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Tony Liu, MD

MECONIUM ASPIRATION SYNDROME. Tony Liu, MD. MAS: Incidence. Incidence of meconium-stained amniotic fluid 8-20% of all deliveries Of those with MSAF, 1-9% develop MAS Term and postmature infants Presence in asphyxiated infants <34 weeks Unusual Possibly bilious reflux (obstruction)

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Tony Liu, MD

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  1. MECONIUM ASPIRATION SYNDROME Tony Liu, MD

  2. MAS: Incidence • Incidence of meconium-stained amniotic fluid • 8-20% of all deliveries • Of those with MSAF, 1-9% develop MAS • Term and postmature infants • Presence in asphyxiated infants <34 weeks • Unusual • Possibly bilious reflux (obstruction) • Purulent fluid (Listeria, Pseudomonas)

  3. MAS: Pathophysiology • Meconium- first intestinal discharge • Epithelial cells, fetal hair, mucus, bile • Intrauterine stress- passage into amniotic fluid, may be aspirated by the fetus when fetal gasping stimulated by hypoxia/hypercapnea • May cause airway obstruction • inflammatory response → respiratory distress • Presence of meconium in amniotic fluid can be a warning sign of fetal distress • Mothers- carefully monitored during labor

  4. Meconium- Epithelial cells, fetal hair, mucus, bile

  5. Pathophysiology: Meconium Passage In Utero • Exact mechanisms- unclear • Dependent on hormonal and parasympathetic neural maturation → peristalsis • Fetal distress, vagal stimulation- risk factors • Cord compression • After 34 weeks- incidence of meconium-staining increases from 1.6% (34-37 wks) to 30% (42 wks)

  6. Pathophysiology: Aspiration of Meconium • Aspiration occurs • After meconium passage, respiration/gasping • In utero, or during labor/delivery • Before delivery- aspiration impeded by viscous fluid normally filling the fetal lung • After delivery- lung fluid reabsorbed allowing distal progression of meconium

  7. Pathophysiology: MAS Early Consequences • Decreased lung compliance • Increased expiratory large airways resistance • Acute upper airway obstruction- progresses distally • Risk for total airway obstruction→ severe atelectasis • Areas of partial obstruction-ball-valvephenomenon • Air-trapping, hyperexpanded alveoli • Increases the risk of PTX 21-50%

  8. Pneumonitis Air Trapping

  9. Pathophysiology: MAS Early Consequences • Chemical Pneumonitis • Bronchiolar edema, small airways obstructed • Alveoli- surfactant inactivation, displacement from alveolar surface → atelectasis • CO2 retention, hypoxemia, VQ mismatch • Alveolar hypoxia, acidosis, hyperinflation • Pulmonary vascular resistance ↑ • R→L shunting, further hypoxemia

  10. MAS: Histology

  11. MAS Risk Factors • Postterm pregnancy • Preeclampsia-eclampsia • Maternal hypertension • Maternal diabetes mellitus • Abnormal fetal heart rate • IUGR • Abnormal biophysical profile • Oligohydramnios • Maternal conditions • Tobacco/cocaine, respiratory or CV disease

  12. MAS Clinical Presentation- Amniotic Fluid • Variable • Thin, green-stained fluid • Thick, dark "pea soup“ • Majority of infants with MAS

  13. “Pea Soup”

  14. MAS Clinical Presentation- The Infant • Variable presentation- amount/viscosity of aspirated meconium • Often normal outcome • Postmaturity common • SGA, long nails, peeling yellow/green stained skin • Risk for Erythema Toxicum, meconium- irritating • Respiratory distress- birth or transition period • Perinatal asphyxia • Respiratory depression • Hypotonia

  15. Clinical Presentation: Airway Obstruction • Airway obstruction- Early • Involve large airways • Sxs: apnea, gasping, poor air exchange, cyanosis • Airway must be rapidly cleared by ET suctioning • Airway obstruction- Late • Meconium driven distally to smaller airways • Air trapping • Scattered atelectasis

  16. Clinical Presentation • Respiratory distress- distal airway aspiration • ↑ Airway resistance, decreased compliance • Tachypnea, nasal flaring, intercostal retractions • Increased AP chest diameter • Delayed presentation- frequent • Initially- mild distress • Later- worsening distress: atelectasis, chemical pneumonitis develop • Auscultation: decreased air exchange, rales, rhonchi, wheezing • Green urine < 24 hrs after birth • Meconium pigment absorbed by the lung, excreted in urine

  17. Laboratory/Diagnostic Studies • Serum studies • ABG • Hypoxemia • Hyperventilation- mild cases • Hypoventilation- severe disease, respiratory acidosis (obstruction, atelectasis, pneumonitis) • Metabolic acidosis- in perinatal asphyxia • CXR • Hyperinflated lung fields, flattened diaphragms • Coarse, irregular patchy infiltrates • Pneumothorax, pneumomediastinum • *Often poorly correlates with clinical presentation

  18. Meconium Infiltrates Atelectasis

  19. Pneumothorax

  20. Diagnostic Studies: Echocardiogram Pulmonary Hypertension: R→L shunting Tricuspid Regurgitation

  21. MAS: Management Prenatally- Prevention is the best strategy: • Identification of high-risk pregnancies • Recognition of maternal factors in uteroplacental insufficiency and subsequent fetal hypoxia during labor • Monitoring during labor • Signs of fetal distress- loss of beat-to-beat variability, fetal tachycardia, deceleration patterns • Assessment by fetal scalp pH • If status compromised, corrective measures taken, timely delivery may be desired • Amnioinfusion- decreases MAS incidence/severity when moderate or thick meconium noted

  22. MAS- Delivery Room Management • Severity of MAS- markedly decreased by early removal of aspirated tracheal meconium (Gregory, 1974) • Hypopharyngeal suctioning- once head delivered, prior to spontaneous breathing • Infants- If not vigorous with thick, meconium-stained fluid should have endotracheal suctioning (3% of all deliveries) • 80-100 mmHg • Infants who are vigorous or with thin-moderate staining- controversial • If meconium suctioned “below cords”, consider repeating • *Use clinical judgment! NRP guidelines are unclear

  23. NRP Guidelines • “If the baby is not vigorous (Apgar 1-3): Suction the trachea soon after delivery (before many respirations have occurred) for ≤ 5 seconds. If no meconium retrieved, do not repeat intubation and suction. If meconium is retrieved and no bradycardia present, reintubate and suction. If the heart rate is low, administer PPV and consider repeat suctioning. “ • “If the baby is vigorous (Apgar >5): Clear secretions and meconium from the mouth/nose with a bulb syringe or a large-bore suction catheter. In either case, the remainder of the initial resuscitation: dry, stimulate, reposition, and administer oxygen as necessary.”

  24. Meconium Trap Aspirator -suction applied while ETT withdrawn

  25. Meconium Trap Aspirator

  26. MAS: Management • Pulmonary toilet- frequent suctioning of secretions,CPT • (Caution in persistent pulmonary hypertension) • ABG- arterial catheter for frequent sampling, BP monitoring • Oxygenmonitoring- differential pulse oximetry • Empiric Antibiotics • Meconium inhibits the bacteriostatic quality of AF • Meconium aspiration vs. pneumonia- difficult on CXR • Broad-spectrum, cultures • Supplemental O2 • Alveolar hypoxia → pulmonary vasoconstriction • Provide generously- Target PO2 ≥ 80-90 mmHg

  27. MAS Management: Mechanical Ventilation • Severe disease, respiratory failure • SIMV, HFOV • Higher inspiratory pressures- ↓lung compliance • Short TI allows adequate expiration when air trapping • High risk for Pneumothorax- consider if any acute deterioration • Goal: Achieve minimal pressure to provide adequate ventilation and oxygenation. • Surfactant– may help (detergent), risk of transient airway obstruction in the context of a labile infant

  28. Persistent Pulmonary Hypertension • Hypoxic pulmonary vasoconstriction • Abnormal muscularization of pulmonary microcirculation • Inhaled nitric oxide- selective vasodilator of pulmonary vasculature • Pressor support, fluid resuscitation • Correction of acidosis, hypoglycemia, hypocalcemia • Optimize nutrition • HFOV- Failing SIMV, can maximize the effects of inhaled NO • Lability- Cautious weaning, minimal handling, sedation • Perinatal asphyxia- surveillance of end-organ damage • Hepatic, renal failure, SIADH

  29. MAS Management: ECMO • Extracorporeal Membrane Oxygenation • Demonstrated failure of all therapies • Highly invasive • Survival 70-80% • Oxygenation Index > 40 with Paw >20 cmH2O may predict infants who will require ECMO • OI= (Fi02 x MAP x 100) / Pao2

  30. ECMO • Minimizes barotrauma • Allows lung to make surfactant • Allows aggressive suctioning • Supports heart • ECMO Survival 70%-80% • 40% if cardiac disease • CDH- worst prognosis, MAS- good • Supports 80% cardiac output.

  31. ECMO But: • Sacrifices neck vessels • No long term studies • And… • Heparin, bleeding • Catastrophes • BUBBLES = BAD! • Cavitation

  32. ECMO- Criteria • Severe C.P. disease that is REVERSIBLE • Failed medical tx for >96hrs • OI >25-60 for 30min-6hrs • Contraindications- • Trisomies , <34wks (IVH risk & small vessels), BW<2000g, coagulopathy, IVH • On vent >14d • Bad CHD

  33. Veno-Venous ECMO • VV ECMO: • Spares carotid artery • Preserves pulsatile flow • Avoids hyperoxia • Lungs and heart get Red blood • Avoid emboli into arterial side • Venous Tip- in R atrium • Does not give cardiac support • Partial re-circulation, and Lower PO2’s

  34. MAS: Prognosis • Newer modalities • High-frequency ventilation • Inhaled nitric oxide • ECMO • Exogenous surfactant • Have reduced the mortality to <5% • In survivors • BPD or CLD (prolonged mechanical ventilation) • Significant asphyxial insult, IVH- neurologic sequelae

  35. Meconium Dextrose, Candida, Influenza Camry, Mercedes, Crash, Wheel Emperor Millenium Apocalypse Timberland Orangejello, Lemonjello, Dijon Baby, Im Unique Samurai, Champion, Cal-El Vagina, Rectalina, Chlamydia, Yersenia Miracle, Special, Heaven, Destiny Real NICU Names(Need for Early Intervention) • Soowut • Meanttobe • Shithead (“Shi-thade”) • Bonus • Nevaeh, Semaj • White Cloud • Prescious Love • Earl Lee • Brook Lynne Bridges • Oshyn Cruz • Jack Daniels • Anita Mann • Donkey Ote

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