Respiratory Distress In Term Infants: Meconium Aspiration Flashcards
Meconium is passed before birth by what percentage of babies?
8-20%
Is it commonly or rarely passed by preterm infants?
Rarely
It occurs increasingly with…
The greater the gestational age
By 42 weeks it affects what percentage?
20-25%
What can it be passed in response to?
Fetal hypoxia
How does meconium impact the lungs?
It is a lung irritant
Causes both mechanical obstruction and a chemical pneumonitis
Can cause surfactant dysfunction
Can cause pulmonary vasoconstriction
Meconium aspiration can predispose…
Infection
What risk factors are there?
Intrapartum hypoxia Foetal distress Gestational age >42 Maternal HTN Maternal DM Pre eclampsia or eclampsia Maternal smoking/substance abuse IUGR Chorioamnionitis+/- prolonged pre rupture Oligohydramnios Apgar score less than 7 Thick meconium particles
Does it cause respiratory distress?
Yes it can - may be severe
What is meconium?
Dark green, sticky and lumpy faecal material produced during pregnancy
Usually released after birth, but baby can pass it in utero leading to meconium stained amniotic fluid (MSAF)
- babies can aspirate MSAF and develop meconium aspiration syndrome (MAS)
MAS can cause respiratory distress and also exacerbate other neonatal complications such as…
Sepsis
Ischaemic insults
Once meconium is aspirated, it can stimulate the release of…
Vasoactive and cytokines substances - activate inflammatory pathways and trigger vascular changes
It also can impact the effect of surfactant
What are common features seen with MAS related respiratory distress?
Partial or total airway obstruction - decreased pulmonary ventilation or small airways, which can cause atelectasis and air trapping. Pulmonary pressure increasing causing R to L shunt (through PDA/FO)
Foetal hypoxia - due to variety of factors e.g increased pulmonary vascular pressures, mechanical obstruction, airway oedema, surfactant inactivation
Pulmonary inflammation
Infection - inflammatory process predisposes to infection, meconium is sterile but provides a good medium for bacteria growth
Surfactant inactivation
Persistent pulmonary hypertension - remodelling of vascular bed in response to hypoxia
What symptoms are associated?
Tachypnoea Tachycardia Cyanosis Grunting Recessions Hypotension
What investigations may be necessary?
CXR
Infection markers - FBC, CRP, blood cultures
Arterial blood gas
Dual pulse oximetry - determine hypoxia, assess any potential R to L shunts
ECHO - to exclude CHD causing pulmonary HTN
Cranial USS - assess for results of any hypoxic brain damage
What will a CXR show?
Increased lung volumes Asymmetrical patchy pulmonary opacities Pleural effusions Pneumothorax or Pneumomediastinum Multi focal consolidation due to chemical pneumonitis
In MAS, there is a high incidence of air leak causing…
Pneumothorax
Pneumomediastinum
What differentials are there?
Transient tachypnoea of the newborn
RDS - but more common in preterm infants
Persistent pulmonary hypertension
Pneumothorax- May occur spontaneously in up to 2% of deliveries
Pneumonia
What does management of MAS depend on?
The severity of respiratory distress
Is there evidence that aspiration of meconium from infants oropharynx immediately after head delivery or removal by intubation and tracheal suctioning after birth, reduces incidence or severity of MAS?
No
What management steps may be necessary?
Observations for respiratory distress, close watch of saturations
Routine care: keep warm as hypothermia inhibits surfactant production, nutritional support - IV fluids and switch to NG when permitting
Ventilation/ oxygen therapy - via nasal cannula, CPAP or intubated and mechanically ventilated
Antibiotics - if infection suspicion
Surfactant bolus if moderate MAS or pneumothorax
Inhaled nitric oxide - for pulmonary HTN
What complications can occur?
Pneumothorax or Pneumomediastinum
PPHN
CP - due to MAS leading to cerebral hypoxia
Chronic lung disease
What is the leading cause of death in MAS?
PPHN
