P. A. (2012). Innovation in surfactant therapy I: Surfactant lavage and surfactant administration by fluid bolus using minimally invasive techniques. Neonatology101(4), 326–336.

FRCPC, J. R. M., Davros, W., Paladin, A., Lee, E., & Carrico, C. (2013). Pediatric Radiology. Oxford University Press.

Geis, G. (n.d.). Meconium Aspiration Syndrome: Background, Pathophysiology, Etiology

Geis, G. (2021). Meconium Aspiration Syndrome: Background, Pathophysiology, Etiology

Goel, A., & Nangia, S. (2017). Meconium aspiration syndrome: Challenges and solutions. Research and Reports in Neonatology7, 19–28.

Goldsmith, J. P. (2008). Continuous positive airway pressure and conventional mechanical ventilation in the treatment of meconium aspiration syndrome. Journal of Perinatology28(3), S49–S55.

Hao, L., & Wang, F. (2019). Effectiveness of high-frequency oscillatory ventilation for the treatment of neonatal meconium aspiration syndrome. Medicine98(43), e17622.

Johns Hopkins Medicine. (n.d.). Meconium Aspiration Syndrome | Johns Hopkins Medicine

Kang, S.-M., Jo, C.-K., Lee, S.-Y., & Kim, M.-J. (2019). Empirical Antibiotics in Non-Ventilated Cases of Meconium Aspiration Syndrome. Neonatal Medicine26(2), 80–84.

Kelly, L. E., Shivananda, S., Murthy, P., Srinivasjois, R., & Shah, P. S. (2017). Antibiotics for neonates born through meconium‐stained amniotic fluid. The Cochrane Database of Systematic Reviews2017(6), CD006183.

Kitazawa, T., & Kaiya, H. (n.d.). Frontiers | Motilin Comparative Study: Structure, Distribution, Receptors, and Gastrointestinal Motility | Endocrinology

Liu, J., Cao, H.-Y., & Fu, W. (n.d.). Lung ultrasonography to diagnose meconium aspiration syndrome of the newborn

Meconium Aspiration Syndrome. (n.d.-a).

Meconium Aspiration Syndrome. (n.d.-b).

MedlinePlus. (n.d.). Meconium aspiration syndrome: MedlinePlus Medical Encyclopedia

Meyers, M., Rodrigues, N., & Ari, A. (2019). High-frequency oscillatory ventilation: A narrative review. Canadian Journal of Respiratory Therapy: CJRT = Revue Canadienne de La Therapie Respiratoire: RCTR55, 40–46.

Nahar, S. (2019). ROLE OF CHEST PHYSIOTHERAPY IN MECONIUM ASPIRATION SYNDROME: A CASE STUDY. International Journal of Scientific Research8.

Nangia, S., Thukral, A., & Chawla, D. (2017). Tracheal suction at birth in non‐vigorous neonates born through meconium‐stained amniotic fluid. The Cochrane Database of Systematic Reviews2017(5), CD012671.

Nationwide Children’s. (n.d.). Chest Physiotherapy—Infants Newborn to 12 Months

NNP-BC, E. P. T., DNP, RN, & NNP-BC, M. E. H., DNP, RN. (2018). Physical Assessment of the Newborn: A Comprehensive Approach to the Art of Physical Examination. Springer Publishing Company.

Nouraeyan, N., Lambrinakos-Raymond, A., Leone, M., & Sant’Anna, G. (2014). Surfactant administration in neonates: A review of delivery methods. Canadian Journal of Respiratory Therapy: CJRT = Revue Canadienne de La Thérapie Respiratoire : RCTR50(3), 91–95.

Olicker, A. L., Raffay, T. M., & Ryan, R. M. (2021). Neonatal Respiratory Distress Secondary to Meconium Aspiration Syndrome. Children8(3), 246.

PK, R., Lakshminrusimha, S., & Vidyasagar, D. (2018). Essentials of Neonatal Ventilation, 1st edition, E-book. Elsevier Health Sciences.

Rathoria, R., Rathoria, E., Bansal, U., Mishra, M., Jalote, I., Shukla, N. K., & Agarwal, D. (2018). Study of risk factors and perinatal outcome in meconium stained deliveries from a district of Uttar Pradesh, India. International Journal of Reproduction, Contraception, Obstetrics and Gynecology7(9), 3605.

Shaikh, M., Waheed, K. A. I., Javaid, S., Gul, R., Hashmi, M. A., & Fatima, S. T. (n.d.). DETRIMENTAL COMPLICATIONS OF MECONIUM ASPIRATION SYNDROME AND THEIR IMPACT ON OUTCOME. J Ayub Med Coll Abbottabad, 4.

The American College of Obstetricians and Gynecologists. (n.d.-a). Delivery of a Newborn With Meconium-Stained Amniotic Fluid | ACOG

The American College of Obstetricians and Gynecologists. (n.d.-b). When Pregnancy Goes Past Your Due Date | ACOG

University of  Michigan Health. (n.d.). Nitric oxide (inhalation gas) | Michigan Medicine