{
 "topic": "Hypoxic-Ischemic Encephalopathy",
 "slug": "hypoxic-ischemic-encephalopathy",
 "category_id": 15349,
 "summary": "Mechanism, staging, and management of hypoxic-ischemic encephalopathy, the leading cause of neonatal brain injury worldwide.",
 "written_by": "claude-sonnet",
 "references": [
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 ],
 "short": [
  {
   "title": "In short",
   "content": "- Hypoxic-ischemic encephalopathy (HIE) is brain injury from inadequate oxygen and/or blood flow, most often perinatal (placental/umbilical gas exchange failure or postnatal respiratory depression), but can also occur later from cardiopulmonary arrest (drowning, shock, poisoning, arrhythmia).\n- Incidence in high-income countries is roughly 0.5\u20131 to 8 per 1000 term live births (estimates vary by source); in low/middle-income countries it can reach 26 per 1000. HIE is the most common cause of neonatal seizures, accounting for about 60% of cases with onset in the first 24 hours.\n- Birth asphyxia causes an estimated 23% of neonatal deaths worldwide.\n- Injury evolves in two phases: primary energy failure (ATP depletion, lactate accumulation, failure of Na/K and Ca pumps causing cellular/cerebral edema) followed by a secondary phase during reperfusion \u2014 much of the damage occurs during reperfusion, not the initial insult.\n- Levene staging: mild (irritable, hypotonia, no seizures, poor suck), moderate (lethargic, marked hypotonia, seizures, unable to suck), severe (comatose, severe hypotonia, prolonged seizures, unable to sustain spontaneous respiration).\n- Diagnosis requires an acute perinatal event (e.g., cord prolapse, placental abruption), an abnormal standardized neurologic exam, low Apgar scores, and evidence of acidosis on cord or early infant blood gas.\n- Multi-organ dysfunction commonly accompanies encephalopathy: persistent pulmonary hypertension of the newborn, myocardial dysfunction/hypotension, hypoglycemia, hypocalcemia, hyponatremia, renal failure, and disseminated intravascular coagulation (DIC).\n- Neuropathology differs by gestational age: preterm infants show periventricular leukomalacia and periventricular hemorrhage/infarction; term infants show selective cortical neuronal necrosis, status marmoratus of basal ganglia/thalamus, and parasagittal cerebral injury.\n- Therapeutic hypothermia is standard of care for moderate-to-severe HIE in the UK and many other countries."
  }
 ],
 "long": [
  {
   "title": "Definition",
   "content": "Hypoxemia is a decreased arterial oxygen concentration, which frequently produces hypoxia (decreased oxygen delivery to cells/organs); ischemia is blood flow inadequate to maintain physiologic function. Hypoxic-ischemic encephalopathy (HIE) is the resulting brain injury when systemic hypoxemia and/or reduced cerebral blood flow deprive the brain of oxygen. In the neonate this typically follows a perinatal event that prevents adequate blood or oxygen supply to the infant brain; the term \"birth asphyxia\" carries medicolegal weight and should be reserved for infants with clinical features of HIE plus documented evidence of severe hypoxia antenatally, during labor, or at delivery. HIE can also occur outside the perinatal period as a consequence of cardiopulmonary arrest at any age."
  },
  {
   "title": "Epidemiology",
   "content": "HIE is a leading global cause of neonatal brain injury, morbidity, and mortality. Estimates of incidence vary by setting: roughly 0.5\u20131 per 1000 term live births in high-income countries, with some sources citing up to 8 per 1000 in the developed world, versus as high as 26 per 1000 in developing regions. Significant long-term neurologic disability follows in about 0.3 per 1000 term live-born infants in high-income countries. Birth asphyxia is estimated to cause 23% of neonatal deaths worldwide. Among causes of neonatal seizures, HIE is the most common, responsible for about 60% of cases, typically with onset in the first 24 hours of life."
  },
  {
   "title": "Etiology",
   "content": "Most neonatal HIE follows a significant hypoxic event immediately before or during labor or delivery \u2014 failure of placental or umbilical gas exchange \u2014 or postnatal respiratory depression. Antenatal contributors include chorioamnionitis, placental abruption, nuchal cord, and chronic maternal hypertension. Severe postnatal cardiorespiratory compromise (respiratory or cardiac arrest) can also cause it, and in premature neonates HIE is often associated with intraventricular hemorrhage. Outside the neonatal period, pediatric HIE commonly follows cardiopulmonary arrest from drowning, severe respiratory distress, shock, drug overdose/poisoning, or lethal arrhythmia. The extent of injury depends on the duration and severity of the initial insult plus secondary injury that develops over the following minutes to days after blood flow and oxygen delivery are restored."
  },
  {
   "title": "Pathophysiology",
   "content": "Compromised gas exchange leads to hypoxia, hypercarbia, and metabolic/respiratory acidosis; reduced cardiac output then diminishes tissue perfusion, producing hypoxic-ischemic injury to the brain and other organs. At the cellular level, loss of oxidative metabolism causes primary energy failure: ATP depletion and lactate accumulation halt ATP-dependent sodium/potassium and calcium pumps, raising intracellular sodium and calcium and driving cellular (cerebral) edema through water influx. A secondary injury phase follows during reperfusion of the previously ischemic brain \u2014 much of the ultimate damage occurs at this stage rather than during the initial insult. Neuropathologic patterns differ by maturity: preterm infants tend toward selective subcortical neuronal necrosis, periventricular leukomalacia, and periventricular hemorrhage or infarction, while term infants show selective cortical neuronal necrosis, status marmoratus of the basal ganglia and thalamus, and parasagittal cerebral injury."
  },
  {
   "title": "Clinical features",
   "content": "Severe HIE produces encephalopathy alongside multi-organ dysfunction: abnormal neurologic signs and seizures in the brain; respiratory failure with persistent pulmonary hypertension of the newborn; myocardial dysfunction with hypotension; metabolic derangements including hypoglycemia, hypocalcemia, and hyponatremia; and other organ dysfunction such as renal failure and disseminated intravascular coagulation. The Levene staging system grades severity by consciousness, tone, seizures, and sucking/respiratory ability: mild disease shows an irritable infant with hypotonia, no seizures, and poor suck; moderate disease shows lethargy, marked hypotonia, seizures, and inability to suck; severe disease shows coma, severe hypotonia, prolonged seizures, and inability to sustain spontaneous respiration."
  },
  {
   "title": "Diagnostics",
   "content": "Diagnosis of neonatal HIE generally requires: a history of an acute perinatal event (e.g., cord prolapse, placental abruption), a standardized neurologic examination consistent with encephalopathy, low Apgar scores, and evidence of acidosis on umbilical cord or early infant blood gas. Because the diagnosis of \"birth asphyxia\" has serious medicolegal implications, it should only be applied when there is objective evidence of severe hypoxia antenatally, during labor, or at delivery \u2014 and only after excluding other causes of neonatal encephalopathy, since the clinical picture can otherwise be mimicked by an inborn error of metabolism or kernicterus."
  },
  {
   "title": "Differential diagnosis",
   "content": "Among causes of neonatal seizures/encephalopathy, HIE accounts for roughly 60% of cases (onset in the first 24 hours); other causes to distinguish include intracranial hemorrhage (up to 15%, periventricular/intraventricular, subdural, subarachnoid, or stroke), infection (12%), hypoglycemia (small for gestational age, infant of a diabetic mother), hypocalcemia/hypomagnesemia (low birth weight, infant of a diabetic mother), hyponatremia (rare, SIADH), amino/organic acid disorders with hyperammonemia, pyridoxine-dependent seizures (refractory seizures that resolve with pyridoxine), developmental/chromosomal anomalies, and drug withdrawal; about 10% of cases have no cause found. Imaging differentials include germinal matrix hemorrhage and mitochondrial encephalopathies."
  }
 ],
 "clinical": [
  {
   "title": "Management",
   "content": "Therapeutic hypothermia has become the standard of care for moderate or severe neonatal HIE in the UK and many other countries and should be considered promptly once the diagnosis is suspected in an infant meeting perinatal-event, examination, Apgar, and blood-gas-acidosis criteria. Because much of the ultimate brain injury occurs during the secondary, reperfusion phase rather than the initial insult, early recognition and supportive stabilization matter: support respiration (these infants may be unable to sustain spontaneous respiration in severe disease), support blood pressure/cardiac output given the risk of myocardial dysfunction and hypotension, and correct the metabolic derangements that commonly accompany HIE \u2014 hypoglycemia, hypocalcemia, and hyponatremia. Monitor for and manage seizures, and evaluate for coexisting multi-organ dysfunction (renal failure, DIC, persistent pulmonary hypertension of the newborn) since these commonly accompany severe encephalopathy. Staging severity (e.g., by the Levene system \u2014 consciousness, tone, presence/duration of seizures, ability to suck or sustain respiration) helps track clinical trajectory. Long-term follow-up is essential given the substantial risk of neurologic disability after moderate-to-severe HIE."
  }
 ]
}