Respiratory Distress In Term Infants: Meconium Aspiration

Question 1

Meconium is passed before birth by what percentage of babies?

Answer 1

8-20%

Question 2

Is it commonly or rarely passed by preterm infants?

Answer 2

Rarely

Question 3

It occurs increasingly with…

Answer 3

The greater the gestational age

Question 4

By 42 weeks it affects what percentage?

Answer 4

20-25%

Question 5

What can it be passed in response to?

Answer 5

Fetal hypoxia

Question 6

How does meconium impact the lungs?

Answer 6

It is a lung irritant
Causes both mechanical obstruction and a chemical pneumonitis
Can cause surfactant dysfunction
Can cause pulmonary vasoconstriction

Question 7

Meconium aspiration can predispose…

Answer 7

Infection

Question 8

What risk factors are there?

Answer 8

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

Question 9

Does it cause respiratory distress?

Answer 9

Yes it can - may be severe

Question 10

What is meconium?

Answer 10

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)

Question 11

MAS can cause respiratory distress and also exacerbate other neonatal complications such as…

Answer 11

Sepsis

Ischaemic insults

Question 12

Once meconium is aspirated, it can stimulate the release of…

Answer 12

Vasoactive and cytokines substances - activate inflammatory pathways and trigger vascular changes
It also can impact the effect of surfactant

Question 13

What are common features seen with MAS related respiratory distress?

Answer 13

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

Question 14

What symptoms are associated?

Answer 14

Tachypnoea
Tachycardia
Cyanosis
Grunting
Recessions 
Hypotension

Question 15

What investigations may be necessary?

Answer 15

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

Question 16

What will a CXR show?

Answer 16

Increased lung volumes
Asymmetrical patchy pulmonary opacities
Pleural effusions
Pneumothorax or Pneumomediastinum 
Multi focal consolidation due to chemical pneumonitis

Question 17

In MAS, there is a high incidence of air leak causing…

Answer 17

Pneumothorax

Pneumomediastinum

Question 18

What differentials are there?

Answer 18

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

Question 19

What does management of MAS depend on?

Answer 19

The severity of respiratory distress

Question 20

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?

Answer 20

No

Question 21

What management steps may be necessary?

Answer 21

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

Question 22

What complications can occur?

Answer 22

Pneumothorax or Pneumomediastinum
PPHN
CP - due to MAS leading to cerebral hypoxia
Chronic lung disease

Question 23

What is the leading cause of death in MAS?

Answer 23

PPHN