mas

1. Tony Liu, MD
MECONIUM ASPIRATION
SYNDROME

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)

4. 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

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

6. 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)

7. 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

8. 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-valve phenomenon
 Air-trapping, hyperexpanded alveoli
 Increases the risk of PTX 21-50%

9. Pneumonitis Air Trapping

10. 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

12. MAS: Histology

13. 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

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

15. “Pea Soup”

16. 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

17. 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

18. 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

19. 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

20. Meconium Infiltrates Atelectasis

21. Pneumothorax

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

23. 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

24. 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

25. 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.”

26. Meconium Trap Aspirator
-suction applied while ETT withdrawn

27. Meconium Trap Aspirator

28. MAS: Management
 Pulmonary toilet- frequent suctioning of secretions, CPT
 (Caution in persistent pulmonary hypertension)
 ABG- arterial catheter for frequent sampling, BP monitoring
 Oxygen monitoring- 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

29. 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

30. 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

31. 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

32. 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.

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

34. 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

35. 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

39. 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

40. Real NICU Names
(Need for Early Intervention)
 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
•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