Hypoxic-Ischemic
Encephalopathy
and Other Neonatal
Encephalopathies

REVIEW ARTICLE


C O N T I N U UM A U D I O
I NT E R V I E W A V A I L AB L E
ONLINE

By Hannah C. Glass, MDCM, MAS

ABSTRACT
PURPOSE OF REVIEW: Neonatal encephalopathy is the most common condition
in neonates encountered by child neurologists. The etiology is most often
global hypoxia-ischemia due to failure of cerebral perfusion to the fetus
caused by uterine, placental, or umbilical cord compromise prior to or
during delivery. Other etiologies of neonatal encephalopathy include
ischemic stroke and intracranial hemorrhage, infection, developmental
anomalies, and inborn errors of metabolism.
RECENT FINDINGS: Therapeutic hypothermia is standard of care for the

treatment of neonatal encephalopathy presumed to be caused by
hypoxia-ischemia. The number needed to treat is approximately 6 to 7 to
prevent one child from either death or disability at age 18 to 22 months. EEG
monitoring and MRI are important tools in determining the etiology of
encephalopathy and prognosis of the infant.
SUMMARY: Neonatal encephalopathy is a heterogeneous disorder that is

characterized by alterations in mental status, hypotonia, seizures, and
abnormalities in feeding and respiration. The most common cause of
neonatal encephalopathy is hypoxic-ischemic encephalopathy, for which
treatment with 72 hours of therapeutic hypothermia is associated with
reduced death or disability.

INTRODUCTION
eonatal encephalopathy is a heterogeneous condition that can be due
to any disorder that disrupts the central nervous system in the first
days of life. The characteristic signs of neonatal encephalopathy are
altered mental status (eg, irritability, decreased responsiveness,
coma), seizures, hypotonia, abnormal primitive reflexes, apnea,
feeding disturbance, and abnormal cry.1 Neonatal encephalopathy may be
transient and reversible or may be the first sign of a brain injury, intracranial
infection, or brain malformation that leads to a lifelong disability.
Neonatal encephalopathy that is caused by an intrapartum event leading to
perinatal hypoxia-ischemia (sometimes called perinatal asphyxia) has historically
been called hypoxic-ischemic encephalopathy (HIE); however, some prefer the term

N

CITE AS:
CONTINUUM (MINNEAP MINN)
2018;24(1, CHILD NEUROLOGY):
57–71.

Address correspondence to
Dr Hannah C. Glass, 675 Nelson
Rising Ln, Box 0663, San
Francisco, CA 94158, Hannah.
Glass@ucsf.edu.
RELATIONSHIP DISCLOSURE:

Dr Glass has served on the
editorial board of Pediatric
Neurology and has given expert
medical testimony related to
medicolegal proceedings.
Dr Glass receives research/grant
support from the Cerebral Palsy
Alliance, National
Institutes of Health (grant
numbers 1P01NS082330,
1UG3OD023272, and
R03HD090298), Patient-Centered
Outcomes Research Institute,
and Pediatric Epilepsy
Research Foundation.
UNLABELED USE OF
PRODUCTS/INVESTIGATIONAL
USE DISCLOSURE:

Dr Glass discusses the
unlabeled/investigational use of
fosphenytoin, levetiracetam, and
phenobarbital for the treatment
of neonatal seizure disorders.
© 2018 American Academy
of Neurology.

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HYPOXIC-ISCHEMIC ENCEPHALOPATHY

neonatal encephalopathy given that the exact pathogenesis is often not known.2,3
In this article, the term neonatal encephalopathy will be used as an umbrella term
that encompasses HIE (or encephalopathy that is presumed to be caused by
hypoxia-ischemia).
EPIDEMIOLOGY
The incidence of neonatal encephalopathy in the developed world is estimated
at 2 to 6 per 1000 live term births, with HIE occurring in approximately 1.5 per
1000 live term births.4–6 Neonatal encephalopathy that is due to suspected or
confirmed HIE is among the most common diagnoses encountered by a child
neurologist and accounts for approximately 40% of new consults in the neonatal
intensive care unit.7,8
CLINICAL PRESENTATION
Clinical signs of encephalopathy include changes in consciousness and tone
and depressed primitive reflexes as well as seizures. Sarnat and colleagues9
classified the severity of encephalopathy in the setting of presumed HIE as
mild, moderate, or severe based on the worst degree of encephalopathy as
observed on serial examinations. Importantly, the severity of encephalopathy
is associated with mortality. Children with severe encephalopathy have a high
rate of mortality, and survivors have a very high likelihood of permanent
neurologic disability, whereas those with mild encephalopathy survive, and
those with moderate encephalopathy have intermediate rates of death
or disability.
ETIOLOGY
Neonatal encephalopathy may be due to a variety of conditions that can impair
the central nervous system. While a well-defined hypoxic-ischemic event (eg,
placental abruption, uterine rupture, cord prolapse) is the cause of encephalopathy
in many infants, other causes of altered mental status or seizures in a neonate
include ischemic or hemorrhagic stroke, infection, brain malformation, genetic
conditions, and inborn errors of metabolism (TABLE 3-1 10). Often, the exact
etiology remains unexplained.
In many neonates with encephalopathy, the initial encephalopathy and
seizures may resolve in the neonatal period. However, if the child has
experienced a brain injury, neurologic deficits can emerge as the child ages.
EVALUATION OF THE NEONATE WITH ENCEPHALOPATHY
Since the etiology of encephalopathy is broad, a careful evaluation is warranted,
especially in cases where the risk of perinatal asphyxia is low or where no sentinel
event occurred.
History and Physical Examination
Maternal history should focus on an evaluation for antecedents of neonatal
encephalopathy, including maternal medical history (eg, history of thromboembolic
disorders and pregnancy loss) and use of medications or substance abuse, obstetric
history (eg, results of prenatal screening and fetal ultrasounds), intrapartum events
(including fetal heart rate monitoring), and placental pathology (to evaluate for
placental abruption, vascular lesion, infection, or umbilical cord thrombosis). A
family history of epilepsy and congenital neurologic and neuromuscular conditions
may be a clue to a diagnosis other than HIE.

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The infant’s history must detail the onset, timing, and progression of
encephalopathy and seizures. The presence of oliguria, hypotension, transaminitis,
or coagulopathy suggests multiorgan failure and can support the occurrence of a
global hypoxic event and a diagnosis of HIE.
In addition to a comprehensive neurologic examination, neonates should be
carefully evaluated for signs of abnormal fetal development, including
dysmorphic craniofacial features, birthmarks, and congenital anomalies of the
internal organs and skeleton. A single or absent palmar crease, micrognathia, and
joint contractures can indicate a long-standing decrease in fetal movements,
suggesting prenatal onset of encephalopathy.
Laboratory Evaluation
Umbilical artery pH and base excess provide important clues regarding fetal
perfusion. A comprehensive laboratory evaluation also includes newborn blood
gas and lactate levels; a complete blood cell count, C-reactive protein, calcitonin,
and blood cultures to look for signs of infection; glucose; electrolyte panel; tests
for liver enzymes; creatinine and blood urea nitrogen; bilirubin levels; and a
coagulation profile. If central nervous system infection is suspected, lumbar
puncture should be performed for cell count, cultures, and viral studies (eg, herpes
simplex virus, Parechovirus, and rotavirus, among others). In areas without a
comprehensive newborn screen to test for inborn errors of metabolism or in cases
where an inborn error of metabolism is suspected, additional evaluation including
serum ammonia, serum amino acids, and urine organic acids may be warranted.
Genetic evaluation, including single-nucleotide polymorphism array, is
important to evaluate for the cause of congenital anomalies (including isolated
brain malformations) and suspected syndromic diagnoses.
Neurophysiologic Monitoring
According to the American Clinical Neurophysiology Society, neurophysiologic
brain monitoring using continuous video-EEG or, if continuous EEG is not
available, an adapted montage and trending such as amplitude-integrated EEG is
important to assess the degree of encephalopathy and recovery, as well as the
presence of seizures.11 Clinical evaluation alone without neuromonitoring can both
overestimate and underestimate the burden of seizures. Clinical observation
is unreliable, as movements that are not seizures may be interpreted as such
by the bedside staff.12,13 In addition, neonates frequently have seizures
without clinical correlate (subclinical seizures), and so seizures may go
undetected or underrecognized in neonates who do not receive monitoring.14–16
Amplitude-integrated EEG is a limited channel recording that is displayed as a
compressed tracing at the bedside (FIGURE 3-1).17 The advantage of this tool is
that it is easy to apply and interpret by bedside nursing and medical staff. The
primary disadvantage is that it has lower accuracy for seizure detection.
Neurophysiologic brain monitoring should continue for at least 24 hours or until
24 hours after the last seizure.11

KEY POINTS
● The hallmark signs of
neonatal encephalopathy
are altered mental status
(eg, irritability, lethargy,
coma), seizures, hypotonia,
abnormal primitive reflexes,
apnea, feeding disturbance,
and abnormal cry.
● Neonatal encephalopathy
that is caused by an
intrapartum event leading to
perinatal hypoxia-ischemia
(sometimes called perinatal
asphyxia) has historically
been called hypoxic-ischemic
encephalopathy; however,
some prefer the term
neonatal encephalopathy
given that the exact
pathogenesis is often
not known.
● While a well-defined
hypoxic-ischemic event (eg,
placental abruption, uterine
rupture, cord prolapse) is
the cause of
encephalopathy in many
infants, other causes of
altered mental status or
seizures in a neonate
include ischemic or
hemorrhagic stroke,
infection, brain
malformation, genetic
conditions, and inborn
errors of metabolism.
● In addition to a
comprehensive neurologic
examination, neonates with
encephalopathy should be
carefully evaluated for signs
of abnormal fetal
development, including
dysmorphic craniofacial
features, birthmarks, and
congenital anomalies of the
internal organs and skeleton.

Neuroimaging
MRI is recommended for all neonates with encephalopathy or seizures to assist
with identifying the etiology of encephalopathy and to assist with prognosis.
Head ultrasound is useful as a bedside tool to determine the presence of
hemorrhage or ventriculomegaly; however, after a hypoxic-ischemic event,

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HYPOXIC-ISCHEMIC ENCEPHALOPATHY

head ultrasound is often normal in the acute setting.18 CT is rarely used in
infants because of the need for high radiation doses to achieve adequate
resolution of brain parenchyma.
MRI can be performed safely (and often without sedation) in critically ill
children with appropriate monitoring and training. In addition to conventional
imaging (T1- and T2-weighted MRI), diffusion-weighted imaging (DWI) and
magnetic resonance spectroscopy are important to identify acute injury, whereas
susceptibility-weighted imaging (SWI) can improve identification of small areas

TABLE 3-1

Differential Diagnosis of a Neonate With Altered Mental Status or Seizures

Hypoxic-Ischemic Encephalopathy (Global Hypoxia-Ischemia)
u Sentinel hypoxic or ischemic event occurring immediately before or during labor and delivery
(eg, placental abruption, uterine rupture, cord prolapse)
u Heart rate monitor patterns consistent with an acute peripartum or intrapartum event
u Apgar score of less than 5 at 5 minutes and 10 minutes
u Fetal umbilical artery pH of less than 7.0 or base deficit of 12 mmol/L or greater
u Onset of encephalopathy within the first 24 hours of life
u Presence of multiorgan failure consistent with hypoxia-ischemia (eg, elevated transaminases,
hypotension/cardiomyopathy, renal failure, bone marrow failure)
Bacterial or Viral Sepsis or Intracranial Infection
u Set up for infection (eg, prolonged rupture of membranes, maternal fever, and chorioamnionitis)
u Mother positive for group B streptococcus
u Temperature instability
u Apnea/bradycardia
u Hypotension
u Hepatic dysfunction including hyperbilirubinemia
u Disseminated intravascular coagulopathy
Ischemic Perinatal Stroke
u Neonate who appears otherwise healthy with focal motor seizures is the most common
clinical presentation
u Focal arterial ischemia on MRI
Intracranial Hemorrhage
u Small subdural hemorrhages are rarely symptomatic
u Intraventricular hemorrhage and periventricular or cerebellar hemorrhages due to fragile
germinal matrix are a common cause of encephalopathy and seizures in preterm neonates
u Intraventricular hemorrhage/thalamic hemorrhage in a term neonate should prompt search for
cerebral sinovenous thrombosis
u Parenchymal hemorrhages in a term neonate may be due to sinovenous thrombosis, trauma,
coagulopathy, vascular malformation, or genetic cause (eg, collagen type IV alpha 1 chain
[COL4A1] mutation), although the cause is often not found

CONTINUED ON PAGE 61

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of hemorrhage. Conventional T1 and T2 images must be evaluated for structural
developmental malformations, as these lesions may cause early encephalopathy
or seizures and may also predispose to secondary hypoxic-ischemic injury during
the birth process.19 DWI can be used to detect anatomic areas of injury in the
acute phase (approximately the first 7 to 10 days after injury). Magnetic
resonance spectroscopy may show a lactate peak (a sign of abnormal metabolism
most often due to acute injury) or low N-acetylaspartate (NAA) (indicating
decreased neuronal integrity).

CONTINUED FROM PAGE 60

Brain Malformation
u Abnormal fetal or neonatal ultrasound or MRI
u Associated craniofacial dysmorphisms or organ anomalies
u Genetic abnormality
Inborn Error of Metabolism
u Cerebral edema or symmetric pattern of injury
u Persistent lactic acidosis
u High ammonia
u Feeding intolerance/vomiting
u Unusual odor
Neonatal-Onset Epileptic Encephalopathy
u Persistent clinical and/or EEG seizures despite medication escalation
u Prominent tonic symptomatology
u EEG with persistent burst suppression
u Worsening clinical status or EEG patterns
u MRI in the first week of life without acute injury
u Gene mutation (eg, KCNQ2, KCNQ3, SCN1A, SCN2A, SLC13A5, STXBP1, KCNT2, GDLC,
CDKL5, CHD7)10
Transient Encephalopathy
u Maternal use of selective serotonin reuptake inhibitors (SSRIs), serotonin norepinephrine
reuptake inhibitors (SNRIs), drugs of abuse
u Electrolyte abnormality
u Hypoglycemia

EEG = electroencephalogram; MRI = magnetic resonance imaging.

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HYPOXIC-ISCHEMIC ENCEPHALOPATHY

FIGURE 3-1
Concurrent EEG and amplitude-integrated EEG in two neonates with presumed hypoxic-ischemic
encephalopathy. Neonatal EEG montage is displayed at 15 mm/sec and with sensitivity of
7 µV/mm (A) and 15 µV/mm (B). Amplitude-integrated EEG time scale is noted with each
compressed trace, representing more than 3 hours of recording. A, Upper panel of normal
continuous EEG and amplitude-integrated EEG shows normal continuous voltage with cycling
in a neonate with encephalopathy presumed to be caused by hypoxic-ischemic encephalopathy
who is status post–therapeutic hypothermia. B, Lower panel showing neonate with
encephalopathy presumed due to be caused by hypoxic-ischemic encephalopathy. The
seizure arising from T4 on the EEG is evident as a sudden rise in the lower and upper margins
of the suppressed amplitude-integrated EEG.

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MRI is an important prognostic tool, as the pattern and severity of injury
are helpful in predicting later deficits. For neonates who receive therapeutic
hypothermia, the burden of injury apparent on MRI is lower, particularly in basal
ganglia and thalamus but also in the white matter and watershed regions.20–22
MANAGEMENT OF THE ENCEPHALOPATHIC NEONATE
Neonates with encephalopathy should be cared for in a neonatal intensive care
unit with capacity to provide neuromonitoring, neuroimaging, and subspecialty
neurologic care.
Neurocritical Care
Advances in basic cardiopulmonary support, favorable evidence from the adult
neurocritical care literature, and improved understanding of the impact of
critical illness on the developing brain have led to the emergence of neonatal
neurocritical care (also called neonatal neurointensive or brain-focused care) as
an important approach that can potentially improve developmental outcomes in
neonates with encephalopathy.23 The focus of neonatal neurocritical care
involves a culture change for the entire neonatal intensive care unit toward
brain-focused care, such that all care providers are continually aware of the
neurologic implications of critical illnesses and the impact of management
strategies on the developing brain.24,25 For example, optimized care involves
active management of temperature (including therapeutic hypothermia for
neonates with encephalopathy due to hypoxia-ischemia and avoiding hyperthermia
for all brain-injured neonates),26 blood pressure (to avoid fluctuations in brain
perfusion in the setting of critical illness and pressure passive circulation),
oxygenation/ventilation, and glucose (especially avoiding hypoglycemia, which
can cause de novo injury and may exacerbate underlying hypoxic-ischemic
injury).27–29 This attention to physiologic homeostasis is especially important
during resuscitation and the so-called “golden” first hour after delivery.30
In addition to medical management, application of advanced technologies such
as digital EEG with bedside trending (such as amplitude-integrated EEG) and
remote review allow bedside assessment of brain function in real time. Furthermore,
safe, high-resolution brain imaging using MRI is widely available as an important
tool to assess the impact of critical illness on brain structure and development.
A focus on the brain during the period of critical illness allows for medical
interventions, including application of therapeutic hypothermia and treatment
of seizures in real time, developmentally supportive care, compassionate
communication with families, and, if appropriate, early decision making
regarding goals of care. According to the literature on acute brain injury in adults,
a neurocritical care approach leads to higher rates of favorable outcomes by the
following mechanisms: (1) earlier recognition and treatment of neurologic
conditions; (2) prevention of secondary brain injury through attention to
maintenance of physiologic homeostasis of factors such as temperature, blood
pressure, and glucose; (3) consistent management using guidelines and protocols;
and (4) use of experienced specialized teams at dedicated referral centers.31

KEY POINTS
● The American Clinical
Neurophysiology Society
recommends
neurophysiologic monitoring
using continuous EEG or
amplitude-integrated EEG to
determine the presence of
electrographic seizures and
to establish the severity of
encephalopathy.
● MRI is recommended
for all neonates with
encephalopathy or seizures
to assist with identifying the
etiology of encephalopathy,
as well as for assisting
with prognosis.
● Optimized care involves
active management of
temperature (including
therapeutic hypothermia
for neonates with
encephalopathy due to
hypoxia-ischemia and
avoiding hyperthermia for all
brain-injured neonates),
oxygenation/ventilation,
and glucose (especially
avoiding hypoglycemia,
which can cause de
novo injury and may
exacerbate underlying
hypoxic-ischemic injury).
● Therapeutic hypothermia
to 33.5°C (92.3°F) for
72 hours is standard of care
for neonates who are at least
36 weeks gestational age
and who have neonatal
encephalopathy that is due
to suspected or confirmed
hypoxia-ischemia.

Therapeutic Hypothermia for Neonatal Encephalopathy
Therapeutic hypothermia to 33.5°C (92.3°F) for 72 hours is standard of care
for neonates at least 36 weeks gestational age at birth who have neonatal
encephalopathy that is due to suspected or confirmed hypoxia-ischemia.32 The

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HYPOXIC-ISCHEMIC ENCEPHALOPATHY

proposed mechanisms of neuroprotection by hypothermia include suppression
of apoptosis, reduced inflammation and cytotoxic edema, lowered cerebral
metabolism, and modulation of seizure severity.33 Several randomized controlled
trials and meta-analyses demonstrated reduced death or disability at 18 to
24 months of age (relative risk 0.75, 95% confidence interval, 0.68–0.83), a higher
number of children with a normal outcome, and sustained benefits to children
from infancy until they reach school age (although loss to follow-up has been a
significant issue in the large trials).34–36 The number needed to treat to prevent
death or disability is, on average, about 6 to 7. A trial of longer (120 hours) or
deeper (32.0°C [89.6°F]) cooling was terminated early when a futility analysis
determined that the likelihood of benefit of longer or deeper cooling (or both) for
neonatal death was less than 2%.37
Eligibility criteria varied slightly between the clinical trials and typically
involved some combination of gestational age (generally 36 weeks or more,
although one study cooled neonates at 35 weeks), indicator of perinatal distress
(an Apgar score of less than 5 at 10 minutes, blood gas pH of less than 7.00 or
base excess of −12 mmol/L to −16 mmol/L or more from the umbilical cord or
within the first hour of life, or more than 10 minutes of resuscitation), and
moderate to severe encephalopathy. Some regional systems have implemented
screening criteria for when to call a cooling center to improve identification of
eligible neonates.
Therapeutic hypothermia should be implemented within 6 hours after birth, and
evidence from preclinical studies and the randomized controlled trials suggests
that earlier implementation leads to lower rates of death or moderate/severe
disability.38–40 Disability is variably defined depending on the trial and is typically
some combination of low scores on standardized cognitive testing, functionally
disabling cerebral palsy, epilepsy, and vision or hearing impairment.41
Passive cooling can be safely initiated prior to transport; servo-controlled
devices that help to maintain stable temperature and avoid overcooling are
available for use during transport.42 Both head cooling and whole-body cooling
appear equally effective.34 Whole-body cooling has been preferentially adopted due
to the ready availability of cooling blankets at many centers, as well as better access
to the infant’s head for brain monitoring using EEG. Many centers use sedation
(eg, with morphine sulfate) to prevent discomfort, cold stress, and shivering.
Continuous brain monitoring, preferably with continuous video-EEG, is
recommended for all neonates undergoing hypothermia.11 The risk of seizures in
neonates undergoing hypothermia is approximately 50%.43–45 Seizures most
commonly arise within the first 24 hours of life and should be treated as rapidly
as possible after detection using adequate doses of antiseizure medications.
Phenobarbital (20 mg/kg initial dose) and phenytoin (or preferably fosphenytoin
at 20 mg/kg of phenytoin equivalents) have similar efficacy; however, approximately
one-half of children have recurrent seizures after the initial bolus of either
medication.46 Levetiracetam is also used to treat seizures in neonates (40 mg/kg
to 60 mg/kg initial dose); however, limited data exist regarding efficacy. In the
case of recurrent seizures, escalating doses of antiseizure medications are warranted
to abolish electrographic seizures (including those without clinical correlate).
Recurrent (or rebound) seizures have been reported during the rewarming phase
of therapeutic hypothermia, although this phenomenon appears to be relatively
uncommon.47 In the setting of acute symptomatic seizures due to HIE, prolonged
treatment is rarely warranted. Although limited evidence exists to guide duration

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of treatment, in almost all cases,
antiseizure medications can safely
be discontinued once the acute
symptomatic seizures
have resolved.48,49
EEG is prognostic for brain
injury and developmental
outcomes in neonates undergoing
hypothermia. Normal or mildly
abnormal EEG (eg, mild excess
discontinuity) or early recovery
from severe abnormalities within
the first 24 to 36 hours after birth
portends good prognosis, whereas
severe (and especially persistently
severe) abnormalities (eg, burst
suppression, depressed and
FIGURE 3-2
undifferentiated tracing, extremely Apparent diffusion coefficient map on the fourth
low voltage) are associated with
day after birth in a full-term neonate born by
cesarean delivery after maternal uterine rupture
moderate to severe brain injury,
50–52
shows reduced diffusion in the ventrolateral
death, and disability.
thalamus, basal ganglia, motor cortex,
MRI is recommended for all
hippocampus, and brainstem.
neonates undergoing
hypothermia to assist with
determining etiology of
encephalopathy, timing of injury, and prognosis. The predominant patterns of
injury in neonates with HIE are (1) basal ganglia/thalamus (with extension to
rolandic cortex, hippocampus, and brainstem in severe cases), which is seen
predominantly in the setting of acute profound disruption in placental
perfusion FIGURE 3-2, and (2) watershed areas (with injury to the watershed
zones of the anterior, middle, and posterior cerebral arteries), which occurs in
the setting of partial prolonged disruption of placental perfusion (CASE 3-1 and
53
CASE 3-2).
Hypothermia is associated with reduced extent of injury on MRI, especially
injury to the thalamus and basal ganglia.20,21 MRI is useful to ensure that
the diagnosis of HIE is, in fact, correct given that children with underlying
anomalies are at higher risk for peripartum asphyxia and imaging may reveal
unexpected findings such as brain malformations.19,54 In addition, the MRI
provides useful prognostic information (TABLE 3-255–60).20,59 Children
with injury to the thalamus or basal ganglia typically develop cerebral palsy,
whereas outcome for children with the watershed pattern of injury is
variable, and outcome may be favorable even in children with severe injury.57,60

KEY POINTS
● Eligibility criteria in
clinical trials for therapeutic
hypothermia for neonatal
encephalopathy varied
slightly between trials and
typically involved some
combination of gestational
age, indicator of perinatal
distress, and moderate to
severe encephalopathy.
● Therapeutic hypothermia
should be implemented
within 6 hours after birth,
and evidence from
preclinical studies and the
randomized controlled trials
suggests that earlier
implementation leads to
better outcomes.
● Continuous brain
monitoring, preferably
with continuous video-EEG,
is recommended for all
neonates undergoing
hypothermia.
● The risk of seizures in
neonates undergoing
hypothermia is
approximately 50%.
● Normal or mildly
abnormal EEG (eg, mild
excess discontinuity) or
early recovery of severe
abnormalities within the first
24 to 48 hours after birth
portends good prognosis,
whereas severe (and
especially persistently
severe) abnormalities
(eg, burst suppression,
depressed and
undifferentiated tracing,
extremely low voltage) are
associated with brain injury,
death, and disability.

Alternative and Adjuvant Neuroprotective Agents
Multiple alternative and adjuvant agents that target various mechanisms in
the cascade of events that lead to neuronal necrosis and apoptosis are under
investigation in preclinical and clinical studies.61,62 Examples of target mechanisms
and agents include (1) preventing free radical–induced injury (eg, antioxidants
such as melatonin, allopurinol, and N-acetylcysteine), (2) reducing excitotoxicity
(eg, xenon, magnesium sulfate, cannabinoids), (3) anti-inflammation, and

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HYPOXIC-ISCHEMIC ENCEPHALOPATHY

(4) repair and regeneration (eg, erythropoietin, stem cells). These agents are
currently being evaluated in preclinical or clinical trials and are not in widespread
clinical use.
Prognosis
Neonates with encephalopathy are at risk for long-term disabilities, including
cerebral palsy, epilepsy, and cognitive impairment. The predictors of unfavorable
outcomes are indicated in TABLE 3-2. Therapeutic hypothermia does not prevent
adverse outcomes in all patients. The rate of death or disabilities in the
randomized controlled trials was approximately 50%.63 Similarly, the rates of
cerebral palsy and developmental delay are lower among cooled neonates; however,
they remain approximately 19% for cerebral palsy and 23% for developmental delay.

CASE 3-1

An infant girl was born at 39 weeks gestation by emergent cesarean
delivery due to maternal placental abruption. Apgar scores were assigned
as 0 at 1 minute, 2 at 5 minutes, 2 at 10 minutes, and 5 at 15 minutes. Cord
arterial pH was 6.90 with base deficit 17 mmol/L. The initial neurologic
examination 60 minutes after birth was remarkable for decreased
responsiveness, absent suck/gag, generalized hypotonia, and
stereotyped response to noxious stimuli.
Therapeutic hypothermia was initiated for treatment of suspected
hypoxic-ischemic encephalopathy (HIE) due to placental abruption. The
target temperature was achieved by 2 hours after birth. The initial EEG
was discontinuous with interburst intervals of up to 17 seconds and
without obvious state changes. Fourteen hours after birth, the infant
experienced four focal seizures lasting 45 to 60 seconds each that
stopped following a single dose of IV phenobarbital (20 mg/kg).
By the day after birth, the infant had spontaneous eye opening and was
more responsive. The EEG had improved, showing only mild excess
discontinuity with interburst intervals of up to 8 seconds during sleep.
Phenobarbital was discontinued. MRI performed the fourth day after
birth was normal, including diffusion-weighted imaging (DWI) and
magnetic resonance spectroscopy with a voxel placed in the left basal
ganglia. The child was taking full oral feeds via breast-feeding by the fifth
day after birth and was discharged home on the seventh day after
showing adequate oral intake. Prior to discharge home, the parents were
counseled regarding a cautiously optimistic prognosis based on early
improvement of EEG and neurologic examination as well as the normal
MRI. At age 2, the child had normal development and had not had
recurrent seizures.

COMMENT

This case demonstrates the importance of implementing therapeutic
hypothermia at the earliest possible time after recognition of HIE. This case
also demonstrates the prognostic value of early improvement of the EEG
and of normal MRI, as well as the possibility of good outcomes after HIE
even in children with severe acidosis and low Apgar scores.

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Reasons for absent or incomplete effect of hypothermia may be delayed onset of
cooling, injury that is too severe, or incorrect diagnosis.
MANAGEMENT OF ENCEPHALOPATHY NOT DUE TO HYPOXIC-ISCHEMIC
ENCEPHALOPATHY
If HIE is not the cause of the encephalopathy, then the general neurocritical care
principles discussed above (eg, maintaining normal glucose, temperature, blood
pressure) apply; however, therapeutic hypothermia is not indicated. Neonates
with suspected infection as the cause of encephalopathy should be treated with
antimicrobial agents (or antiviral agents if herpes simplex virus is suspected).
Neonates with arterial stroke should have a careful cardiac examination to assess
for congenital heart defects and a family history taken to assess for risk factors for
thrombophilia. Neonates with bland or hemorrhagic venous infarcts should be
reimaged within 1 week and consideration given for anticoagulation if an acute
clot is identified.64,65 In the setting of neonatal encephalopathy due to brain
malformation, a suspected or confirmed inborn error of metabolism, or
neonatal-onset epileptic encephalopathy, a specific genetic diagnosis should
be sought.

KEY POINT
● The predominant
patterns of injury in
neonates with hypoxicischemic encephalopathy
are (1) basal ganglia/
thalamus (with extension to
rolandic cortex,
hippocampus, and
brainstem in severe cases,
which is seen predominantly
in the setting of acute
profound disruption in
placental perfusion), and (2)
watershed areas (with injury
to the watershed zones of
the anterior, middle, and
posterior cerebral arteries),
which occurs in the setting
of partial prolonged injuries.

A 37-year-old woman with gestational diabetes mellitus and
hypertension who was pregnant with a 41-week-gestation male fetus
presented to obstetric triage because of decreased fetal movements
during the previous 12 hours. Labor was induced, and after 24 hours of
induction, the fetal heart monitor showed bradycardia to 60 beats/min,
and the child was delivered emergently by cesarean delivery. The child
was limp, apneic, and bradycardic at birth. Apgar scores were assigned as
1 at 1 minute, 2 at 5 minutes, and 4 at 10 minutes. The child was intubated
and transferred to a regional cooling center. During transport, the child
had several episodes of asymmetric tonic stiffening with changes in vital
signs and was treated with 20 mg/kg of IV phenobarbital followed by
maintenance dosing for presumed seizures.
Cooling was initiated at 5 hours after birth. EEG initiated at 10 hours
after birth showed status epilepticus without clinical correlate. The child
received an additional 20 mg/kg of phenobarbital, after which he was
unresponsive, and the background EEG pattern showed no definite
cerebral activity. This EEG pattern persisted throughout cooling and
rewarming. An MRI on the fifth day after birth showed injury to the
thalamus, basal ganglia, and much of the cerebral cortex and subcortical
white matter. Magnetic resonance spectroscopy showed a large lactate
peak and low N-acetylaspartate (NAA) in the basal ganglia. The parents
were counseled regarding expected poor prognosis, and they chose to
discontinue life support and provide the child with palliative care.

CASE 3-2

This case exemplifies several key indicators of a poor prognosis in neonates
with hypoxic-ischemic encephalopathy: status epilepticus, persistently
severely abnormal EEG, and severe injury on MRI.

COMMENT

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HYPOXIC-ISCHEMIC ENCEPHALOPATHY
KEY POINTS
● Developmental care by
occupational and physical
therapists and lactation
experts can begin during the
inpatient admission to assess
and manage positioning, oral
feeding readiness and
preparation, and behavioral
state regulation and to
optimize tone, strength, and
ability to deal with
environmental stimuli.
● Since survivors of
neonatal encephalopathy
are at high risk for long-term
disabilities, children should
be followed longitudinally
by a high-risk program or
a child neurologist as
recommended by the
American Academy
of Pediatrics.

LONG-TERM MANAGEMENT
Once the neonate with encephalopathy has recovered from the critical illness, the
focus turns toward establishing oral feeding and readiness for discharge home.
Developmental care by occupational and physical therapists and lactation
experts can begin during the inpatient admission to assess and manage
positioning, oral feeding readiness and preparation, and behavioral state
regulation and to optimize tone, strength, and ability to deal with environmental
stimuli.24 Developmentally appropriate exercises (eg, upright positioning,
“tummy time,” language exposure, and early exposure to fine motor tasks) can
be initiated in the hospital and taught to the parents for practice at home.
Since survivors of neonatal encephalopathy are at high risk for long-term
disabilities, children should be followed longitudinally by a high-risk program or
a child neurologist as recommended by the American Academy of Pediatrics.32
Close monitoring ensures appropriate and timely referrals to developmental
therapies such as occupational and physical therapy. Follow-up should be at
least until 18 to 24 months of age; however, follow-up until school age is preferred.

CONCLUSION
Neonatal encephalopathy is a heterogeneous disorder marked by altered mental
status, altered muscle tone, and depressed primitive reflexes, as well as
seizures. Therapeutic hypothermia is standard of care for neonates with
encephalopathy that is presumed to be caused by hypoxia-ischemia and who
would have fulfilled entry criteria into the large randomized trials. Brain-focused

Predictors of Outcome in Neonates Treated With Therapeutic Hypothermia

TABLE 3-2

Indicators of Poor Prognosis

Indicators of Good Prognosis

Clinical examination

Unresponsive, minimally responsive, or stereotyped responsiveness No or mild encephalopathy at
persisting beyond 24–36 hours after birth
24 hours55

EEG/amplitudeintegrated EEG

Severe abnormality (burst suppression, depressed and
undifferentiated tracing, extremely low voltage on continuous EEG;
burst suppression or flat tracing on amplitude-integrated EEG),
especially if it persists beyond 24–36 hours after birth50–52
Seizures that are refractory to initial loading doses of antiseizure
medications or multifocal56

Early normalization of EEG/
amplitude-integrated EEG
(within 24–36 hours)
Early return of sleep-wake
cycling
Seizures that respond to
first-line medication

MRI

Moderate to severe injury (and especially near-total injury)
Injury to the ventrolateral thalamus or basal ganglia57
Absent myelination of the posterior limb of the
internal capsule58

Children with focal or
watershed pattern of injury,
even with high injury burden,
may have a favorable outcome60

Magnetic resonance spectroscopy lactate: N-acetylaspartate
that is greater than 1/359

EEG = electroencephalogram; MRI = magnetic resonance imaging.

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management includes neurophysiologic monitoring and imaging with MRI to
help determine diagnosis, prognosis, and neurologic complications, as well as
careful attention to maintenance of normal homeostatic mechanisms (eg, glucose,
blood pressure) to help prevent secondary brain injury. While outcomes have
improved since the widespread use of hypothermia, risk of death or disability in
the clinical trials was almost 50%. Emerging adjuvant therapies such as
erythropoietin hold promise for further improving outcomes.

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