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Meconium Aspiration Syndrome

Meconium aspiration syndrome occurs in a small proportion of neonates whose respiratory system is contaminated by the meconium and its content. The exact pathogenesis remains unknown, but conditions that lead to fetal stress and intrauterine hypoxia seem to be the most important risk factors. Tachypnea, grunting, and respiratory insufficiency are the main manifestations of this syndrome. Because of the life-threatening risk, close monitoring for possible respiratory distress in the first few days of life is needed. Together with clinical assessment, the early use of imaging studies (either plain radiography or ultrasonography) is recommended in the workup.


The signs and symptoms of meconium aspiration syndrome stem from the introduction of meconium into the respiratory tree [1] [2] [3] [4]. It is well known that intrauterine hypoxia (which can occur due to numerous disorders and events, examples being placental insufficiency, preeclampsia, maternal abuse of tobacco and drugs, as well as oligohydramnios) is the main facilitator for the induction of meconium passage [1]. Under physiological circumstances, the meconium (composed of gastrointestinal content, bile acids, pancreatic juice, blood, lanugo, and cellular debris) is a sterile mix of substances before the fetus is expelled from the uterus [1] [5]. In approximately 1 in 7 births, the amniotic fluid is stained with meconium, but it is still not understood why only 5-9% of neonates exposed to a meconium-stained amniotic fluid (MSAF) develop meconium aspiration syndrome [1] [3]. As meconium invades the lungs, neonates suffer from decreased lung compliance, eventually leading to hypoxia and tachypnea [1] [2] [3] [5]. Grunting is a particularly important sign that should immediately raise suspicion toward respiratory distress [6]. In fact, supplemental oxygen is almost always necessary to sustain adequate oxygen saturation in patients with MAS [5].

  • Non-selective PDE inhibitors, such as methylxanthines, increase concentrations of cAMP and cGMP in the cells leading to bronchodilation and vasodilation.[en.wikipedia.org]
Fever of Unknown Origin
  • Pregnancy induced hypertension in 3, fetal decelaration in 4, chorioamnionitis in 3, premature rupture of membranes in 3 maternal drug use in 6, sickle-cell disease in 4, fever of unknown origin in 3, and presence of prolapsed cord in 3.[doi.org]
  • In addition, inhalation of GCs may worsen the course of bacterial infections after initial improvement and may increase the risk of oropharyngeal candidiasis, dysphonia, cough, throat irritation and other local side effects [ 3 ].[doi.org]
Barrel Chest
  • Examiners will check the baby for the following signs and symptoms that suggest MAS: Rapid breathing Barrel-chest Low Apgar score (Appearance, Pulse, Grimace, Activity, and Respiration) Cyanosis (blue color of skin) MAS can be confirmed with several tests[study.com]
  • Budesonide is an inhalational GC used in the treatment of bronchial asthma, non-infectious rhinitis (including hay fever and other allergies) and nasal polyposis.[doi.org]
Skin Atrophy
  • Other issues can arise, such as aggravation of diabetes mellitus, osteoporosis, skin atrophy and growth retardation in children.[en.wikipedia.org]
  • Hydrocortisone is a synthetic equivalent of cortisol and used as an immunosuppressive drug in severe allergic reactions such as anaphylaxis and angioedema.[doi.org]
  • The reported high morbidity among the long-time survivors, Macrocephaly developed in 24% of the ECMO group.[doi.org]
  • […] dyslipidemia, reduced fibrinolysis, hypertension, posterior subcapsular cataract, exacerbation of glaucoma, increased intracranial pressure, peptic ulcers, upper gastrointestinal bleeding, immunosuppression, neuropsychiatric disturbances, osteoporosis, myopathy[doi.org]


The diagnosis of meconium aspiration syndrome can be life-threatening without early treatment [2], which is why an immediate postnatal clinical assessment is of critical importance. Evaluation of neonates through Apgar scoring is one of the most important steps when it comes to this condition, followed by determination of oxygen saturation, particularly if signs of hypoxia are present. Meconium aspiration syndrome is much more likely to develop if a thick meconium present, if fetal distress is observed, or if the Apgar score is < 7 in the first 5 minutes after birth [6]. For this reason, many authors advise that all neonates who are exposed to MSAF should be monitored for the first 24 hours in case respiratory distress develops [1]. Additional steps that may be useful are imaging studies and arterial blood gas (ABG) analysis [1]. Plain radiography can show overexpansion of the lungs with patchy infiltrates, whereas consolidation, atelectasis, and coalescing B-lines are typical signs observed on ultrasonography [1] [4]. The convenient real-time imaging provided by the latter technique can be rapidly employed yielding reliable results, with no exposure of the patient to radiation. Ultrasonography is considered superior to X-rays, and should be performed whenever clinical suspicion of meconium aspiration syndrome exists [4].

Decreased Lung Compliance
  • As meconium invades the lungs, neonates suffer from decreased lung compliance, eventually leading to hypoxia and tachypnea. Grunting is a particularly important sign that should immediately raise suspicion toward respiratory distress.[symptoma.com]
  • Although respiratory distress has many causes (e.g., upper airway obstruction, severe metabolic acidemia etc.), most commonly it suggests decreased lung compliance and the presence of parenchymal lung disease.[clinicaladvisor.com]
  • In the first 15 minutes of meconium aspiration, there is obstruction of larger airways which causes increased lung resistance, decreased lung compliance, acute hypoxaemia, hypercapnia, atelectasis and respiratory acidosis.[en.wikipedia.org]
Ischemic Changes
  • The presence of meconium in the amniotic fluid may cause ischemic changes of the lungs, umbilical cord and placenta [ 7 ].[doi.org]


  • Arterial blood gases were measured immediately before treatment, and again at 3 and 6 hours post-treatment. Chest x-rays were taken 6 and 24 hours after treatment.[ncbi.nlm.nih.gov]
  • In general, treatment of MAS is more supportive in nature.[en.wikipedia.org]


  • The presence of meconium was associated with severe asphyxia and carried a bad prognosis with an increased risk of developing hypoxia (58.3 %), need of mechanical ventilatory support (43.1 %), respiratory and/or metabolic acidosis (30.6 %), pulmonary[ncbi.nlm.nih.gov]
  • Deliver before 42 weeks Close monitoring of high risk babies and mom What is the prognosis for MAS? Mild cases: resolve in 2-4 days Severe cases: Permanent airway damage Chronic lung disease If severity of hypoxia: Cerebral palsy[quizlet.com]
  • Most newborns with meconium aspiration syndrome have an excellent prognosis. However, occasionally, if the disorder is severe, especially if it leads to persistent pulmonary hypertension of the newborn, it can be fatal.[msdmanuals.com]
  • Other treatments may include: Antibiotics to treat infection Breathing machine (ventilator) to keep the baby's lungs inflated Oxygen to keep blood levels normal Radiant warmer to maintain body temperature Outlook (Prognosis) In most cases, the outlook[nicklauschildrens.org]
  • Severely affected babies have a much more guarded prognosis; they may develop chronic lung disease, developmental abnormalities and hearing loss. Sometimes very severe cases of MAS can be fatal.[luriechildrens.org]


  • Etiology Risk factors (not always found) placental insufficiency maternal hypertension and preeclampsia oligohydramnion, maternal drug abuse Aspiration of meconium induces hypoxia via airway obstruction surfactant dysfunction chemical pneumonitis pulmonary[atlases.muni.cz]
  • One-third of cases • Depending on the extent of hypoxemia, echocardiography should be performed to ascertain: the degree to which the right-to-left shunting is contributing to the infant's overall hypoxemia and  to exclude congenital heart disease as the etiology[slideshare.net]
  • The most common etiology of neonatal respiratory distress is transient tachypnea of the newborn; this is triggered by excessive lung fluid, and symptoms usually resolve spontaneously.[aafp.org]


  • The epidemiology of meconium aspiration syndrome: incidence, risk factors, therapies, and outcome. Pediatrics. 2006 May. 117 (5):1712-21. [Medline]. Dargaville PA, South M, McDougall PN.[emedicine.com]
  • One study suggests that fetal pancreatic digestive enzymes may play a part in causing the lung damage seen in MAS. [ 2 ] Epidemiology The figure quoted for infants born with meconium-stained liquor in the industrialised world is 8-25% of births after[patient.info]
  • Developmental Epidemiology Network Investigators. Pediatr Res 1999; 46: 566–75. 42. Mittendorf R, Montag AG, MacMillan W, et al .[jpatholtm.org]
  • (Epidemiology of respiratory failure in the newborn.) RCT on the role of inhaled nitric oxide and HFOV in MAS. (Cochrane review on amnioinfusion.) Copyright 2017, 2013 Decision Support in Medicine, LLC. All rights reserved.[clinicaladvisor.com]
Sex distribution
Age distribution


  • The concepts of pathophysiology and management of meconium stained amniotic fluid (MSAF) and meconium aspiration syndrome have undergone tremendous change in recent years.[ncbi.nlm.nih.gov]


  • To provide an overview of the advances in our knowledge concerning the obstetric approaches to the prevention of MAS.[ncbi.nlm.nih.gov]
  • It functions to lower surface tension (to allow for lung expansion during inspiration), stabilise alveoli at the end of expiration (to prevent alveolar collapse) and prevents lung oedema.[en.wikipedia.org]



  1. Swarnam K, Soraisham AS, Sivanandan S. Advances in the Management of Meconium Aspiration Syndrome. Int J Pediatr. 2012;2012:359571.
  2. Dargaville PA. Respiratory Support in Meconium Aspiration Syndrome: A Practical Guide. Int J Pediatr. 2012;2012:965159.
  3. Lee J, Romero R, Lee KA, et al. Meconium aspiration syndrome: a role for fetal systemic inflammation. Am J Obstet Gynecol. 2016;214(3):366.e1-9.
  4. Piastra M, Yousef N, Brat R, Manzoni P, Mokhtari M, De Luca D. Lung ultrasound findings in meconium aspiration syndrome. Early Hum Dev. 2014;90 Suppl 2:S41-43.
  5. Lindenskov PH, Castellheim A, Saugstad OD, Mollnes TE. Meconium aspiration syndrome: possible pathophysiological mechanisms and future potential therapies. Neonatology. 2015;107(3):225-2s30.
  6. Liu WF, Harrington T. Delivery room risk factors for meconium aspiration syndrome. Am J Perinatol. 2002;19(7):367-378.

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Last updated: 2019-06-28 09:51