Neonatal abstinence syndrome (NAS) is a neurobehavioral disorder in neonates born to mothers with substance use and abuse during pregnancy, most commonly secondary to opioid use. The exact pathophysiology of neonatal abstinence syndrome is incompletely understood, but genetic susceptibility, maternal-fetal-placental pharmacokinetics, changes in receptor sensitivity, and neurotransmitter dysregulation seem to play roles.
Neonatal abstinence syndrome is characterized by withdrawal symptoms after birth when the exposure to the substance is terminated. Withdrawal symptoms include hyperirritability, cholinergic symptoms (e.g., diarrhea, sneezing), tachypnea, and termors.
Opioids cause constipation by binding to opioid receptors in the gastrointestinal tract resulting in decreased bowel motility through direct and indirect (anticholinergic) mechanisms. Withdrawal from the effects of the opioids leads to the elevation of acetylcholine levels, which causes cholinergic effects (e.g., diarrhea, sneezing) in neonates with neonatal abstinence syndrome.
A lack of opioids leads to decreased dopamine release, decreased serotonin release, and increased norepinephrine release. These changes in neurotransmitters result in hyperirritability. It is hypothesized that decreased dopamine plays a major role in the development of hyperirritability in patients with neonatal abstinence syndrome.
Neonatal abstinence syndrome is associated with increased acetylcholine levels, which leads to cholinergic symptoms such as sneezing.
Tremor is a common manifestation of neonatal abstinence syndrome and is likely related to changes in the neurotransmitter levels (e.g., increased norepinephrine, acetylcholine).
The Moro reflex is an infantile reflex characterized by involuntary abduction of the arms followed by involuntary adduction of the arms and crying in response to a rapid lowering of the infant. An exaggerated Moro reflex is characterized by a hyperactive response with excessive abduction at the shoulder and extension at the elbow. Neurotransmitter changes likely contribute to this.
Cholinergic symptoms (e.g., congestion), irritability, crying, and withdrawal from opioids (which normally decrease respiratory rate) lead to tachypnea, which is defined by abnormally increased breathing.
Maternal screening for substance use and early screening of newborns who are at risk is the key to the prevention and effective management of this condition.
Nonpharmacologic therapy is mainly targeted at alleviating symptoms and preventing complications. Gentle vertical rocking and caring in a quiet room is used for neonates with hyperirritability. Positioning and swaddling can be used to prevent motor hyperactivity in neonates with tremors.
Opioids can be used for the treatment of neonatal abstinence syndrome if symptoms are severe (e.g., severe irritability, severe diarrhea). Oral morphine sulfate is the preferred medication.
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