Meconium Aspiration Syndrome Year 4 Paediatrics Notes

Meconium Aspiration Syndrome Year 4 · Paediatrics Collection: 4TH YEAR ALL NOTES / PAEDS / PAEDS 4.3 / Munge / NEONATOLOGY -- Slide 1 Meconium Aspiration Syndrome Dr Rose Munge Slide 2 Meconium aspiration syndrome (MAS) is the aspiration of stained amniotic fluid, which can occur before, during, or immediately after birth.\nMeconium is the first intestinal discharge from newborns, a viscous, dark-green substance composed of intestinal epithelial cells, lanugo, mucus, and intestinal secretions (eg, bile) Water is the major liquid constituent (85-95%) of meconium; the remaining 5-15% consists of solid constituents, primarily intestinal secretions, mucosal cells, and solid elements of swallowed amniotic fluid, such as proteins and lipids. Meconium is sterile and does not contain bacteria\nIntrauterine distress can cause passage of meconium into the amniotic fluid. Slide 3 Factors that promote the passage in utero include placental insufficiency, maternal hypertension, preeclampsia, oligohydramnios, infection, acidosis, and maternal drug abuse, especially tobacco and cocaine. Because meconium is rarely found in the amniotic fluid prior to 34 weeks' gestation, meconium aspiration primarily affects infants born at term and postterm. Slide 4 In utero meconium passage results from neural stimulation of a maturing gastrointestinal (GI) tract, usually due to foetal hypoxic stress.\nAs the foetus approaches term, the GI tract matures, and vagal stimulation from head or spinal cord compression may cause peristalsis and relaxation of the rectal sphincter, leading to meconium passage. Meconium directly alters the amniotic fluid, reducing antibacterial activity and subsequently increasing the risk of perinatal bacterial infection. Meconium is irritating to foetal skin, thus increasing the incidence of erythema toxicum.\nThe most severe complication of meconium passage in utero is MAS.\nAspiration of meconium-stained amniotic fluid may occur if the foetus is in distress, leading to a gasping breathing pattern.\nThis aspiration induces hypoxia via four major pulmonary effects: airway obstruction, surfactant dysfunction, chemical pneumonitis, and pulmonary hypertension. Slide 5 Airway obstruction Complete obstruction of the airways by meconium results in atelectasis.\nPartial obstruction causes air trapping and hyperdistention of the alveoli, commonly termed the ball-valve effect.\nHyperdistention of the alveoli occurs from airway expansion during inhalation and airway collapse around inspissated meconium in the airway, causing increased resistance during exhalation.\nThe gas that is trapped (hyperinflating the lung) may rupture into the pleura (pneumothorax), mediastinum (pneumomediastinum), or pericardium (pneumopericardium). Slide 6 Surfactant dysfunction Meconium deactivates surfactant and may also inhibit surfactant synthesis. 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. Slide 7 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)-1β, IL-6, 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. Slide 8 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. \nPPHN 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. Slide 9 Etiology Factors that promote the passage of meconium in utero include: Placental insufficiency Maternal hypertension Preeclampsia Oligohydramnios Maternal drug abuse, especially of tobacco and cocaine Maternal infection/chorioamnionitis Fetal hypoxia Slide 10 Prognosis Most infants with meconium aspiration syndrome (MAS) have complete recovery of pulmonary function. MAS infants have a slightly increased incidence of respiratory infections in the first year of life because the lungs are still in recovery. Severely affected infants have an increased risk of developing reactive airway disease (RAD) in the first 6 months of life. Children with MAS may develop chronic lung disease from intense pulmonary intervention. Prenatal and intrapartum events that initiate the meconium passage may cause the infant to have long-term neurologic deficits, including central nervous system (CNS) damage, seizures, mental retardation, and cerebral palsy. Slide 11 Morbidity/mortality A large