Neonatal Encephalopathy vs HIE: Understanding the Terminology Doctors Use

Parents of a baby admitted to the NICU often see two terms used almost interchangeably in the chart and by different team members: neonatal encephalopathy and HIE. They mean related but meaningfully different things. Understanding the difference matters for cooling eligibility, for long-term prognosis, and for case review. This guide walks through what each term means, why doctors use both, how the severity is classified, and what each diagnosis does and doesn’t imply about cause.

What Is Neonatal Encephalopathy?

Neonatal encephalopathy (NE) is a clinical syndrome. It describes a newborn whose neurologic function is abnormal in the earliest days of life. The formal features include:

• Altered level of consciousness (hyperalert, lethargic, stuporous, or comatose).
• Abnormal muscle tone (either increased or decreased).
• Abnormal primitive reflexes (weak, absent, or exaggerated suck, Moro, grasp, or gag reflexes).
• Feeding or respiratory difficulties.
• Seizures, which are common in moderate-to-severe cases.
• Autonomic dysfunction such as unstable heart rate or blood pressure.

NE is an umbrella term. It describes what the baby looks like clinically, not why the baby looks that way. A diagnosis of NE tells clinicians the baby needs careful neurologic support and evaluation. It does not, by itself, tell them the cause.

What Is HIE?

Hypoxic-ischemic encephalopathy (HIE) is a specific subset of neonatal encephalopathy. It is NE caused by a hypoxic-ischemic event around the time of birth, where hypoxic means low oxygen and ischemic means reduced blood flow. Typical causes include:

• Placental abruption or acute placental insufficiency.
• Umbilical cord prolapse or severe cord compression.
• Uterine rupture.
• Prolonged or severe fetal distress that was not acted on.
• Severe maternal hypotension or cardiorespiratory arrest.

A diagnosis of HIE typically requires: (1) a clinical picture consistent with NE, (2) evidence of a peripartum oxygen-deprivation event (cord pH, Apgar scores, resuscitation record, or a documented sentinel event), and (3) imaging or EEG findings compatible with hypoxic-ischemic injury. The 2014 ACOG/AAP task force report provides detailed criteria for making this specific diagnosis.

The 2014 ACOG/AAP criteria for intrapartum HIE

The 2014 task force report set out specific criteria for attributing neonatal encephalopathy to an intrapartum hypoxic-ischemic event. All four of these neonatal signs are expected:

• Apgar score of less than 5 at 5 and 10 minutes.
• Fetal umbilical artery acidemia: pH below 7.0, or base deficit of 12 mmol/L or greater, or both.
• Brain imaging (MRI or MR spectroscopy) showing acute injury consistent with hypoxia-ischemia.
• Multi-system organ failure consistent with hypoxia-ischemia.

Additionally, the report identifies contributing factors that support an intrapartum cause, including a sentinel hypoxic or ischemic event immediately before or during labor, sudden sustained fetal bradycardia, a category III fetal heart rate tracing, and imaging patterns typical of peripartum injury rather than chronic or congenital disease. When these criteria are not met, the encephalopathy usually has a different cause.

Why the Terminology Matters

Before 2014, many clinicians used “HIE” as the default label for any encephalopathic newborn, even when the cause was unclear. This created two problems:

1. It implied birth asphyxia in cases where the cause was actually infection, metabolic disease, stroke, or a congenital condition.
2. It narrowed the diagnostic workup. Calling every encephalopathic baby “HIE” sometimes led to missed metabolic or infectious diagnoses that have different treatments.

The 2014 ACOG/AAP Neonatal Encephalopathy and Neurologic Outcome report, Second Edition formalized the preference for starting with the clinical term “neonatal encephalopathy” and specifying “HIE” only when a hypoxic-ischemic cause is established. The change aligns terminology with evidence and acknowledges that the majority of neonatal encephalopathy is not caused by intrapartum events.

How Doctors Use Both Terms Today

In practice, the two terms often appear in a baby’s chart in sequence. A typical NICU documentation pattern looks like this:

If you are reading your baby’s chart and the labels seem to shift across days, this is usually why. It does not necessarily indicate disagreement among the team; it reflects refining a diagnosis as more information becomes available.

Sarnat Staging: Mild, Moderate, and Severe

The severity of encephalopathy is classified using the Sarnat staging system, named after Sarnat and Sarnat’s original 1976 Archives of Neurology paper. The three stages describe a spectrum of clinical findings:

Sarnat staging matters for cooling eligibility. Therapeutic hypothermia is indicated for moderate-to-severe HIE (Sarnat stages 2 and 3) when other criteria are met. Mild HIE is generally not cooled, although this is an active area of ongoing research.

How Sarnat stage is determined

Sarnat stage is assigned by neurological examination, typically performed and repeated in the first hours of life by a neonatologist or pediatric neurologist. The exam covers six categories: level of consciousness, spontaneous activity, muscle tone, posture, primitive reflexes (suck, Moro), and autonomic function (heart rate, pupils, breathing). Each category is scored, and the overall stage reflects the most affected features. Because stage can change over the first hours, serial exams are standard. The stage documented closest to the 6-hour cooling window is usually the one that drives the decision to initiate hypothermia.

Supporting tools include amplitude-integrated EEG (aEEG), which provides continuous information on the brain’s background activity, and conventional EEG, which is the gold standard for detecting subclinical seizures. Both are often started within the first hours after birth in any baby with moderate or severe encephalopathy.

What Each Diagnosis Means for Your Baby

The implications of the specific diagnosis are practical, not just linguistic:

• Treatment differs by cause. HIE is treated with therapeutic hypothermia within 6 hours. Sepsis-related NE is treated with antibiotics. Metabolic disease may require specific dietary or medication management. Stroke requires different neurologic monitoring.
• Prognosis depends on severity, cause, and MRI findings. Brain MRI performed around day 4 to 7 after cooling (or after clinical stabilization) is the most useful prognostic test. The pattern of injury on MRI often predicts long-term outcome.
• Long-term follow-up is similar. Regardless of cause, babies with moderate-to-severe encephalopathy need neurodevelopmental follow-up through at least age 2, and earlier intervention for any identified delays.
• Case-review implications differ. If the cause was intrapartum hypoxic-ischemic injury that should have been detected, the review focuses on the fetal heart rate tracing and the delivery timeline. If the cause was sepsis, metabolic, or congenital, the review focuses on different aspects of prenatal or newborn care.

What to Look for in Your Baby’s Records

If you are trying to understand exactly what was diagnosed, these are the documents and findings to focus on:

• The neurological exam notes from the first 24 hours, which document Sarnat stage.
• Cord blood gas results (arterial and venous pH, base deficit, lactate).
• Apgar scores at 1, 5, and 10 minutes.
• The neonatal resuscitation record.
• The cooling eligibility assessment, including why cooling was or was not initiated.
• EEG or amplitude-integrated EEG reports.
• Brain MRI report, typically obtained after cooling completes.
• Metabolic and infectious workup results if another cause was considered.
• The placental pathology report, which often helps distinguish chronic from acute insults.
• The discharge summary’s final diagnosis.

Reading these together usually clarifies both the specific diagnosis and the reasoning behind it. If terms are being used loosely or inconsistently, a medical-record reviewer or pediatric neurologist can help you interpret them.

Quick Reference: NE vs HIE at a Glance

If you need a one-paragraph way to describe the distinction to family members or another clinician, this summary captures the essentials:

When reading your baby’s records, the key question is whether the encephalopathy was eventually attributed to a specific cause and whether that cause was an intrapartum event that should have been detected.

Related reading for parents

• Cord blood gas results explained: pH, base deficit, and what they mean for HIE
• Who qualifies for therapeutic cooling? HIE eligibility criteria explained
• The 6-hour window for HIE cooling: why timing is everything
• Placental insufficiency and HIE: when the placenta fails before delivery
• Chorioamnionitis and HIE: how infection in the womb causes newborn brain injury