Hypoxic-ischaemic encephalopathy, or HIE

By Dr Rosemary Listing, PhD (Product Liability), Of Counsel, Peter Evans & Associates | Birth trauma and obstetric negligence | Reading time: about 14 minutes

Few words are as frightening for new parents as "your baby may have a brain injury from lack of oxygen." The medical term is hypoxic-ischaemic encephalopathy, or HIE. It is also spelled hypoxic-ischemic encephalopathy, and is sometimes described as birth asphyxia or oxygen deprivation at birth. Within hours, parents are usually told their baby has mild, moderate or severe HIE, and that decision shapes everything that follows, including whether the baby receives cooling therapy.

This guide explains what each grade means, how doctors decide the grade, who qualifies for cooling, what outcomes look like for each grade, and when HIE may be linked to medical negligence in NSW. It focuses on grading, treatment and what happens after birth. For the causes of HIE during pregnancy and labour, read our companion guide, understanding HIE in newborns: a guide for parents considering legal action.

Key points

HIE is a brain injury caused by too little oxygen or blood flow to a baby's brain, usually around the time of birth. It affects roughly 1.5 in every 1,000 live births.
Doctors grade HIE as mild, moderate or severe (Sarnat stage 1, 2 or 3) by examining the baby's alertness, tone, reflexes and breathing, and watching for seizures.
Cooling therapy (therapeutic hypothermia) is standard care for moderate and severe HIE, but it must start within 6 hours of birth.
Mild HIE is not always harmless. A systematic review found about 1 in 4 babies with mild HIE had an abnormal outcome.
Negligence can occur before birth (how labour was managed) and after it (delays in recognising HIE, starting cooling or arranging transfer).

What is hypoxic-ischaemic encephalopathy (HIE)?

"Hypoxic" means not enough oxygen. "Ischaemic" means not enough blood flow. "Encephalopathy" means the brain is not working normally. The NSW Agency for Clinical Innovation (ACI) describes HIE as a form of neonatal encephalopathy caused by low oxygen in the blood and/or reduced blood flow to the brain from an acute event around birth. See its clinical practice guide on HIE in newborns (2024).

The brain injury does not all happen at once. There is an initial injury during the oxygen deprivation, then a "secondary" wave of injury in the hours and days afterwards. That second wave is why time matters so much. Cooling therapy works by slowing it down. Lack of oxygen can also affect other organs, including the heart, lungs, liver and kidneys.

A UK-based epidemiological review estimated the incidence of HIE at about 1.5 per 1,000 live births. Sydney's Royal Hospital for Women guideline gives a range of 1 to 3 per 1,000 for moderate to severe HIE in high-income countries.

Mild vs moderate vs severe HIE: what the grades mean

Doctors grade HIE using a neurological examination based on the Sarnat staging system, first described in the 1970s and now usually used in a modified form. You may hear the grades called "Sarnat stage 1, 2 and 3" or "HIE grade 1, 2 and 3". The table below gives a simplified, plain-language overview. It is not a diagnostic tool.

Feature	Mild HIE (stage 1)	Moderate HIE (stage 2)	Severe HIE (stage 3)
Alertness	Hyper-alert, jittery, irritable, wide-eyed	Lethargic, slow to respond	Stupor or coma, little or no response
Muscle tone	Normal or slightly increased	Floppy (reduced tone)	Very floppy (flaccid)
Posture	Mild flexion	Strong flexion of arms and legs	Abnormal posturing
Suck and reflexes	Weak suck; exaggerated startle (Moro) reflex	Weak suck; incomplete reflexes	Absent suck and reflexes
Breathing and autonomic signs	Generally normal breathing; dilated pupils, fast heart rate	Constricted pupils, slow heart rate, periodic breathing	Unequal or unreactive pupils, apnoea (pauses in breathing), unstable heart rate
Seizures	Uncommon	Common	Common; may be difficult to control
Cooling	Not usually offered; discuss with a neonatologist	Standard treatment if criteria met	Standard treatment if criteria met

Grading is not always fixed at the first examination. A baby's condition can change over the first hours, which is why guidelines require repeated assessments. A baby who looks "mild" at one hour may meet the criteria for moderate HIE at three hours.

How do doctors decide the grade?

In NSW, the ACI guide recommends the Newborn Encephalopathy Assessment Tool, a modified Sarnat assessment, for at-risk babies. It is performed hourly from 1 to 6 hours after birth. Each feature is scored as normal, mild, moderate or severe. The assessment should wait until the baby is stable, because encephalopathy cannot be reliably judged during active resuscitation.

Babies "at risk" include those who:

were born after signs of fetal distress, such as an abnormal CTG
needed significant resuscitation at birth
had a low Apgar score
had acidic cord or newborn blood gases (a low pH or a large base deficit)

Doctors may also use amplitude-integrated EEG (aEEG), a simplified brain-wave monitor, to support the grading and detect seizures. Many seizures in newborns have no visible signs.

Why the cord blood gas matters. The cord blood gas taken at birth is one of the most important pieces of evidence about whether a baby suffered oxygen deprivation around the time of birth. It also helps decide eligibility for cooling. If cord gases were not taken, or the samples were lost, that gap can matter later, both clinically and legally.

Cooling therapy for HIE: who qualifies?

Therapeutic hypothermia, or "cooling", lowers the baby's body temperature to around 33 to 34 °C for 72 hours, then rewarms the baby slowly. It is now the standard of care for moderate and severe HIE in babies born at or after 35 weeks. A Cochrane review of 11 trials (Jacobs et al, 2013) found cooling reduced the combined risk of death or major disability by 25%. About seven babies need to be cooled to prevent one death or major disability.

The NSW eligibility criteria

Under the ACI guide, a baby should be considered for cooling if all three of the following apply:

Age and size: born at 35 weeks or later, weighing at least 1,800 g, and less than 6 hours old.
Evidence of oxygen deprivation at birth, any one of:
- a cord or newborn blood gas in the first hour with pH below 7.00 or base excess of −12 mmol/L or worse
- an Apgar score below 6 at 10 minutes
- resuscitation (breathing support or chest compressions) for 10 minutes or more
Moderate or severe encephalopathy, any one of:
- three or more moderate or severe features between 1 and 6 hours
- two features plus an abnormal aEEG
- seizures

Cooling must not start without discussion with a tertiary neonatologist and the NSW Newborn and paediatric Emergency Transport Service (NETS). All cooled babies are transferred to a neonatal intensive care unit. The ACI's parent information sheet on cooling explains what families can expect, including gel packs or a cooling blanket, limited cuddling, and expressing breast milk while the baby cannot feed.

Why the 6-hour window is critical

Cooling works best when started early, ideally well within the first 6 hours. Babies born in regional or private hospitals without a NICU may need passive cooling (turning off heat sources) while waiting for the transport team. That process needs careful supervision. Safer Care Victoria's guideline on starting cooling in special care nurseries warns that overcooling below 32 °C has been linked to significant harm. It also warns that overheating is dangerous: the odds of death or disability rise up to four-fold for each degree above 37.5 °C. Victoria's equivalent of NETS is PIPER, which publishes its own cooling protocol.

When a baby who met the criteria is not identified, not referred, or not cooled in time, families lose the benefit of the one treatment proven to reduce brain injury.

MRI, EEG and other tests: what they show

MRI. Usually performed around day 4 to 10 of life, after cooling and rewarming. Queensland's clinical guideline on HIE recommends MRI at about day 7. An MRI done in the first 24 hours can falsely appear normal.
The pattern of injury matters. The Royal Hospital for Women's HIE guideline explains two main patterns. An acute, profound event (for example a cord prolapse or uterine rupture) tends to injure the basal ganglia and thalami, deep structures that control movement. A prolonged, partial lack of oxygen (for example over hours of labour) tends to injure the "watershed" areas of the brain.
EEG. A brain-wave background that returns to normal within about 48 hours is a good sign. A persistently abnormal background is associated with a higher risk of poor outcome.

These findings matter medically and legally. The MRI pattern, the cord gases and the CTG trace are often the key evidence about when the injury happened, and therefore whether better care in labour could have prevented it.

Was your baby diagnosed with HIE?

Dr Rosemary Listing can help you understand the grade, the treatment your baby received, and whether the care before and after birth met the required standard.

Book your free clarity call

Or call Peter Evans & Associates on 02 4926 4788

What are the outcomes for each grade?

Every baby is different, and early predictions can be wrong in both directions. General patterns from the research:

Grade	What the evidence suggests
Mild HIE	Many babies recover well, but it is not benign. A 2018 systematic review (Conway et al) found about 25% had an abnormal outcome at 18 months or older, including cerebral palsy or below-average developmental scores. Mild cases make up around half of all HIE.
Moderate HIE	Cooling has substantially improved outcomes. Many cooled babies survive without major disability, but a significant proportion have motor, learning, speech, vision, hearing or behavioural difficulties. These may not be apparent until the child is older.
Severe HIE	The highest risk of death and serious disability, including cerebral palsy (often spastic quadriplegia or dyskinetic types), epilepsy, intellectual disability, feeding difficulties and cortical visual impairment. Some families face decisions about redirecting care.

Overall, the Royal Hospital for Women's guideline notes that babies with moderate to severe HIE remain at a 30 to 70% risk of death or disability even with cooling. In the pooled Cochrane trials, death or major disability at 18 months fell from 61% without cooling to 46% with it.

The Queensland guideline recommends that all babies with HIE, including mild cases, be referred for neurodevelopmental follow-up. Cooled babies should be followed for at least two years, ideally until school age. If your child was not referred, ask for it.

"They said it was only mild." Is mild HIE really mild?

This is one of the most common questions parents ask, often years later when a child is diagnosed with learning, attention, coordination or speech difficulties. The honest answer is that "mild" describes how the baby looked in the first hours of life. It does not guarantee a mild long-term outcome.

Mild HIE matters for three reasons:

The grade can change. A baby graded mild at one hour may become moderate. If assessments were not repeated hourly as guidelines require, a baby who should have been cooled may have been missed.
Cooling for mild HIE is uncertain. Queensland's guideline says suitability should be discussed with a neonatologist. The evidence is still developing.
Problems may appear late. Difficulties may not be identified until preschool or school. This affects when a claim becomes "discoverable" under limitation law.

When is HIE caused or worsened by medical negligence?

Not every case of HIE is preventable. Some injuries occur before labour, and some have genetic, infective or metabolic causes. Defendants commonly argue that the injury happened before the hospital could have intervened. Separating preventable from unpreventable injury requires careful analysis of the CTG, cord gases, placental pathology and MRI pattern by independent experts.

Potential failures fall into two broad periods.

Before and during birth

These include failure to act on an abnormal CTG, delays in calling for help or moving to a caesarean, mismanagement of oxytocin, failure to respond to reduced foetal movements, and prolonged or difficult forceps or vacuum births. Delay in performing an emergency caesarean is a common thread, as discussed in our guide to caesarean safety and your legal rights. Our existing HIE causes guide covers these in detail.

After birth: the grading and cooling period

This period is often overlooked, but it can be decisive. Questions we examine include:

Was resuscitation at birth timely and effective, with senior staff called promptly?
Were cord gases taken and correctly interpreted?
Were encephalopathy assessments done hourly from 1 to 6 hours and documented?
Was a baby with evolving signs wrongly classed as mild, or not assessed at all?
Was NETS contacted promptly, and was cooling started within 6 hours?
Was passive cooling properly supervised, avoiding both overcooling and overheating?
Were seizures recognised and treated, with EEG monitoring?
Were low blood sugar and other complications managed?
Was the baby referred for MRI and long-term follow-up?

If you felt your concerns were brushed aside in the hours after birth, our article on when being dismissed by a doctor becomes a legal issue may help. Equipment problems, such as a faulty fetal monitor, are covered in birth injuries and medical devices.

HIE claims for children in NSW: what parents need to know

The standard of care

Claims are governed by the Civil Liability Act 2002 (NSW). Under section 5O, a health professional is not liable if they acted in a way widely accepted in Australia by peer professional opinion as competent practice, unless that opinion is irrational. Expert evidence from obstetricians, midwives, neonatologists, paediatric neurologists and neuroradiologists is central to HIE cases.

Time limits for children

The general rule under section 50C of the Limitation Act 1969 (NSW) is three years from discoverability, with a 12-year long-stop. Special rules apply to children, and in some situations time can run based on what a parent or guardian knew or ought to have known. Do not assume you can wait until your child turns 18. The NSW Judicial Commission's bench book on limitations explains the framework. Read our guides to NSW medical negligence time limits and whether you can still sue years later.

What a claim can cover

For a child with significant HIE, compensation may need to fund a lifetime of needs: medical and therapy costs, equipment, home and vehicle modifications, paid care, care provided by family, loss of future earning capacity, and management of the funds. The interaction between compensation and the NDIS needs specialist advice. Many families face financial strain while caring for a child with complex needs. We discuss this in medical negligence and financial debt in NSW.

Parents' own injuries

Parents who witness a traumatic birth and its aftermath can suffer recognised psychiatric injuries, such as post-traumatic stress disorder. In some circumstances, they may have their own claim. See maternal birth injuries: what we must talk about.

What to do now

Ask for an open disclosure meeting under the Australian Open Disclosure Framework. Ask what grade your baby was given, when, and on what findings.
Request complete records for both mother and baby. These include the CTG, partogram, cord gases, resuscitation record, neonatal encephalopathy assessments, NETS records, cooling charts, EEG, MRI reports and images, and placental pathology.
Keep every follow-up appointment and keep copies of developmental assessments.
Raise concerns with the NSW Health Care Complaints Commission if appropriate. A complaint does not replace a compensation claim.
Get legal advice early. Evidence such as CTG traces and MRI images must be preserved.

How we can help

Dr Rosemary Listing acts only for injured patients and families. She focuses on birth trauma and obstetric negligence. Her method maps every decision point across labour, birth and the first hours of life. It does not stop at the delivery room door, because in HIE cases the first six hours after birth can be as important as labour itself. She also trains maternity clinicians through birth trauma training with the Maternity Consumer Network.

Learn more about Dr Listing, explore the resource hub, or read Ms Jones' story of justice and healing after birth trauma. If a family member suffered oxygen deprivation during an operation rather than at birth, see brain injury from hypoxia during surgery.

You deserve to understand what happened to your baby.

Your first conversation is free and confidential. You do not need your records to start.

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Frequently asked questions about HIE grades

What is the difference between mild, moderate and severe HIE?

The grade reflects how affected the baby's brain function is in the first hours after birth. Babies with mild HIE are usually jittery or hyper-alert. Babies with moderate HIE are lethargic and floppy and often have seizures. Babies with severe HIE are unresponsive or in a coma, with absent reflexes and breathing problems.

Is HIE the same as cerebral palsy?

No. HIE is the brain injury diagnosed around birth. Cerebral palsy is a lifelong movement disorder that some children develop as a result of brain injury, including HIE. Not every child with HIE develops cerebral palsy, and not all cerebral palsy is caused by oxygen deprivation at birth.

Why wasn't my baby cooled?

In NSW, cooling is offered to babies born at 35 weeks or later, within 6 hours of birth, who show evidence of oxygen deprivation and have moderate or severe encephalopathy. Babies with mild HIE are not usually cooled. If your baby met the criteria but was not cooled, or was assessed too late, ask for an explanation and seek advice.

Can mild HIE cause long-term problems?

Yes. Research suggests about one in four babies with mild HIE have an abnormal developmental outcome. Queensland's clinical guideline recommends neurodevelopmental follow-up for all babies with HIE, including mild cases.

How long does cooling last?

Cooling usually lasts 72 hours at around 33 to 34 °C, followed by slow rewarming over several hours. Babies are cared for in a neonatal intensive care unit throughout.

Can I make a claim if my baby has HIE?

You may have a claim if the HIE, or its severity, was caused by care that fell below the accepted standard. This can include care in labour or delays in recognition and cooling after birth. Special time limit rules apply to children, so it is important to get advice early.

Sources

NSW Agency for Clinical Innovation, Hypoxic ischaemic encephalopathy in newborns: recognition, monitoring and early management (2024) and parent information sheet
Royal Hospital for Women (SESLHD), HIE in infants ≥35 weeks gestation (CLIN070) (2024)
Queensland Clinical Guidelines, Hypoxic ischaemic encephalopathy guideline supplement
Safer Care Victoria, Commencement of therapeutic hypothermia in a special care nursery
PIPER (Royal Children's Hospital Melbourne), Therapeutic hypothermia for HIE
Jacobs SE et al, Cooling for newborns with hypoxic ischaemic encephalopathy, Cochrane Database of Systematic Reviews 2013
Conway JM et al, Mild hypoxic ischaemic encephalopathy and long term neurodevelopmental outcome: a systematic review, Early Human Development 2018
Epidemiology of neonatal encephalopathy and hypoxic-ischaemic encephalopathy, Early Human Development 2010

This article provides general information only. It is not medical or legal advice and should not be relied on as a substitute for advice about your circumstances. Reframe Legal is a thought leadership website by Dr Rosemary Listing. Legal services are provided by Peter Evans & Associates. Liability limited by a scheme approved under Professional Standards Legislation.