Meconium Stained Liquor and Aspiration

Meconium is, effectively, the earliest stool of the infant.  It is a green liquid substance consisting of bile, dead epithelial cells, lanugo, mucus and amniotic fluid.

• Meconium is usually first passed after delivery, but can be passed in utero.
  • This occurs in up to 13% of all live births.  Rarely occurs in preterm babies.
    • Up to 10% of these babies (i.e. with staining) develop aspiration.
  • Most of these babies won’t have any major complications (the majority fully recover within 7-14 days).  However, aspiration of meconium can cause serious complications due to
    • obstruction of the airways
    • surfactant dysfunction
    • chemical pneumonitis
    • pulmonary hypertension
  • Rarely, initial hypoxic events can cause permanent neurological damage and respiratory interventions early in life can lead to permanent chronic lung disease (see Bronchopulmonary dysplasia)

Pathogenesis

• Meconium passage generally can’t occur in infants <34 weeks as meconium has not had time to reach the distal colon.  Passage is thought to occur due to peristalsis and sphincter relaxation secondary to a number of possible underlying causes
  • Increased concentrations of motilin
  • Infection
  • hypoxia
  • vagal stimulation secondary to cord compression
    • NB Many babies don’t appear to have any of these features
• Meconium aspiration, in utero, is usually a consequence of hypoxia-induced gasping
  • Once aspirated, meconium quickly migrates to the peripheral lungs (either as a result of PAP or spontaneously)
    • It then blocks the airway, leading to hyperaeration or atelectasis of the airway.
    • Meconium also sets up an inflammatory process until it is eventually cleared by macrophages
• Meconium Aspiration Syndrome has five major components

1. Airway obstruction
   1. As above, may lead to atelectasis and even rupture of the membranes- pneumothorax and/or interstitial emphysema
2. Pulmonary Vasoconstriction and Persistent Pumonary Hypertension of the Newborn (PPHN)
   1. Often accompanied by right to left shunting caused by increased pulmonary vascular resistance- usually a PFO or PDA
   2. PPHN could be caused by
      1. hypertrophy or neomuscularisation of past-acinar capillaries as a result of chronic intra-uterin hypoxia
      2. pulmonary vasoconstriction as a result of hypoxia, hypercarbia, or acidosis
      3. pulmonary vasoconstriction as a result of inflammation
   3. Usually resolves within 3-4 days if the infant recovers well
3. Surfactant Dysfunction
   1. Meconium is thought to inactivate surfactant function
4. Infection
   1. Meconium is a good bacterial growth medium, particularly for group B strep
5. Clinical Pneumonitis

Risk factors

• Placental insufficiency
• Maternal hypertension and pre-eclampsia
• Oligohydramnios
• Smoking
• Drug abuse
• Caesarean section

Presentation

• Green, meconium stained liquor (at rupture of membranes)
  • This can be light or more heavily stained and dark
• Green/blue staining of the skin at birth
• At birth the baby may appear limp with a low APGAR score.  They may also show signs of respiratory distress
• If the baby is postmature, there may be signs such as skin peeling
• The baby may also be bradycardic

Monitoring and Treatment

• Continuous electro-foetal monitoring should be used in women with significant meconium staining and considered in women with mild staining (depending on risk evaluation based on stage of labour, volume of liquor, parity, foetal heart rate)
  • Amnioinfusion (infusion of saline into the amniotic cavity- aim to relieve umbilical cord compression, dilute meconium and rectify oligohydramnios) is NOT recommended by NICE.
  • Consider induction of labour if there are any signs of foetal distress
• Once delivered
  • Basic life support, including suction of meconium from the oropharynx, should be performed if necessary
  • Babies with an APGAR score >5 who are otherwise healthy just require regular (2-hourly for the first 12 hours, at least) observation for
    • general well-being
    • chest movements/nasal flare
    • Skin colour/perfusion (inc cap refill)
    • feeding
    • muscle tone
    • temperature
    • HR and RR
  • If the baby has depressed vital signs, laryngoscopy and suction may be required
  • If the baby has an APGAR <5 at 10 mins, more intensive management (including intubation if required) should be considered
• Management of RDS (surfactant and sometimes steroids) and PPHN (mainly O2 support, occasionally steroids, but extra-corporeal membrane oxygenation is an advanced technique used in severe cases)
• Management of any infection