Hypoxic ischaemic encephalopathy (HIE) occurs in neonates as a result of hypoxia during birth. Hypoxia is a lack of oxygen. Ischaemia refers to a restriction in blood flow to the tissues. Encephalopathy refers to the malfunctioning of the brain. Some hypoxia is normal during birth. However, prolonged or severe hypoxia leads to ischaemic brain injury. HIE may result in permanent neurological impairments, including cerebral palsy, developmental delays, cognitive deficits, or, in severe cases, death.
Causes of HIE
Anything that leads to asphyxia (deprivation of oxygen) in the brain can cause HIE. For example:
- Maternal shock
- Intrapartum haemorrhage
- Prolapsed cord, causing compression of the cord during birth
- Nuchal cord, where the cord is wrapped around the neck of the baby
Diagnosis
Factors that suggest possible HIE include:
- Hypoxia during the perinatal or intrapartum period
- Acidosis (pH <7.0 or base deficit ≥ 12-16 mmol/L) on the umbilical artery blood gas
- Poor Apgar scores (e.g., less than 5 at 10 minutes)
- Features of HIE (see below)
MRI and electroencephalography (EEG) may be used to help establish the diagnosis.
Sarnat Staging System
Mild HIE (grade 1):
- Hyperalertness
- Normal tone
- Intact reflexes
- Normally resolves within 24 hours with no lasting impairments
Moderate HIE (grade II):
- Lethargy
- Hypotonia
- Suppressed reflexes
- Possible seizures
- 20-50% develop cerebral palsy or developmental delay
Severe HIE (grade III):
- Flaccid tone
- Absent reflexes
- Frequent seizures
- High mortality (up to 50%)
- Up to 90% develop cerebral palsy or other disability
Management
Specialist management will take place in the neonatal intensive care unit. Supportive care involves neonatal resuscitation and ongoing optimal ventilation, circulatory support, nutrition, acid-base balance and treatment of seizures. Therapeutic hypothermia is used to help protect the brain from hypoxic injury.
They require follow-up to assess their development and support any lasting disability.
Therapeutic Hypothermia
Therapeutic hypothermia is used in term or near-term newborns with possible HIE (e.g., evidence of perinatal hypoxia or pH < 7.0). It reduces inflammation and neurone loss after the acute hypoxic injury. It reduces the risk of cerebral palsy, developmental delay, learning disability, blindness and death.
Therapeutic hypothermia involves actively cooling the core temperature according to a strict protocol using specialist cooling mattresses or blankets. The temperature is carefully monitored with a target between 33-34°C, measured using a rectal probe. Cooling is continued for 72 hours, followed by gradual warming over 6-12 hours.
Last updated May 2025
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