Meconium Aspiration

What on earth is meconium, anyway?
The first intestinal discharge of the newborn, made up of:
1)epithelial cells 2)fetal hair 3)mucus 4)bile

While usually passed out by the newborn within 48 hours of birth, intrauterine stress may cause inutero passage of meconium into the amniotic fluid, and is a warning sign of fetal distress. As one can imagine then, accidental aspiration of meconium must not be very pleasant.

Aesthetics aside, meconium aspiration causes airway obstruction and intense inflammatory reaction resulting in severe respiratory distress.

Happening in mostly term and postterm infants, risk factors for meconium aspiration include:
1)postterm pregnancy 2)abnormal fetal heart rate 3)preeclampsia-eclampsia
4)maternal hypertension 5)maternal diabetes mellitus 6)SGA infants 7)biophysical profile =<6 8)Maternal heavy smoking, chronic respiratory disease, or cardiovascular disease

Pathophysiology (why and how it happens):
Caused namely by asphyxia and other forms of fetal stress, we see an increase in intestinal peristalsis, coupled with relaxation of the external anal sphincter, leading to passage of meconium.

What happens next:
Upon aspiration of meconium, airway obstruction and chemical pneumonitis ensues:

AIRWAY OBSTRUCTION:
Comes in the form of total and partial obstruction.
Total obstruction leads to atelectasis and Partial obstruction results in airtrapping and hyperexpansion (increasing risk of air leak)

CHEMICAL PNEUMONITIS:
Bronchiolar edema and narrowing of the small airways resulting in uneven ventilation. Areas of partial obstruction and superimposed pneumonitis causes severe CO2 retention and hypoxemia. This causes increase in pulmonary vascular resistance.