Meconium Aspiration Syndrome 

  • Author: Melinda B Clark, MD; Chief Editor: Ted Rosenkrantz, MD   more...
 
Updated: Mar 30, 2010
 

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 at term and postterm.

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Pathophysiology

In utero meconium passage results from neural stimulation of a mature 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. 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 4 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.[1] 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.

Chemical pneumonitis

Enzymes, bile salts, and fats 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) and resulting in a diffuse pneumonitis that may begin within a few hours of aspiration.

All of these pulmonary effects can produce 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.

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

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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 practice appear to be decreasing the incidence of meconium aspiration syndrome.[2]

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.

Mortality/Morbidity

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.

Race

No racial predilection is known.

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 after their due date.[3]

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Contributor Information and Disclosures
Author

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

Melinda B Clark, MD is a member of the following medical societies: Alpha Omega Alpha, Ambulatory Pediatric Association, American Academy of Pediatrics, and 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 & Dental Society, Medical Society of the State of New York, New York Academy of Sciences, and Society for Pediatric Research

Disclosure: Nothing to disclose.

Specialty Editor Board

Steven M Donn, MD  Professor of Pediatrics, University of Michigan Medical School; Director, Division of Neonatal-Perinatal Medicine, Department of Pediatrics, CS Mott Children's Hospital, University of Michigan Health System

Steven M Donn, MD is a member of the following medical societies: American Pediatric Society

Disclosure: Nothing to disclose.

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 (Neonatology), Vanderbilt University School of Medicine; Director, Neonatal Follow-up Program, Monroe Carell Jr Children's Hospital at Vanderbilt

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 Society for Bioethics and Humanities, American Society of Law, Medicine & Ethics, National Hospice and Palliative Care Organization, Society for Pediatric Research, and Southern Society for Pediatric Research

Disclosure: Nothing to disclose.

Carol L Wagner, MD  Professor of Pediatrics, Medical University of South Carolina

Carol L Wagner, MD is a member of the following medical societies: American Academy of Pediatrics, American Chemical Society, American Medical Women's Association, American Public Health Association, American Society for Bone and Mineral Research, American Society for Clinical Nutrition, Massachusetts Medical Society, National Perinatal Association, and Society for Pediatric Research

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 Medical Association, American Pediatric Society, Connecticut State Medical Society, Eastern Society for Pediatric Research, and Society for Pediatric Research

Disclosure: Nothing to disclose.

References

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

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

  3. 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. Jul 2009;29(7):497-503. [Medline].

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

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

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

  7. [Guideline] American Academy of Pediatrics, American Heart Association. Neonatal Resuscitation Program. 5th ed. 2006.

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

  9. 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 [serial online]. 2007;2:Accessed 6/30/2008. [Medline]. Available at www.cochrane.org/reviews/en/ab002054.html.

  10. 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. Dec 2001;50(6):712-9. [Medline].

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

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

  13. [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. May 2006;117(5):e1029-38. [Medline].

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

  15. 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. Mar 1994;170(3):842-9. [Medline].

  16. 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. May 1987;110(5):765-70. [Medline].

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

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

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

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

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

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

  23. 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. Jul 2005;40(7):1082-9. [Medline].

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

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

  26. Roberton NRC. Aspiration syndromes. In: Neonatal Respiratory Disorders. 1996:313-33.

  27. Soll RF, Dargaville P. Surfactant for meconium aspiration syndrome in full term infants. Cochrane Database Syst Rev. 2000;CD002054. [Medline].

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

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

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

  31. 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. Jan 2000;105(1 Pt 1):1-7. [Medline]. [Full Text].

  32. 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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