Hypoxic Ischaemic Encephalopathy
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Direct answer
Hypoxic ischaemic encephalopathy is a neurological syndrome of the term newborn caused by perinatal asphyxia, in which reduced oxygen and blood flow injure the brain and often other organs. It is graded by Sarnat staging into mild, moderate and severe disease, and the stage predicts the outcome. Management is supportive, with resuscitation, careful monitoring and therapeutic hypothermia for eligible moderate or severe cases.
What you must remember
- Definition: an encephalopathy following an acute perinatal insult, with neurological signs and, typically, injury to other organs.
- Asphyxia markers: an Apgar score of 0 to 3 beyond five minutes, cord arterial pH below 7.0 or base deficit of 12 or more, and an acute event around delivery.
- Sarnat stage I: hyperalert, hyperreflexic and mostly resolving within about 24 hours, with a good outlook.
- Sarnat stage II: lethargic, hypotonic, often with seizures and an abnormal EEG, lasting up to about two weeks.
- Sarnat stage III: stuporous or comatose, flaccid with absent reflexes, carrying the highest risk of death or severe disability.
- Multi-organ injury: acute kidney injury, transaminase rise, myocardial dysfunction, persistent pulmonary hypertension, necrotising enterocolitis and coagulopathy.
- MRI: injury to the basal ganglia and thalami is the pattern most strongly linked with poor outcome, and the first week is the most useful time to image.
Sarnat staging and what it predicts
Sarnat staging is the bedside tool examiners expect, because it grades encephalopathy by consciousness, tone, reflexes and seizures. The table sets out the three stages, and the stage seen in the first 24 hours is the most useful guide to prognosis.
| Feature | Stage I, mild | Stage II, moderate | Stage III, severe |
|---|---|---|---|
| Consciousness | Hyperalert | Lethargic | Stupor or coma |
| Muscle tone | Normal | Hypotonic | Flaccid |
| Reflexes | Hyperreflexic | Hyperreflexic | Depressed or absent |
| Usual course | Within about 24 hours | Up to about two weeks | Days, with poor outlook |
Seizures and EEG findings add to the picture, with seizures typical of stage II and the EEG most abnormal in stage III. Because the stage can change from hour to hour, it is recorded serially rather than once.
A baby with moderate disease may improve towards mild stage over the first days, which is why repeated examinations tell the examiner more than a single one. The stage in the early hours also decides whether the baby is eligible for therapeutic cooling.
Where the exam tries to catch you
Hypoxic ischaemic encephalopathy stems usually test the diagnostic criteria, the Sarnat stage and the timing of imaging.
- Trap: calling every term baby with a low Apgar score hypoxic ischaemic encephalopathy. Correct: the Apgar score alone does not diagnose it, because the criteria also need an acute event and neurological and organ involvement.
- Trap: starting cooling for a mild stage I baby who is improving. Correct: therapeutic hypothermia is for moderate or severe encephalopathy, and mild cases usually recover without it.
- Trap: reading a normal early MRI as proof of no brain injury. Correct: early imaging is most informative in the first week, but injury can evolve, so follow-up remains necessary.
Frequently asked questions
What are the criteria for diagnosing hypoxic ischaemic encephalopathy?
Commonly used criteria for hypoxic ischaemic encephalopathy include an Apgar score of 0 to 3 beyond five minutes, cord arterial pH below 7.0 or base deficit of 12 or more, neurological signs, and involvement of other organs. An acute perinatal event must also be present.
What is the Sarnat stage in hypoxic ischaemic encephalopathy?
The Sarnat stage in hypoxic ischaemic encephalopathy grades the baby as mild, moderate or severe, based on consciousness, tone, reflexes and seizures. Stage III carries the highest risk of death or disability, while stage I usually recovers.
Which MRI pattern in hypoxic ischaemic encephalopathy predicts poor outcome?
Injury to the basal ganglia and thalami is the MRI pattern most strongly linked with poor neurodevelopmental outcome in term infants with hypoxic ischaemic encephalopathy. Imaging in the first week is the most useful timing for this assessment.
Which other organs are affected in hypoxic ischaemic encephalopathy?
Hypoxic ischaemic encephalopathy can affect the kidneys, liver, heart, lungs, gut and clotting system as well as the brain. Acute kidney injury, transaminase rise and pulmonary hypertension are common examples that need checking during management.