Meconium Aspiration Flashcards
What is meconium?
the first feces or stool of the newborn
- is the dark green, sticky and lumpy faecal material produced during pregnancy and released from the bowels after birth
What is meconium aspiration syndrome?
is the term used to describe a spectrum of disorders, marked by various degrees of respiratory distress in the new born infant
- This follows the aspiration of meconium stained amniotic fluid (MSAF)
Meconium stained amniotic fluid is a result of?
is the after-effect of in-utero peristalsis
- In term or post term infants, where gastrointestinal maturation is appropriate, this movement leads to meconium passage
Peristalsis in utero that causes MSAF is usually the result of?
- foetal hypoxic stress
- vagal stimulation due to cord compression
- chronic hypoxia
Note: these factors can also lead to fetal gasping which results in MAS.
Common features seen with meconium aspiration syndrome related respiratory distress of the newborn?
- partial or total airway obstruction
- foetal hypoxia
- pulmonary inflammation
- infection
- surfactant inactivation
- persistent pulmonary hypertension
- all contribute to and cause lung injury leading to foetal hypoxia and respiratory distress
Clinical features of MAS?
- Meconium-stained amniotic fluid
- Respiratory distress at or shortly following birth
- Typical radiographic features on chest X-ray
- hyperinflation
- patchy opacification
- consolidation - Increased oxygen requirements (mechanical ventilation may be required for severe cases)
How does meconium affect the respiratory system?
- respiratory distress
- pneumonitis
- bacterial pneumonia
- pneumothorax
- all lead to hypoxia and respiratory distress
How does meconium aspiration cause respiratory distress?
damaging effect on surfactant and its metabolism
- This can result in severe effects related to reduced surfactant including:
1. increased surface tension
2. reduced lung volume
3. reduced compliance
4. reduced oxygenation
How does meconium aspiration cause pneumonitis?
meconium can lead to irritation and local inflammation resulting in exudative and inflammatory pneumonitis
How does meconium aspiration cause bacterial pneumonia?
meconium-stained amniotic fluid is a known risk factor for bacterial infection in utero (Escherichia coli in particular), leading to potentially increased morbidity
How does meconium aspiration cause 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
Differential diagnoses of MAS and how they can be distinguished from it?
- transient tachypnoea of the newborn (TTN)
- Infants with TTN may initially present in a similar way to MAS, however, they are quick to recover - delayed transition from fetal circulation
- sepsis
- congenital pneumonia
- Pneumonia can be difficult to differentiate initially and infants will be treated with antibiotics until blood culture results return - persistent pulmonary hypertension of the newborn (PPHN)
- pneumothorax
- Pneumothorax is differentiated with transillumination of the chest wall and a chest X-ray - hypovolaemia
Lab investigations for MAS?
- 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 of MAS?
Chest X-ray findings in MAS may show hyperinflated lungs due to distal air trapping, patchy pulmonary changes and may show pneumothorax or pneumomediastinum due to raised alveolar tension
