Pathophysiology
Clinical meaning
Neonatal Abstinence Syndrome (NAS), also called Neonatal Opioid Withdrawal Syndrome (NOWS), is a constellation of withdrawal signs and symptoms that occur in newborns who were exposed to opioids or other addictive substances during intrauterine development. When a pregnant person uses opioids (prescription or illicit), these lipophilic substances readily cross the placenta and blood-brain barrier, binding to mu-opioid receptors in the fetal central nervous system. The fetus develops physical dependence on the continuous opioid exposure, and after birth, when the drug supply is abruptly discontinued via separation from the placenta, the neonate experiences withdrawal. The pathophysiology of opioid withdrawal involves a sudden increase in norepinephrine release from the locus coeruleus, a brainstem nucleus that is normally inhibited by opioids. When opioid stimulation is removed, the locus coeruleus becomes hyperactive, flooding the central and autonomic nervous systems with norepinephrine. This catecholamine surge produces the characteristic signs of NAS: autonomic instability (temperature dysregulation, sweating, yawning, sneezing, nasal stuffiness), central nervous system excitability (high-pitched cry, tremors, increased muscle tone, seizures), gastrointestinal dysfunction (poor feeding, uncoordinated suck, vomiting, diarrhea, excessive weight loss), and metabolic stress...