Hypoxic Ischaemic Encephalopathy

Question 1

Define

Answer 1

Acute brain dysfunction following critical lack of cerebral blood flow and oxygen delivery

Question 2

Causes

Answer 2

Causes of HIE:

In perinatal asphyxia, gas exchange (either placental or pulmonary) is compromised, leading to cardiorespiratory depression. This leads to hypoxia, hypercapnia and metabolic acidosis.

Reduced/ compromised cardiac output results in diminished tissue perfusion, which can lead to hypoxic ischaemic injury to the brain and other organs.

It is an important cause of brain damage, resulting in disability or death

Most cases occur following a significant event immediately before OR during labour/ delivery, such as:

Failure of gas exchange across the placenta
1. Excessive or prolonged uterine contractions
2. Placental abruption
3. Ruptured uterus

Interruption of umbilical blood flow (often from cord compression)
1. Cord prolapse
2. Shoulder dystocia

Inadequate maternal placental perfusion,
1. maternal hypo/hypertension

Compromised foetus
1. IUGR
2. Anaemia
3. Failure of cardiorespiratory adaptation at birth (failure to breathe)

Question 3

Clinical presentation

Answer 3

Clinical manifestations start IMMEDIATELY or up to 48 hours AFTER asphyxia and can be graded:

MILD
* Infant is irritable
* Responds excessively to stimulation
* May have staring of the eyes
* Hyperventilation, hypertonia
* Impaired feeding
* Complete recovery can be expected

MODERATE
* Infant shows marked abnormalities of movement
* Hypotonic
* Cannot feed
* May have seizures
* If fully resolved by 2 weeks of age, there is a good long-term prognosis
* If persistent past 2 weeks, bad prognosis

SEVERE
* There are NO normal spontaneous movements or response to pain.
* Tone in the limbs may fluctuate between hypotonia and hypertonia.
* Seizures are prolonged and often refractory to treatment.
* Multi-organ failure is present
* 30-40% mortality
* Over 80% have neurodisability (if not cooled) -> cerebral palsy

The neuronal damage from HIE may be immediate from primary neuronal death OR may be delayed from reperfusion injury causing secondary neuronal death.

NOTE: the delay offers the opportunity for neuroprotection with mild therapeutic hypothermia

Question 4

Investigations

Answer 4

Examination

Basic observations

Blood gases

Amplitude-integrated electroencephalogram (aEEG, cerebral function monitor) may be used to detect abnormal background brain activity to CONFIRM early encephalopathy (also used to identify seizures)

Doppler USS

Question 5

Management

Answer 5

Admit to NICU

Skilled resuscitation and stabilisation will minimise neuronal damage:

Respiratory support- ventilator or CPAP

Clinical seizures- treat with anticonvulsants

Fluid restriction because of transient renal impairment

Hypotension- treat by volume and inotrope support

Monitoring and treatment of hypoglycaemia and electrolyte imbalance, especially hypocalcaemia

MILD cooling
* Started WITHIN 6 HOURS of BIRTH (to a rectal temperature of 33-34oC for 72 hours)
* Wrapping infant in a cooling blanket
* Done in infants ≥ 36 weeks gestation with moderate or severe HIE
* Helps REDUCE brain damage
* Following cooling rewarming should be carried out slowly (0.5°C every 1 to 2 hours) over a period of 6-12 hours. 

Criteria for the use of therapeutic cooling in neonates: 
* Neonates with a gestational age ≥36 weeks and birth weight >1800g 
* History of acute perinatal event during delivery associated with period of hypoxia, and/or an Apgar score ≤5 at 10 minutes or at least 10 minutes of
positive-pressure ventilation
* Severe metabolic acidosis on cord gas, or blood gas taken within 1hr of birth 
* Evidence of moderate-severe HIE – demonstrated by onset of seizures, and/or on the basis of clinical assessment of consciousness level, spontaneous activity, posture, tone, primitive reflexes, and autonomic systems.

AVOID hyperthermia (> 37.5 oC)

Question 6

Complications

Answer 6

Complications

• Neurological damage- neurodevelopmental disabilities (particularly cerebral palsy)
• Death

Prognosis
* With mild HIE, a full recovery can be made
* Infants with moderate HIE who have recovered fully on neurological examination and are feeding NORMALLY by 2 weeks of age have a good long-term prognosis
* But if clinical abnormalities persist beyond this time, full recovery is unlikely
* Severe HIE has a mortality of 30-40%

If MRI shows significant abnormalities at 5-14 days, there is a very high risk of later cerebral palsy.

Encephalopathy may sometimes be caused by another neonatal condition e.g. inborn error of metabolism of kernicterus.

It has been recommended that infants who have clinical features of HIE should ONLY be considered to have birth asphyxia if there is:
* Evidence of severe hypoxia antenatally or during labour/ delivery
* Resuscitation needed at birth
* Features of encephalopathy
* Evidence of hypoxic damage to other organs e.g. liver, kidney or heart
* No other prenatal or postnatal cause identified