Epidemiology

Incidence

• 13% all live births.^[1]
• Fewer than 5% of deliveries below 37 completed weeks have meconium staining.^[2]

Risk factors

• Placental insufficiency
• Maternal hypertension and pre-eclampsia
• Oligohydramnios
• Smoking
• Cocaine abuse

Management

These recommendations are from the National Institute for Health and Clinical Excellence (NICE) (2007).^[3]

Intrapartum

• If significant meconium staining is noted in labour, there should be continuous electronic fetal monitoring.
• If there are signs of fetal distress, a fetal blood sample should be obtained. If pH is <7.21, there should be emergency delivery.
• Ensure that the advanced resuscitation unit and appropriately trained staff are available.
• There should be no suction prior to delivery.

At delivery - healthy neonate

• If the baby is in good condition, (Apgar score >5, based on colour, tone, heart rate and breathing) there should be no suction.
• The baby should be observed for signs of respiratory distress in the first hour of life, 2nd hour and then 2-hourly until 12 hours old.
• If there is blood or if there are lumps of meconium in the oropharynx, suction should be used in the upper airways.
• In a Cochrane review routine endotracheal intubation at birth in otherwise healthy, term meconium-stained babies, was not shown to be superior to routine resuscitation including oropharyngeal suction.^[4]

At delivery - sick neonate

• If the baby's vital signs are depressed, suction should be carried out under direct vision.
• Admission to the intensive care unit should be accompanied by:
  • CXR
  • FBC, U&E
  • Arterial blood gases
• Antibiotics are not routinely given.
• Research has not shown any one form of ventilation to be superior to others, but strategies that recruit alveoli are desirable:
  • Surfactant lavage or replacement is beneficial in the treatment of established respiratory distress. In infants with meconium aspiration syndrome (MAS), surfactant administration may reduce the severity of respiratory illness and decrease the number of infants with progressive respiratory failure requiring support with extracorporeal membrane oxygenation (ECMO).^[5]
  • Natural surfactant has a more rapid onset.
  • Nitric oxide (NO) inhalation improves oxygenation in some infants with persistent pulmonary hypertension (PPHN). NO reduces the use of ECMO.^[6]
  • ECMO is a complex and expensive technique. It is effective for mature newborn infants (more than 35 weeks' gestation and more than 2 kg) with severe respiratory failure.

Complications

Neonatal respiratory distress syndrome

• This is respiratory distress that usually occurs within 4 hours of birth and becomes persistently worse for 48 to 72 hours. If not fatal, it resolves by 72 hours.
• A deficiency of surfactant produces high alveolar surface tension. The baby must reinflate the collapsed alveoli with every breath. Thus, every breath takes a lot of effort for relatively poor expansion.
• Surfactant replacement therapy has shortened the duration of the disease and significantly reduced mortality. It is treated with administration of synthetic or animal surfactant.

Persistent pulmonary hypertension of the newborn

• Babies may suffer from persistent pulmonary hypertension of the newborn, as a consequence.
• This is where the fetal circulation persists with blood being shunted away from the lungs through the foramen ovale and a patent ductus arteriosus.
• It is a consequence of raised pulmonary vascular resistance. Clinical features include cyanosis, tachypnoea and the murmur of patent ductus arteriosus.

Treatment includes:

• Supportive measures, including ventilation
• Prostacyclin infusion
• Extracorporeal membrane oxygenation (ECMO)

Chronic lung disease

• Children with meconium aspiration may develop chronic lung disease as a result of intense pulmonary intervention.
• Infants with meconium aspiration have a slightly increased incidence of infections in the first year of life because the lungs are still in recovery.

Prognosis

• Up to 10% of cases of meconium staining develop meconium aspiration syndrome (MAS).^[7]
• Nearly all infants with MAS have complete recovery of pulmonary function.
• Initial hypoxic events may cause the infant to have long-term neurological problems, including seizures, mental retardation and cerebral palsy.

Prevention

Avoidance of risk factors mentioned above. Meconium aspiration syndrome (MAS) can be reduced by:

• Avoiding postmaturity.^[8] Antenatal monitoring beyond 42 weeks reduces perinatal mortality, but is inefficient in reducing meconium-stained liquor seen with increasing gestation.^[9]
• Careful fetal monitoring.
• Appropriate use of Caesarean section.^[8]

Amnioinfusion

• This aims to prevent or relieve umbilical cord compression during labour, by infusing a 250-500 ml bolus of warmed normal saline through a double lumen intrauterine pressure catheter. Uterine pressure and fetal heart rate (via scalp electrode) are monitored constantly.
• It is also thought to dilute meconium and so reduce the risk of meconium aspiration.^[10]
• However, it may work by correcting oligohydramnios, with the maintenance infusion aiming to give an amniotic pool depth of 8-12 cm.
• Evidence is conflicting. The New England Journal of Medicine (NEJM) found that amnioinfusion did not reduce the risk of moderate or severe meconium aspiration syndrome, perinatal death, or other major maternal or neonatal disorders in women who had thick meconium staining in the amniotic fluid.^[11] The evidence is more positive in settings with less than standard perinatal surveillance methods.^[12] The potential adverse effects include umbilical cord prolapse, uterine scar rupture and amniotic fluid embolism. NICE does not recommend its use.