Disease Process of Neonatal Abstinence Syndrome

The exact cause of Neonatal Abstinence Syndrome is the sudden discontinuation of infant exposure of to substances that were used by mothers during pregnancy. The most common substance that causes NAS is opioids such as heroin, codeine, oxycodone, methadone, or buprenorphine. Birth initiates the cessation from whatever substance is being used by the mother and allows the onset of a dangerous withdrawal period.

Figure 1. Transfer of opioids across the placenta 

(Neonatal Abstinence Syndrome, 2010).

The pathophysiology of NAS is not completely understood, but it definitely involves multiple body systems and could have still unknown effects on the long-term health and quality of life of the infant. The drug substance makes its entry into the bloodstream of the newborn via the placenta (Figure 1). Opiates are water soluble, low molecular weight substances that can easily cross this otherwise protective barrier between the bloodstream of the mother and fetus. As the fetus grows and demands more nutrients from mom, this transfer of opioids increases.

Figure 2. Mechanism of opioid withdrawal in neonates (Kocherlakota, 2014)

All opioids act primarily on opioid receptors in the central nervous system, peripheral nervous system, and the gastrointestinal system among others. As the substance abuse continues throughout birth, the fetus's body becomes accustomed to this receptor stimulation. When the stimulation of these opioid receptors is abruptly stopped by birth, a chain reaction is triggered in the newborn body. 

The absence of opioids triggers the production of norepinepherine, acetylcholine and corticotrophin. Additionally, the production of dopamine decreases during this withdrawal period. The ability of the autonomic and peripheral nervous systems and the gastrointestinal system to work properly is also affected after extended exposure to the opioids. See a complete diagram explaining the cascade to the left (Figure 2). Next week's blog will discuss how these different neurotransmitter and hormone changes cause dangerous responses in the newborn. 

References

Kocherlakota, P. (2014). Neonatal Abstinence Syndrome. Pediatrics, 134(2), 547-561. doi: 10.1542/peds.2013-3524. 

Neonatal Abstinence Syndrome. (2010). Retrieved from http://images.walgreens.com/marketing/library/contents.jsp?docid=19888&doctype=2