HYPOXIC ISCHEMIC ENCEPHALOPATHY
Category: Child Health
Abstract : History (hypoxic ischemic encephalopathy): Per the guidelines of the AAP and ACOG, all of the following must be present for the designation of asphyxia. However, infants may have experienced asphyxia or brain hypoxia remote from the time of delivery and exhibit the signs and symptoms of hypoxic encephalopathy at the time of birth. • Profound metabolic or mixed acidemia (pH <7.00) in
History (hypoxic ischemic encephalopathy):
Per the guidelines of the AAP and ACOG, all of the following must be present for the designation of asphyxia. However, infants may have experienced asphyxia or brain hypoxia remote from the time of delivery and exhibit the signs and symptoms of hypoxic encephalopathy at the time of birth.
• Profound metabolic or mixed acidemia (pH <7.
00) in an umbilical artery blood sample, if obtained
• Persistence of an Apgar score of 0-3 for longer than 5 minutes
• Neonatal neurologic sequelae (eg, seizures, coma, hypotonia)
• Multiple organ involvement (eg, of the kidney, lungs, liver, heart, intestines)
• On rare occasions, difficulties with delivery, particularly problems with delivering the "after-coming" head in breech presentation, suggest an alternate diagnosis of hemorrhage in the posterior cerebral fossa, which is a rare condition.
Physical (hypoxic ischemic encephalopathy):
Clinical manifestations and course vary depending on HIE severity.
• Mild HIE
o Muscle tone may be increased slightly and deep tendon reflexes may be brisk during the first few days.
o Transient behavioral abnormalities, such as poor feeding, irritability, or excessive crying or sleepiness, may be observed.
o By 3-4 days of life, the CNS examination findings become normal.
• Moderately severe HIE
o The infant is lethargic, with significant hypotonia and diminished deep tendon reflexes.
o The grasping, Moro, and sucking reflexes may be sluggish or absent.
o The infant may experience occasional periods of apnea.
o Seizures may occur within the first 24 hours of life.
o Full recovery within 1-2 weeks is possible and is associated with a better long-term outcome.
o An initial period of well-being may be followed by sudden deterioration, suggesting reperfusion injury; during this period, seizure intensity might increase.
• Severe HIE
o Stupor or coma is typical. The infant may not respond to any physical stimulus.
o Breathing may be irregular, and the infant often requires ventilatory support.
o Generalized hypotonia and depressed deep tendon reflexes are common.
o Neonatal reflexes (eg, sucking, swallowing, grasping, Moro) are absent.
o Disturbances of ocular motion, such as a skewed deviation of the eyes, nystagmus, bobbing, and loss of "doll's eye" (ie, conjugate) movements may be revealed by cranial nerve examination.
o Pupils may be dilated, fixed, or poorly reactive to light.
o Seizures occur early and often and may be initially resistant to conventional treatments. The seizures are usually generalized, and their frequency may increase during the 2-3 days after onset, correlating with the phase of reperfusion injury. As the injury progresses, seizures subside and the EEG becomes isoelectric or shows a burst suppression pattern. At that time, wakefulness may deteriorate further, and the fontanelle may bulge, suggesting increasing cerebral edema.
o Irregularities of heart rate and BP are common during the period of reperfusion injury, as is death from cardiorespiratory failure.
• Infants who survive severe HIE
o The level of alertness improves by days 4-5 of life.
o Hypotonia and feeding difficulties persist, requiring tube feeding for weeks to months.
• Involvement of multiple organs besides the brain is a hallmark of HIE.
o Severely depressed respiratory and cardiac functions and signs of brainstem compression suggest a life-threatening rupture of the vein of Galen (ie, great cerebral vein) with a hematoma in the posterior cranial fossa.
o Reduced myocardial contractility, severe hypotension, passive cardiac dilatation, and tricuspid regurgitation are noted frequently in severe HIE.
o Patients may have severe pulmonary hypertension requiring assisted ventilation.
o Renal failure presents as oliguria and, during recovery, as high-output tubular failure, leading to significant water and electrolyte imbalances.
o Intestinal injuries may not be apparent in the first few days of life. Poor peristalsis and delayed gastric emptying are common; necrotizing enterocolitis occurs rarely.
Lab Studies (hypoxic ischemic encephalopathy):
No specific test excludes or confirms a diagnosis of HIE. The diagnosis is based on the history and physical examination. All tests are performed to assess the severity of brain injury and to monitor the functional status of systemic organs. Choice of tests depends on the evolution of symptoms. As with any other disease, test results should be interpreted in conjunction with clinical history and the findings of physical examination.
o Serum electrolytes:
In those affected by severe HIE, daily assessment of serum electrolytes would be of value until the infant's status improves. Markedly low serum sodium, potassium, and chloride in the presence of reduced urine flow and excessive weight gain may indicate acute tubular damage or inappropriate antidiuretic hormone (IADH), particularly during the initial 2-3 days of life.
o Similar changes during recovery, with increased urine flow, might indicate ongoing tubular damage and excessive sodium loss relative to water loss.
o Renal function studies:
Serum creatinine, creatinine clearance, and BUN suffice in most cases.
Imaging Studies (hypoxic ischemic encephalopathy):
• Since, in most HIE cases, imaging studies are inconsistent in revealing abnormal findings, a normal imaging study finding cannot be used to rule out HIE.
• Cranial ultrasound:
Ultrasound is portable and provides a quick assessment of brain lesions. Although it reveals intracranial hemorrhages and cerebral edema (decreased ventricular size), it is not ideal for detailed mapping of the posterior cranial fossa.
• CT scan of the head:
This study, especially if done with contrast infusion, may reveal evidence of cerebral edema (eg, obliteration of cerebral ventricles, blurring of sulci) manifested as narrowness of the lateral ventricles and flattening of gyri. Areas of reduced density might indicate regions of infarction. Rarely, evidence of hemorrhage in the ventricles may be seen.
o In suspected posterior cranial fossa hemorrhage, CT scan must be obtained as soon as clinically feasible because early diagnosis helps in obtaining early neurosurgical consultation.
o Intracranial hemorrhage is a rare finding in term infants; however, cerebral artery occlusions and infarctions can be diagnosed with radiographic imaging studies.
• MRI is valuable in moderately severe and severe HIE, particularly to note the status of myelination, white-grey tissue injury, and to identify preexisting developmental defects of the brain. MRI is also useful during follow-up. In any newly diagnosed case of cerebral palsy, MRI should be considered, since it may help in establishing the cause. However, the interpretation of MRI in infants requires considerable expertise.
• Echocardiography:
In infants requiring inotropic support, echocardiography (ECHO) helps to define myocardial contractility and the existence of structural heart defects, if any.
Other Tests:
• Choice of tests depends on the evolution of symptoms.
• EEG:
Even in the absence of obvious seizures, EEG should be obtained early, particularly in moderately severe and severe cases. In infants on assisted ventilation, drugs such as pancuronium bromide (for muscle paralysis) and morphine (for sedation) may mask the symptoms of early seizures.
o Generalized depression of the background rhythm and voltage, with varying degrees of superimposed seizures, are the early findings.
o A burst suppression pattern (ie, isoelectric EEG) is particularly ominous. If clinically correlated, this EEG pattern usually is regarded as representing irreversible brain injury, akin to the legal definition of brain death.
• Special sensory evaluation:
Screening for hearing is now mandatory in many states in the United States; in infants with HIE, a full-scale hearing test is preferable because of an increased incidence of deafness among HIE infants requiring assisted ventilation.
• Retinal and ophthalmic examination:
This examination may be valuable, particularly as part of an evaluation for developmental abnormalities of the brain.
Histologic Findings:
The neuropathology of neonatal HIE varies considerably. Depending on the cause of HIE, more than one type of lesion may be seen in a single patient. Brain maturity at the time of the insult is an important factor in the evolution of neuropathology. In the preterm infant, the damage is at the germinal matrix area, leading to hemorrhage in the subependymal region, the germinal matrix, or the intraventricular region. In the full-term infant, the pathology is mainly in the cerebral cortex and in the basal ganglia. Selective neuronal necrosis is the most common neuropathology. Major sites of necrosis are the cerebral cortex, diencephalon, basal ganglia, brain stem, and cerebellum. The injuries correlate with clinical symptoms, such as disturbances of consciousness, seizures, hypotonia, oculomotor-vestibular abnormalities, and feeding difficulties.
• Parasagittal cerebral necrosis:
This lesion is bilateral, usually symmetrical, and occurs in the cerebral cortex and the subcortical white matter, especially in the parietooccipital sides. These regions represent the border zones of perfusion from major cerebral arteries.
• Status marmoratus:
In this lesion, the basal ganglia, especially the caudate nucleus, putamen, and thalamus, demonstrate neuronal loss, gliosis, and hypermyelination, leading to a marble white discoloration of these regions. This is the least common type of neuropathology, and its full evolution may take months to years.
• Focal and multifocal ischemic brain necrosis:
These lesions are relatively large, localized areas of necrosis of cerebral parenchyma, cortex, and subcortical white matter. The most frequently affected region is the zone perfused by the middle cerebral artery.
• Periventricular leukomalacia:
This lesion is characterized by necrosis of white matter, which is seen grossly as white spots adjacent to the external angle of the lateral ventricles. These sites are the border zones between penetrating branches of major cerebral arteries. These lesions are more common in preterm than in term infants.
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