Perinatal Asphyxia

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.

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.
• 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.