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Meconium Aspiration Syndrome

  • Author: Melinda B Clark, MD; Chief Editor: Ted Rosenkrantz, MD  more...
 
Updated: Jan 14, 2014
 

Background

The first intestinal discharge from newborns is meconium, which is a viscous, dark-green substance composed of intestinal epithelial cells, lanugo, mucus, and intestinal secretions (eg, bile). Intestinal secretions, mucosal cells, and solid elements of swallowed amniotic fluid are the 3 major solid constituents of meconium. Water is the major liquid constituent, comprising 85-95% of meconium. Meconium is sterile and does not contain bacteria, the primary factor that differentiates it from stool. Intrauterine distress can cause passage into the amniotic fluid. Factors that promote the passage in utero include placental insufficiency, maternal hypertension, preeclampsia, oligohydramnios, and maternal drug abuse, especially of tobacco and cocaine.

Meconium-stained amniotic fluid may be aspirated before or during labor and delivery. Because meconium is rarely found in the amniotic fluid prior to 34 weeks' gestation, meconium aspiration chiefly affects infants born at term and postterm.

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Pathophysiology

In utero meconium passage results from neural stimulation of a maturing GI tract and usually results from fetal hypoxic stress. As the fetus approaches term, the GI tract matures, and vagal stimulation from head or cord compression may cause peristalsis and relaxation of the rectal sphincter leading to meconium passage.

The effects of meconium in amniotic fluid are well documented.[1] Meconium directly alters the amniotic fluid, reducing antibacterial activity and subsequently increasing the risk of perinatal bacterial infection. Additionally, meconium is irritating to fetal skin, thus increasing the incidence of erythema toxicum. However, the most severe complication of meconium passage in utero is aspiration of stained amniotic fluid before, during, and after birth. Aspiration induces hypoxia via four major pulmonary effects: airway obstruction, surfactant dysfunction, chemical pneumonitis, and pulmonary hypertension.

Airway obstruction

Complete obstruction of the airways by meconium results in atelectasis. Partial obstruction causes air trapping and hyperdistention of the alveoli, commonly termed the ball-valve effect. Hyperdistention of the alveoli occurs from airway expansion during inhalation and airway collapse around inspissated meconium in the airway, causing increased resistance during exhalation. The gas that is trapped (hyperinflating the lung) may rupture into the pleura (pneumothorax), mediastinum (pneumomediastinum), or pericardium (pneumopericardium).

Surfactant dysfunction

Meconium deactivates surfactant and may also inhibit surfactant synthesis.[2, 3] Several constituents of meconium, especially the free fatty acids (eg, palmitic, stearic, oleic), have a higher minimal surface tension than surfactant and strip it from the alveolar surface, resulting in diffuse atelectasis.[4]

Chemical pneumonitis

Enzymes, bile salts, and free fatty acids in meconium irritate the airways and parenchyma, causing a release of cytokines (including tumor necrosis factor (TNF-α, interleukin (IL)-1ß, I-L6, IL-8, IL-13), which initiate a diffuse pneumonitis that may begin within a few hours of aspiration.

All of these pulmonary effects can produce a gross ventilation-perfusion (V/Q) mismatch.

Persistent pulmonary hypertension of the newborn

To complicate matters further, many infants with meconium aspiration syndrome (MAS) have primary or secondary persistent pulmonary hypertension of the newborn (PPHN) as a result of chronic in utero stress and thickening of the pulmonary vessels. PPHN further contributes to the hypoxemia caused by meconium aspiration syndrome.[5]

Finally, although meconium is sterile, its presence in the air passages can predispose the infant to pulmonary infection.

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Prognosis

Most infants with meconium aspiration syndrome (MAS) have complete recovery of pulmonary function. Severely affected infants have approximately a 50% risk of developing reactive airway disease in the first 6 months of life.

Prenatal and intrapartum events initiating the meconium passage may cause the infant to have long-term neurologic deficits, including CNS damage, seizures, mental retardation, and cerebral palsy.

Morbidity/mortality

A large retrospective analysis demonstrated the overall mortality rate for meconium aspiration syndrome to be 1.2% in the United States.[7] The mortality rate for meconium aspiration syndrome resulting from severe parenchymal pulmonary disease and pulmonary hypertension is as high as 20%. Other complications include air block syndromes (eg, pneumothorax, pneumomediastinum, pneumopericardium) and pulmonary interstitial emphysema, which occur in 10-30% of infants with meconium aspiration syndrome. The neurologic disabilities of survivors are not due primarily to the aspiration of meconium, but rather by in-utero pathophysiology, including chronic hypoxia and acidosis.[8]

Complications

Children with meconium aspiration syndrome may develop chronic lung disease from intense pulmonary intervention.

Infants with meconium aspiration syndrome have a slightly increased incidence of respiratory infections in the first year of life because the lungs are still in recovery.

Race

A study of 499,096 singleton live births in London, England reported the rates of meconium-stained amniotic fluid varied by ethnicity: blacks (22.6%), south Asian (16.8%), and whites (15.7%). The study also demonstrated that later-gestational-age pregnancies and babies in the breach presentation more often had meconium-stained amniotic fluid.[9]

Sex

Meconium aspiration syndrome equally affects both sexes.

Age

Meconium aspiration syndrome is exclusively a disease of newborns, especially those that are delivered at or beyond the mother's estimated due date.[1]

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Epidemiology

Frequency

United States

In the industrialized world, meconium in the amniotic fluid can be detected in 8-25% of all births after 34 weeks' gestation. Historically, approximately 10% of newborns born through meconium-stained amniotic fluid developed meconium aspiration syndrome. Changes in obstetrical and neonatal practices appear to be decreasing the incidence of meconium aspiration syndrome.[6] Meconium aspiration syndrome was the admission diagnosis for 1.8% of term neonates in one large retrospective study from 1997-2007.[7]

International

In developing countries with less availability of prenatal care and where home births are common, incidence of meconium aspiration syndrome is thought to be higher and is associated with a greater mortality rate.

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Contributor Information and Disclosures
Author

Melinda B Clark, MD Associate Professor of Pediatrics, Department of Pediatrics, Albany Medical College

Melinda B Clark, MD is a member of the following medical societies: Alpha Omega Alpha, Academic Pediatric Association, American Academy of Pediatrics, Medical Society of the State of New York

Disclosure: Nothing to disclose.

Coauthor(s)

David A Clark, MD Chairman, Professor, Department of Pediatrics, Albany Medical College

David A Clark, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Pediatric Society, Christian Medical and Dental Associations, Medical Society of the State of New York, New York Academy of Sciences, Society for Pediatric Research

Disclosure: Nothing to disclose.

Specialty Editor Board

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Brian S Carter, MD, FAAP Professor of Pediatrics, University of Missouri-Kansas City School of Medicine; Attending Physician, Division of Neonatology, Children's Mercy Hospital and Clinics; Faculty, Children's Mercy Bioethics Center

Brian S Carter, MD, FAAP is a member of the following medical societies: Alpha Omega Alpha, American Academy of Hospice and Palliative Medicine, American Academy of Pediatrics, American Pediatric Society, American Society for Bioethics and Humanities, American Society of Law, Medicine & Ethics, Society for Pediatric Research, National Hospice and Palliative Care Organization

Disclosure: Nothing to disclose.

Chief Editor

Ted Rosenkrantz, MD Professor, Departments of Pediatrics and Obstetrics/Gynecology, Division of Neonatal-Perinatal Medicine, University of Connecticut School of Medicine

Ted Rosenkrantz, MD is a member of the following medical societies: American Academy of Pediatrics, American Pediatric Society, Eastern Society for Pediatric Research, American Medical Association, Connecticut State Medical Society, Society for Pediatric Research

Disclosure: Nothing to disclose.

References
  1. Singh BS, Clark RH, Powers RJ, Spitzer AR. Meconium aspiration syndrome remains a significant problem in the NICU: outcomes and treatment patterns in term neonates admitted for intensive care during a ten-year period. J Perinatol. 2009 Jul. 29(7):497-503. [Medline].

  2. Janssen DJ, Carnielli VP, Cogo P, et al. Surfactant phosphatidylcholine metabolism in neonates with meconium aspiration syndrome. J Pediatr. 2006 Nov. 149(5):634-9. [Medline].

  3. Clark DA, Nieman GF, Thompson JE, et al. Surfactant displacement by meconium free fatty acids: an alternative explanation for atelectasis in meconium aspiration syndrome. J Pediatr. 1987 May. 110(5):765-70. [Medline].

  4. Terasaka D, Clark DA, Singh BN, Rokahr J. Free fatty acids of human meconium. Biol Neonate. 1986. 50(1):16-20. [Medline].

  5. Wiswell TE, Tuggle JM, Turner BS. Meconium aspiration syndrome: have we made a difference?. Pediatrics. 1990 May. 85(5):715-21. [Medline].

  6. Yoder BA, Kirsch EA, Barth WH, Gordon MC. Changing obstetric practices associated with decreasing incidence of meconium aspiration syndrome. Obstet Gynecol. 2002 May. 99(5 Pt 1):731-9. [Medline].

  7. Singh BS, Clark RH, Powers RJ, Spitzer AR. Meconium aspiration syndrome remains a significant problem in the NICU: outcomes and treatment patterns in term neonates admitted for intensive care during a ten-year period. J Perinatol. 2009 Jul. 29(7):497-503. [Medline].

  8. Ghidini A, Spong CY. Severe meconium aspiration syndrome is not caused by aspiration of meconium. Am J Obstet Gynecol. 2001 Oct. 185(4):931-8. [Medline].

  9. Balchin I, Whittaker JC, Lamont RF, Steer PJ. Maternal and fetal characteristics associated with meconium-stained amniotic fluid. Obstet Gynecol. 2011 Apr. 117(4):828-35. [Medline].

  10. American College of Obstetricians and Gynecologists. ACOG Committee Opinion No 579: Definition of term pregnancy. Obstet Gynecol. 2013 Nov. 122(5):1139-40. [Medline].

  11. American College of Obstetricians and Gynecologists. ACOG committee opinion no. 561: Nonmedically indicated early-term deliveries. Obstet Gynecol. 2013 Apr. 121(4):911-5. [Medline].

  12. ACOG Committee No. 346: Amnioinfusion Does Not Prevent Meconium Aspiration Syndrome. Obstet & Gynecol. Oct 2006. 108(4):1053-1055.

  13. Velaphi S, Vidyasagar D. Intrapartum and postdelivery management of infants born to mothers with meconium-stained amniotic fluid: evidence-based recommendations. Clin Perinatol. 2006 Mar. 33(1):29-42. [Medline].

  14. Hofmeyr GJ, Xu H. Amnioinfusion for meconium-stained liquor in labour. Cochrane Database Syst Rev. 2010 Jan 20. CD000014. [Medline].

  15. Fraser WD, Hofmeyr J, Lede R, et al. Amnioinfusion for the prevention of the meconium aspiration syndrome. New Eng Journal of Medicine. 2005. 353:909-917.

  16. ACOG Committee Opinion No. 379: Management of delivery of a newborn with meconium-stained amniotic fluid. Obstet Gynecol. 2007 Sep. 110(3):739. [Medline].

  17. Vain NE, Szyld EG, Prudent LM, Wiswell TE, Aguilar AM, Vivas NI. Oropharyngeal and nasopharyngeal suctioning of meconium-stained neonates before delivery of their shoulders: multicentre, randomised controlled trial. Lancet. 2004 Aug 14-20. 364(9434):597-602. [Medline].

  18. [Guideline] Neonatal resuscitation: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Kattwinkel J, Perlman JM, Aziz K, Colby C, Fairchild K, GallagherJ, Hazinski MF, Halamek LP, Kumar P, Little G, McGowan JE, Nightengale B, Ramirez MM, Ringer S, Simon WM, Weiner GM, Wyckoff M, ZaichkinJ. Circulation. 2010. 122:S909 –S919.

  19. Wiswell TE, Knight GR, Finer NN, Donn SM, Desai H, Walsh WF. A multicenter, randomized, controlled trial comparing Surfaxin (Lucinactant) lavage with standard care for treatment of meconium aspiration syndrome. Pediatrics. 2002 Jun. 109(6):1081-7. [Medline].

  20. Dargaville PA, Mills JF. Surfactant therapy for meconium aspiration syndrome: current status. Drugs. 2005. 65(18):2569-91. [Medline].

  21. Dargaville PA. Innovation in surfactant therapy I: surfactant lavage and surfactant administration by fluid bolus using minimally invasive techniques. Neonatology. 2012. 101(4):326-36. [Medline].

  22. El Shahed AI, Dargaville P, Ohlsson A, Soll RF. Surfactant for meconium aspiration syndrome in full term/near term infants. Cochrane Database of Systematic Reviews. 2007. 2:[Full Text].

  23. Collins MP, Lorenz JM, Jetton JR, Paneth N. Hypocapnia and other ventilation-related risk factors for cerebral palsy in low birth weight infants. Pediatr Res. 2001 Dec. 50(6):712-9. [Medline].

  24. Abman SH, Kinsella JP. Inhaled nitric oxide therapy for pulmonary disease in pediatrics. Curr Opin Pediatr. 1998 Jun. 10(3):236-42. [Medline].

  25. Ward M, Sinn J. Steroid therapy for meconium aspiration syndrome in newborn infants. Cochrane Database Syst Rev. 2003. CD003485. [Medline].

  26. Sarkar S, Hussain N, Herson V. Fibrin glue for persistent pneumothorax in neonates. J Perinatol. 2003 Jan. 23(1):82-4. [Medline].

  27. [Guideline] 2005 American Heart Association (AHA) guidelines for cardiopulmonary resuscitation (CPR) and emergency cardiovascular care (ECC) of pediatric and neonatal patients: neonatal resuscitation guidelines. Pediatrics. 2006 May. 117(5):e1029-38. [Medline].

  28. Cialone PR, Sherer DM, Ryan RM, et al. Amnioinfusion during labor complicated by particulate meconium-stained amniotic fluid decreases neonatal morbidity. Am J Obstet Gynecol. 1994 Mar. 170(3):842-9. [Medline].

  29. Dargaville PA, Copnell B. The epidemiology of meconium aspiration syndrome: incidence, risk factors, therapies, and outcome. Pediatrics. 2006 May. 117(5):1712-21. [Medline].

  30. Dargaville PA, South M, McDougall PN. Surfactant and surfactant inhibitors in meconium aspiration syndrome. J Pediatr. 2001 Jan. 138(1):113-5. [Medline].

  31. Glantz JC, Woods JR. Significance of amniotic fluid meconium. Maternal-Fetal Medicine. 1999. 393-403.

  32. Kattwinkel J, Niermeyer S, Denson SE. Textbook of Neonatal Resuscitation. 2000.

  33. Kinsella JP. Meconium aspiration syndrome: is surfactant lavage the answer?. Am J Respir Crit Care Med. 2003 Aug 15. 168(4):413-4. [Medline].

  34. Korones SB, Bada-Ellzey HS. Meconium aspiration. Neonatal Decision Making. 1993. 128-9.

  35. Kugelman A, Gangitano E, Taschuk R, et al. Extracorporeal membrane oxygenation in infants with meconium aspiration syndrome: a decade of experience with venovenous ECMO. J Pediatr Surg. 2005 Jul. 40(7):1082-9. [Medline].

  36. Lo KW, Rogers M. A controlled trial of amnioinfusion: the prevention of meconium aspiration in labour. Aust N Z J Obstet Gynaecol. 1993 Feb. 33(1):51-4. [Medline].

  37. Ranzini AC, Chan L. Meconium and fetal-neonatal compromise. In: Intensive Care of the Fetus and Neonate. 1996: 297-303.

  38. Roberton NRC. Aspiration syndromes. Neonatal Respiratory Disorders. 1996. 313-33.

  39. Soll RF, Dargaville P. Surfactant for meconium aspiration syndrome in full term infants. Cochrane Database Syst Rev. 2000. [Medline].

  40. Usta IM, Mercer BM, Aswad NK, Sibai BM. The impact of a policy of amnioinfusion for meconium-stained amniotic fluid. Obstet Gynecol. 1995 Feb. 85(2):237-41. [Medline].

  41. Whitsett JA, Pryhuber GS, Rice WR, Warner BB, Wert SE. Acute respiratory disorders. Neonatology: Pathophysiology and Management of the Newborn. 1999. 494-508.

  42. Wiswell TE, Gannon CM, Jacob J, et al. Delivery room management of the apparently vigorous meconium-stained neonate: results of the multicenter, international collaborative trial. Pediatrics. 2000 Jan. 105(1 Pt 1):1-7. [Medline]. [Full Text].

  43. Yeh TF. Core Concepts: Meconium Aspiration Syndrome. NeoReviews. 2010. 11:e503-511.

  44. Young TE, Mangum OB. Neofax: A Manual of Drugs Used in Neonatal Care. 1998.

 
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Air trapping and hyperexpansion from airway obstruction.
Acute atelectasis.
Pneumomediastinum from gas trapping and air leak.
Left pneumothorax with depressed diaphragm and minimal mediastinal shift because of noncompliant lungs.
Diffuse chemical pneumonitis from constituents of meconium.
 
 
 
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