11/14/24, 10\:55 AM Meconium Aspiration Syndrome

Meconium Aspiration Syndrome

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Meconium aspiration syndrome (MAS)\: spectrum of respiratory distress in neonates born through meconium-stained
liquor.
Clinical presentation\: varies from mild respiratory distress to severe respiratory failure, not explained by an alternative
diagnosis.
Aetiology\: Meconium is sterile but can stimulate an in
cytokine release.
Risk factors\: 2-10% of neonates with meconium-stained liquor develop MAS. Higher risk with postdates gestation and small
for gestational age.
Clinical features\: Meconium-stained liquor, respiratory distress at birth, hyperin
consolidation on chest X-ray, increased oxygen requirements.
Respiratory e
lead to pneumothorax due to airway obstruction.
Di
pneumothorax, hypovolaemia.
Investigations\: Pre- and post-ductal saturations, capillary/venous gas, FBC, CRP, blood cultures, chest X-ray
(hyperin
Management\:
Preventative\: Prevent fetal hypoxia, avoid postdates gestation.
At delivery\: Vigorous infants need no oropharyngeal suctioning; non-vigorous infants may need oropharyngeal suctioning if
the airway is obstructed.
Post-delivery\: Asymptomatic infants with APGAR >9 need sepsis monitoring; symptomatic infants require admission to
neonatal unit.
Supportive care\: Oxygen therapy, assisted ventilation, cautious CPAP use, possible sedation, surfactant therapy, ECMO for
severe cases, antibiotics while awaiting culture results.
Complications\: Most infants recover well. Short-term\: ongoing oxygen needs, seizures, necrotising enterocolitis. Long-
term\: potential increased risk of reactive airways disease, limited evidence for altered neurodevelopment.
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Introduction

Meconium aspiration syndrome (MAS) refers to a varying spectrum of respiratory distress in neonates born through
meconium-stained liquor.
The clinical presentation can vary from mild respiratory distress through to severe respiratory failure, which cannot be
explained by an alternative diagnosis.
1
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Aetiology

Meconium is the
vernix and amniotic
Although meconium is sterile, if it enters the respiratory tract can stimulate an in
release.
The release of meconium into the amniotic
compression or hypoxia) which may accompany the clinical picture of MAS.
1

Risk factors

Approximately 2-10% of neonates born through meconium-stained liquor will develop MAS.
Meconium-stained liquor (and therefore MAS risk) increases with postdates gestation and small for gestational age.
1

Clinical features

The diagnosis of MAS is made based on the following clinical features\:
1,5
Meconium-stained liquor
Respiratory distress at or shortly following birth
Typical radiographic features on chest X-ray\: hyperin
Increased oxygen requirements (mechanical ventilation may be required for severe cases)
Meconium can a
1
Respiratory distress\: meconium has been shown to have a damaging e
result in severe e
reduced compliance and reduced oxygenation.
Pneumonitis\: meconium can lead to irritation and local in
pneumonitis.
Bacterial pneumonia\: meconium-stained liquor is a known risk factor for bacterial infection in utero (E s c h e r i c h i a c o l i in
particular), leading to potentially increased morbidity.
Pneumothorax\: the meconium, if thick, can cause airway obstruction in distal small airways. Meconium plugging and
distal gas trapping can lead to distention of distal lung and pneumothorax.
Ultimately, all of the above mechanisms lead to hypoxia and respiratory distress.

Di

Di
These include transient tachypnoea of the newborn (TTN), delayed transition from fetal circulation, sepsis, congenital
pneumonia, persistent pulmonary hypertension of the newborn (PPHN), pneumothorax and hypovolaemia.
1
These di
1
Infants with TTN may initially present in a similar way to MAS, however, they are quick to recover
Pneumonia can be di
return
Pneumothorax is di

Investigations

Bedside investigations

Relevant bedside investigations include\:
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Pre- and post-ductal saturations\: to assess respiratory involvement and detect congenital cardiac lesions
Capillary gas or venous gas\: to assess the degree of respiratory compromise and assist in decisions regarding respiratory
support and systemic involvement

Laboratory investigations

Relevant laboratory investigations include\:
Full blood count\: to look for raised white cell count suggestive of an infective process
CRP\: to look for an infective process
Blood cultures\: to look for bacteraemia suggestive of sepsis and/or pneumonia

Imaging

A chest X-ray should be performed according to local guidelines. Some neonatal units would consider waiting four hours
to perform a chest X-ray. This time would be su
1
However, if the infant is acutely unwell or mechanically ventilated, delaying a chest X-ray is not an option.
Chest X-ray
show pneumothorax or pneumomediastinum due to raised alveolar tension.
5
The X-ray also helps di

Management

Preventative management

There are several preventatives measures to take at various stages of delivery to prevent meconium aspiration syndrome.
3
Intrapartum measures include prevention of fetal hypoxia and prevention of postdates gestation.
For infants who are born through meconium-stained liquor, management at time of delivery depends on the clinical status
of the infant.
A vigorous infant requires no oropharyngeal suctioning despite the meconium-stained liquor as this does not reduce the
risk of meconium aspiration syndrome.
2
A non-vigorous infant should not have routine endotracheal suction for meconium. However, these infants may require
oropharyngeal suctioning if there is meconium obstructing the airway. The priority should be to rapidly initiate ventilation.
2

Post-delivery

Asymptomatic infants with an APGAR score of >9 do not require additional monitoring, other than that of risk of sepsis
monitoring given the increased risk of infection with meconium aspiration.
3
Infants with respiratory distress after birth should be admitted to a neonatal unit for 4-6 hours to ensure a successful
transition.
3
Management is supportive to avoid morbidity and mortality associated with MAS.
Supportive management includes oxygen therapy as needed, assisted ventilation if required. Continuous positive airway
pressure (CPAP) is used with caution as this may exacerbate air trapping.
Some infants may require sedation (if ventilated) and surfactant therapy may reduce the need for extracorporeal
membrane oxygenation (ECMO) in ventilated infants. However, ECMO may be required for severe cases.
3
Antibiotics are usually started whilst awaiting blood cultures results. The risk of not treating an infection is signi
can often be di
3

Complications

Most infants with MAS have a good outcome and are discharged home. Short-term complications include ongoing oxygen
requirements, seizures, and necrotising enterocolitis.
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Some studies have suggested an increased incidence of reactive airways disease in infants who had MAS. There is limited
evidence for altered neurodevelopment in infants who had MAS.
3

References

UpToDate. C l i n i c a l F e a t u r e s a n d D i a g n o s i s o f M e c o n i u m A s p i r a t i o n S y n d r o m e . Published Aug 12, 2019. Available from\: ANZCOR (Australia New Zealand Council of Resuscitation). A N Z C O R G u i d e l i n e 1 3 .4 – A i r w a y M a n a g e m e n t a n d M a s k
V e n t i l a t i o n o f t h e N e w b o r n I n f a n t . Available from\: [LINK]
[LINK]
UpToDate. P r e v e n t i o n a n d M a n a g e m e n t o f M e c o n i u m A s p i r a t i o n S y n d r o m e . Published Jan 7, 2020. Available from\: [LINK]
Pandita, A., Murki, S., Oleti, T., Tandur, B., Kiran, S., Narkhede, S. and Prajapati, A., 2018. E
Airway Pressure on Infants With Meconium Aspiration Syndrome. J A M A P e d i a t r i c s , 172(2), p.161.
Bickle, I., Radswiki et al. M e c o n i u m A s p i r a t i o n . Available from\: [LINK]

Reviewer

Dr Thuy-Tien Vo
Paediatric Registrar

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Contents

Introduction
Aetiology
Risk factors
Clinical features
Di
Investigations
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