HIE – Hypoxic-Ischemic Encephalopathy

image of a new born in nicu with tubs in mouth, and wires all over the bodyHIE injury is a significant cause of Cerebral Palsy.  HIE is a brain injury that is caused by lack of oxygen “asphyxia” (ie, hypoxia, acidosis).   HIE injuries in full term infants can be caused by a number of factors including placenta abruption or placenta previa.   Abruption occurs when the placenta seperates from the uterus and previa occurs when the placenta covers the cervix.   Both cause excessive bleeding during labor and delivery and cause the baby to suffer from lack of oxygen.   Other causes include a ruptured Uterus (where the wall of the Uterus tears), and twisting, knotting, compression or prolapsing of the unbilical cord.  Finally, in rare cases an Amniotic Fluid Embolism (ATE) can occur.  This a rare delivery complication where the amniotic fluid enters the mothers blood stream and causes colapse of the respiratory and cardiovascular systems.  The prognosis for mother and child are often catestrophic with HIE often effecting both mother and child.

HIE can also be caused by cardiac arrest, respiratory arrest, near-drowning, near-hanging, and other forms of incomplete suffocation, carbon monoxide and other poisonous gas exposures.

The WHO (World Health Organization) reports 23% of neonatal deaths worldwide are due to some form of birth related HIE.

HIE can occur at earlier points in the pregnancy.   Depennding on when HIE occurs the part of the brain injured is different.  This is becuase the developing brain requires more oxygen in areas of high metabolic activity, in different critical areas at differnet times.  When HIE injury occurs in a full term infant, the damage is typically to the upper brainstem, thalamus, cerebellum, basal ganglia, medial temporal structures (especially the CA1 field of the hippocampus), cortical layers 3, 5, and 6, as well as the cerebral hemispheric deep white matter.

In recent years, brain cooling and body cooling have proven to be effective mechanisms to stop the destructive effects of an HIE injury.   Damage to the brain cells occur at the time of the HIE event, but cell death continues for the next 48-72 hours.   Cooling has proven to slow down the metabolic activity of the brain cells and thus spares them from further damage.  Unfortunitly, the window of oppertunity for cooling is very short.  If the infant is not cooled in the first hours after birth, the technique will not help.

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