Hypoxic-Ischaemic Encephalopathy

Question 1

What is hypoxic-ischaemic encephalopathy (HIE)?

Answer 1

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 brain and encephalopathy refers to malfunctioning of the brain. Some hypoxia is normal during birth, however prolonged or severe hypoxia leads to ischaemic brain damage. HIE can lead to permanent damage to the brain, causing cerebral palsy. Severe HIE can result in death.

Question 2

When should HIE be suspected?

Answer 2

Suspected HIE in neonates when there are events that could lead to hypoxia during the perinatal or intrapartum period, acidosis (pH < 7) on the umbilical artery blood gas, poor Apgar scores, features of mild, moderate or severe HIE (see below) or evidence of multi organ failure.

Question 3

What causes HIE?

Answer 3

Anything that leads to asphyxia (deprivation of oxygen) to 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

Question 4

What grading system is used to assess HIE?

Answer 4

Sarnat Staging.

Question 5

Briefly differentiate between mild, moderate and severe HIE

Note: Sarnat Staging

Answer 5

Mild

• Poor feeding, generally irritability and hyper-alert
• Resolves within 24 hours
• Normal prognosis

Moderate

• Poor feeding, lethargic, hypotonic and seizures
• Can take weeks to resolve
• Up to 40% develop cerebral palsy

Severe

• Reduced consciousness, apnoeas, flaccid and reduced or absent reflexes
• Up to 50% mortality
• Up to 90% develop cerebral palsy

Question 6

How is HIE diagnosed?

Answer 6

Investigation of HIE is with EEG monitoring.

Question 7

Briefly describe the management of HIE

Answer 7

Management will be coordinated by specialists in neonatology, on the neonatal unit. This involves supportive care with neonatal resuscitation and ongoing optimal ventilation, circulatory support, nutrition, acid base balance and treatment of seizures. Therapeutic hypothermia is an option in certain circumstances to help protect the brain from hypoxic injury.

Children will need to be followed up by a paediatrician and the multidisciplinary team to assess their development and support any lasting disability.

Question 8

Briefly describe the role of therapeutic hypothermia in HIE

Answer 8

Babies near or at term considered to have HIE can benefit from therapeutic hypothermia. Therapeutic hypothermia involves actively cooling the core temperature of the baby according to a strict protocol. The baby is transferred to neonatal ICU and actively cooled using cooling blankets and a cooling hat. The temperature is carefully monitored with a target of between 33 and 34°C, measured using a rectal probe. This is continued for 72 hours, after which the baby is gradually warmed to a normal temperature over 6 hours.

The intention of therapeutic hypothermia is to reduce the inflammation and neurone loss after the acute hypoxic injury. It reduces the risk of cerebral palsy, developmental delay, learning disability, blindness and death.

Question 9

Briefly describe the prognosis of HIE

Answer 9

The prognosis of HIE depends on the degree of neurological damage. Severe cases are strongly associated with chronic neurological disability (especially cerebral palsy) and HIE is fatal in approximately 1/3 of severe cases. The degree of damage can be assessed with MRI.