Meconium aspiration

Question 1

Define meconium aspiration.

Answer 1

Respiratory distress in the neonate secondary to passage of meconium (fetal intestinal contents) stained amniotic fluid into the respiratory system.

Question 2

Explain the aetiology/risk factors of meconium aspiration.

Answer 2

Fetal hypoxic stress -> in utero meconium passage from neural stimulation of a mature GI tract. Head or cord compression may also cause peristalsis and relaxation of the anal sphincter.

Meconium is rarely found in the amniotic fluid <34/40. Meconium-stained fluid may be aspirated into the lungs, causing obstruction and chemical pneumonitis. The passage of meconium becomes increasingly common the greater the infant’s gestational age, particularly when post-term.

Question 3

Summarise the epidemiology of meconium aspiration.

Answer 3

Meconium staining: 10–15% live births; of these, 1–9% experience meconium aspiration syndrome

Question 4

What are signs and symptoms of meconium aspiration?

Answer 4

Fetal tachycardia, bradycardia or absence of fetal accelerations on cardiotocography in utero identifies high-risk infant. At birth the neonate may exhibit signs of postmaturity with evidence of weight loss and heavily stained yellow nails, skin and umbilical cord.

Question 5

What are signs and symptoms of respiratory distress?

Answer 5

Diagnosed at birth, or within 4 hours; consists of tachypnoea, tachycardia, recession; intercostal/subcostal/sternal/substernal, nasal flaring, grunting in respiration against a partially closed glottis, harsh diminished breath sounds, chest may has a overinflated appearance (due to air trapping). In severe cases the neonate may become cyanosed.

Question 6

What are appropriate investigations for meconium aspiration?

Answer 6

Chest X-ray: Hyperinflation, flattening of diaphragm, cardiomegaly, gross patchy shadowing.

Blood gas: Reduced pO2

Question 7

What is the management for meconium aspiration?

Answer 7

Neonates born through meconium stained liquor require a paediatrician to be present at birth. May require neonatal resuscitation if not breathing.

Good condition: No further management.

Poor condition: Airway suction under direct vision, directly/via an ET tube/meconium aspirator. +/- intermittent positive airway ventilation.

Subsequent management on NICU: Supportive respiratory therapy with antibiotics, ventilatory assistance, exogenous surfactant therapy. Inhalation of nitric oxide and extracorporeal membrane oxygenation (ECMO) may be required.

Question 8

What is the prognosis for meconium aspiration?

Answer 8

Depends on hypoxic insult.

Question 9

How does meconium aspiration cause mechanical obstruction and what is the outcome of this?

Answer 9

Air trapping/hyperdistention of alveoli

Rupture - pneumothorax/pneumomediastinum/pneumopericardium

Respiratory acidosis and primary/secondary presistent pulmonary hypertension of the newborn

Question 10

How does meconium aspiration cause chemical pneumonitis and what is the outcome of this?

Answer 10

Release of cytokines (TNF-alpha and IL1beta/6/8/13)

Diffuse pneumonia

Respiratory acidosis and primary/secondary presistent pulmonary hypertension of the newborn

Question 11

How does meconium aspiration cause surfactant dysfunction and what is the outcome of this?

Answer 11

Minimal surface tension - diffuse atelectasis

Respiratory acidosis and primary/secondary presistent pulmonary hypertension of the newborn