Perinatal Asphyxia

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Introduction & Causes - Gasping for Air

  • Perinatal Asphyxia: Impaired gas exchange (placental/pulmonary) → hypoxemia, hypercapnia, metabolic acidosis.
  • Key Risk: Hypoxic-Ischemic Encephalopathy (HIE).
  • Etiology:
    • Antenatal Factors:
      • Maternal causes: Severe pre-eclampsia, APH, DM, HTN, anemia, sepsis.
      • Placental/Cord issues: Insufficiency, abruption, previa, prolapse, compression.
    • Intrapartum Events:
      • Prolonged/obstructed labor, uterine rupture, shoulder dystocia.
    • Postnatal Conditions:
      • Neonatal problems: Severe RDS, PPHN, CHD, sepsis, MAS.

⭐ Intrapartum sentinel hypoxic events (e.g., cord prolapse, uterine rupture) are major preventable causes of severe asphyxia.

Pathophysiology - Brain Under Siege

  • Initial Insult: Perinatal Hypoxia-Ischemia (HI) initiates a biphasic cascade of neuronal injury.
  • Primary Energy Failure (minutes post-HI):
    • ↓O₂ & glucose → rapid ↓ATP; anaerobic glycolysis causes lactic acidosis.
    • Na⁺/K⁺-ATPase pump failure → ionic imbalance, cytotoxic edema.
    • Excitotoxicity: Massive glutamate release → NMDA/AMPA overactivation → toxic $Ca^{2+}$ influx, early cell damage.
  • Latent Phase (1-6 hours):
    • Brief, partial recovery of oxidative metabolism; crucial therapeutic window.
  • Secondary Energy Failure (6-72 hours post-HI):
    • Reperfusion injury: Mitochondrial dysfunction, ↑Reactive Oxygen Species (ROS), neuroinflammation (cytokines, microglia).
    • Apoptotic pathways are activated, leading to delayed neuronal death.

⭐ Deep gray matter (basal ganglia, thalamus), brainstem, and hippocampus show selective vulnerability.

Patterns of HIE on neonatal brain MRI (DWI and ADC)

Clinical Features & Diagnosis - Spotting the Struggle

  • Immediate Signs (At Birth):
    • Delayed/absent cry, gasping, or apnea.
    • Abnormal tone: initial flaccidity, later hypertonia/opisthotonus.
    • Depressed primitive reflexes (e.g., Moro, suck).
    • Bradycardia (HR < 100 bpm) or severe cyanosis despite oxygen.
  • Evolving Signs (Hypoxic-Ischemic Encephalopathy - HIE):
    • Seizures: often subtle (e.g., lip-smacking, eye deviation) or generalized, typically within 6-24 hours.
    • Altered consciousness: irritability, lethargy, coma.
    • Feeding difficulties, abnormal cry (high-pitched or weak).
  • Diagnosis:
    • Apgar scores: < 7 at 5 minutes suggests asphyxia; < 3 at 5 minutes indicates severe asphyxia.
    • Umbilical cord arterial blood gas: pH < 7.0 and/or base deficit (BD) ≥ 12 mmol/L.
    • Sarnat & Sarnat staging for HIE severity (clinical & EEG findings).
    • Neuroimaging: Cranial Ultrasound (early), MRI (more sensitive for extent of injury, typically day 3-5).
    • Monitor for multi-organ dysfunction (renal, hepatic, cardiac).

⭐ Profound metabolic or mixed acidemia (pH < 7.0 or base deficit ≥ 12 mmol/L) in umbilical cord arterial blood is a cornerstone for diagnosing intrapartum asphyxia.

Management - Cooling to Conquer

  • Initial Resuscitation (ABCDE):
    • Secure Airway, ensure Breathing (O2, PPV), maintain Circulation (IVF, inotropes).
    • Correct metabolic acidosis, hypoglycemia.
    • Seizure control: Phenobarbitone 20 mg/kg IV.
  • Therapeutic Hypothermia (TH):
    • Criteria: ≥36 wks GA, ≥1800g BW, within 6 hrs of birth, mod-severe HIE (Sarnat II/III).
    • Target temp: 33.5-34.5°C for 72 hrs.
    • Rewarm slowly: 0.5°C/hr.
    • Methods: Whole-body/selective head cooling. Neonatal Therapeutic Hypothermia Cradle Layers
  • Supportive Care:
    • Maintain normoglycemia, electrolytes (Ca, Mg).
    • Fluid restriction, monitor renal function.
    • Minimal handling.

⭐ Therapeutic hypothermia is the cornerstone neuroprotective strategy, significantly reducing death or major neurodevelopmental disability in infants with moderate to severe HIE.

Complications & Prognosis - Echoes of Hypoxia

  • Immediate/Short-term:
    • Hypoxic-Ischemic Encephalopathy (HIE)
    • Renal: Acute Tubular Necrosis (ATN)
    • Cardiac: Myocardial dysfunction, shock
    • Pulmonary: Persistent Pulmonary Hypertension (PPHN), RDS
    • GI: Necrotizing Enterocolitis (NEC)
    • Metabolic: Hypoglycemia, hypocalcemia
  • Long-term Sequelae:
    • Cerebral Palsy (CP)
    • Developmental delay, intellectual disability
    • Epilepsy
    • Visual & hearing impairment

⭐ Sarnat staging of HIE is a key prognostic tool, especially in term infants, correlating with long-term neurodevelopmental outcomes after perinatal asphyxia.

High‑Yield Points - ⚡ Biggest Takeaways

  • Perinatal asphyxia: Intrapartum hypoxia and ischemia causing metabolic acidosis and end-organ damage.
  • Low APGAR scores (especially at 5 minutes) are critical indicators, but not solely diagnostic.
  • Hypoxic-Ischemic Encephalopathy (HIE), graded by Sarnat staging, is the most severe neurological consequence.
  • Therapeutic hypothermia (cooling) for moderate-severe HIE must be initiated within 6 hours of birth.
  • Often leads to multi-organ dysfunction, impacting brain, kidneys, heart, lungs, and liver.
  • Significant long-term sequelae include cerebral palsy, epilepsy, and developmental delays.
  • Prompt resuscitation and supportive care are vital for improved outcomes.

Practice Questions: Perinatal Asphyxia

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Hypothermia is used in all except:

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Flashcards: Perinatal Asphyxia

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Moro reflex in different stages of Hypoxic-ischemic encephalopathy (HIE):Stage I HIE (mild): _____Stage II HIE (moderate): Weak/incompleteStage III HIE (severe): Absent

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Moro reflex in different stages of Hypoxic-ischemic encephalopathy (HIE):Stage I HIE (mild): _____Stage II HIE (moderate): Weak/incompleteStage III HIE (severe): Absent

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