Edited May 2005

 Pulmonary Vascular Resistance
Ventilation
Remove
Placenta

Pulmonary Venous Return

LA Pressure
 PO
2
Foramen Ovale
Closes

RA Pressure

IVC Return

Umbilical Venous Return
L --> R ductus arteriosus shunt
 Systemic Vascular Resistance
Ductus
Venosus
Closes

 Meconium is the first intestinal discharge of the newborn
 Epithelial cells, fetal hair, mucus, bile
 Intrauterine stress may cause in utero passage of meconium
 Aspirated by the fetus when fetal gasping or deep breathing occurs stimulated by hypoxia and hypercarbia
 Warning sign of fetal distress

Meconium: The Stats



Frequency of Mec stained amniotic fluid = 10-25%
OF MEC stained infants:
 30 % depressed at birth
 10 % meconium aspiration syndrome (range 2-36 %)
OF infants with MEC aspiration syndrome
 17 % deliver through thin meconium (range 7-35 %)
 35 % need mechanical ventilation (range 25-60 %)
 12 % die (range 5-37 %)

OHSU Experience: Inborn + Transfers
# Mec passed
1992-94 146
1995-97 154
DR intub
MAS MAS
+ vent
88 44
92 39
28
25
ECMO Died
4
1
3*
1*
Total 300 180 83 53 5 4
MAS = Meconium aspiration syndrome as primary pulmonary diagnosis
No pulmonary hypoplasia or major congenital anomalies
MAS+ vent = ventilated with pulmonary diagnosis of MAS or PPHN
ECMO = MAS infants transferred for ECMO
Died : * 1 infant in each of the years died with a diagnosis of severe HIE

 Postterm pregnancy
 Preeclampsia-eclampsia
 Maternal hypertension
 Maternal diabetes mellitus
 Abnormal fetal heart rate
 IUGR
 Abnormal biophysical profile
 Oligohydramnios
 Maternal heavy smoking

Meconium in Amniotic Fluid
Intrapartum suctioning of mouth, nose, pharynx
Infant Depressed
Infant Active
Observe
Intubate and suction trachea
Other resuscitation as indicated

Meconium Aspiration Syndrome
Pathophysiology
 Airway obstruction of large and small airways
 Inflammation and edema
 Protein leak
 Inflammatory Mediators
 Direct toxicity of meconium constituents = chemical pneumonitis
 Surfactant dysfunction or inactivation
 Effects of in utero hypoxemia and acidosis
 Altered pulmonary vasoreactivity (PPHN)

Meconium Aspiration Syndrome
Diagnosis
 Known exposure to meconium stained amniotic fluid
 Respiratory symptoms not explained by other cause
 R/O pneumonia, RDS, spontaneous air leak
 CXR changes - diffuse, patchy infiltrates, consolidation, atelectasis, air leaks, hyperinflation


Ventilation strategies
 Avoid air leak, check CXR with acute deterioration
 Prevent pulmonary hypertension - generous O2
 HFOV if unable to maintain on conventional vent
 Steroids (no human data, controversial)
 ROS, Antibiotics (ampicillin, gentamicin)
 Surfactant
 Inhaled Nitric Oxide
 ECMO

 Hypoxia
 Acidosis
 Hypoglycemia
 Hypocalcemia
 End-organ damage due to perinatal asphyxia

 High incidence long term pulmonary problems
 At 6 months - 23% MAS with regular bronchodilator therapy*
 FRC was higher in symptomatic infants
 IPPV and O2 were not predictors of problems
 Increased risk of poor neurologic outcome due to perinatal insult - seizures, CP, mental retardation
*Yuksel et al. Pediatric Pulmonology 16:358, 1993

Meconium Aspiration Syndrome
Surfactant Treatment
Methods
 < 6 hours old with MAS
 20 infants randomized to receive 150 mg/kg surfactant by 20 minute infusion, q6h x4 doses maximum
 On ventilator - FiO
2
> 50%, MAP > 7, a:A PO
2
< 0.22
 Endpoint = improvement in OI and a:A PO
2
 No difference in groups
Findlay et al. Pediatrics 97 (1): 48, 1996.

Meconium Aspiration Syndrome
Surfactant Treatment
Results
 No infant received more than 3 doses
 Significant improvement in OI, MAP, FiO
2 within 3-6 hours after 2 nd dose of surfactant
 Significant improvement in a:A PO
2 within 1 hour of 1 st dose of surfactant
Findlay et al. Pediatrics 97 (1): 48, 1996.

Meconium Aspiration Syndrome
Surfactant Treatment
Air leak
ECMO
Days MV
Days O
2
LOS (days)
D/C on O
2
Mortality (< 28 d)
Control Surf P value
5 0 0.024
6 1 0.037
11 (1) 8 (1) 0.047
20 (3) 13 (1) 0.031
24 (2) 16 (1) 0.003
8 6 NS
0 0 NS
Findlay et al. Pediatrics 97 (1): 48, 1996.