Intrapartum Asphyxia and Hypoxic-Ischaemic Encephalopathy
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Direct answer
Intrapartum asphyxia is a shortage of oxygen reaching the fetus during labour, and when it is severe it leads to hypoxic-ischaemic encephalopathy (HIE), a brain injury in the newborn. The firmest objective evidence is an umbilical arterial pH below 7.0 with a base deficit of 12 mmol/L or more. Moderate to severe HIE in a term infant is treated with whole-body cooling started within six hours of birth.
What you must remember
- Cord gas criteria: umbilical arterial pH below 7.0 and a base deficit of 12 mmol/L or more are the strongest objective markers of acute intrapartum hypoxia.
- Apgar score: a score of 0 to 3 persisting beyond five minutes supports the diagnosis but cannot establish asphyxia on its own.
- Sarnat staging: stage 1 is mild and usually resolves within a day, stage 2 is moderate with lethargy, hypotonia and seizures, and stage 3 is severe with stupor, flaccidity and a suppressed EEG.
- Therapeutic hypothermia: whole-body cooling to about 33.5°C for 72 hours, begun within six hours of birth, is indicated for moderate to severe HIE in term infants.
- Cerebral palsy link: intrapartum asphyxia explains only a minority of cerebral palsy, and antenatal causes account for most cases.
- Intrapartum surveillance: an abnormal cardiotocography tracing or a fetal scalp pH below 7.20 signals the need for prompt delivery.
- Long-term outcome: survivors may have cerebral palsy, epilepsy or cognitive impairment, and stage 3 carries a high risk of death.
A graded pathway from cord gas to cooling
Consider a term baby born limp after a prolonged labour with a bradycardic trace. The steps below show how the team confirms the injury, grades it and decides on cooling.
- Resuscitate at birth: support airway, breathing and circulation as per standard neonatal resuscitation, and check glucose and temperature early.
- Collect cord gas: sample umbilical arterial blood for pH and base deficit, because venous samples do not give a reliable picture of acidosis.
- Grade the encephalopathy: assess consciousness, tone, reflexes, seizures and feeding, then assign Sarnat stage 1, 2 or 3.
- Decide on cooling: start whole-body cooling for moderate or severe HIE within six hours of birth, aiming for a core temperature near 33.5°C.
- Maintain and rewarm: hold cooling for 72 hours, then rewarm gradually while watching for seizures, arrhythmia and coagulopathy.
- Plan follow-up: refer for neurodevelopmental review and early physiotherapy, since prognosis follows the stage and imaging findings.
Cooling is neuroprotective but does not reverse damage already done. Its benefit depends on an early start and the correct duration, so delay in referral to a neonatal intensive care centre costs the baby that benefit.
Where the exam tries to catch you
Vignettes tend to test a few predictable misconceptions about this condition.
- Trap: Diagnosing asphyxia from a low Apgar score alone. Correct: Apgar scores are nonspecific, so acidaemia on cord gas and neonatal neurological signs are needed to confirm the diagnosis.
- Trap: Assuming every encephalopathic baby will develop cerebral palsy. Correct: Stage 1 HIE often recovers fully, whereas stage 3 carries a high risk of death or severe disability.
- Trap: Starting cooling after the six-hour window. Correct: The neuroprotective benefit depends on early initiation, so eligible babies must be identified and referred quickly.
- Trap: Blaming labour for all cerebral palsy. Correct: Most cerebral palsy has antenatal origins, and intrapartum asphyxia is a minority contributor.
Frequently asked questions
Which cord blood values confirm intrapartum asphyxia?
Umbilical arterial pH below 7.0 with a base deficit of 12 mmol/L or more are the standard cord gas criteria for intrapartum asphyxia. These are read alongside Apgar scores beyond five minutes and early neurological signs in the newborn. No single value confirms the diagnosis by itself.
What does Sarnat staging classify in neonatal HIE?
Sarnat staging grades neonatal hypoxic-ischaemic encephalopathy as mild, moderate or severe, based on consciousness, muscle tone, reflexes and seizures. The stage predicts outcome and helps decide whether therapeutic hypothermia is indicated.
What is the time window for therapeutic hypothermia in HIE?
Therapeutic hypothermia for neonatal HIE must start within six hours of birth. It is usually continued for 72 hours and is reserved for term infants with moderate to severe encephalopathy. The benefit falls away when initiation is delayed.
Is intrapartum asphyxia the commonest cause of cerebral palsy?
No, intrapartum asphyxia causes only a minority of cerebral palsy cases. Antenatal factors such as malformations, infections and prenatal brain injury account for most cases.