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🧠 Perinatal Asphyxia - Complete MBBS Notes

Sources: Creasy & Resnik's Maternal-Fetal Medicine | Adams & Victor's Principles of Neurology | Harriet Lane Handbook | Bradley & Daroff's Neurology in Clinical Practice | Park's Preventive Medicine

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1. DEFINITION

• Umbilical artery pH < 7.00

Think of it simply: The baby's "oxygen supply" was cut off around birth, and the brain (and other organs) got starved of oxygen.

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2. INCIDENCE

• Only 10% of brain injuries are related to perinatal/intrapartum events - the rest are prenatal or postnatal.
• Despite widespread fetal monitoring, the incidence of HIE has not decreased significantly.
• Perinatal asphyxia is one of the leading causes of perinatal mortality globally, along with low birth weight and infection. - Park's Preventive Medicine

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3. CAUSES & RISK FACTORS

Antepartum (before labor)

• Severe maternal hypotension
• Placental insufficiency / infarction
• Toxemia of pregnancy (pre-eclampsia/eclampsia)
• Antepartum hemorrhage (abruption, placenta previa)
• Maternal anemia / cardiorespiratory disease
• Intrauterine growth restriction (IUGR)
• Maternal diabetes
• Post-term pregnancy

Intrapartum (during labor and delivery)

• Umbilical cord prolapse / tight cord around neck
• Abruptio placentae
• Uterine rupture
• Prolonged/obstructed labor
• Breech delivery
• Forceps/vacuum delivery causing trauma
• Meconium aspiration

Neonatal (at or after birth)

• Severe respiratory distress syndrome (RDS)
• Congenital heart disease
• Severe anemia (Rh incompatibility)
• Persistent pulmonary hypertension (PPHN)
• Shock / sepsis

Remember: Many cases of CP were once blamed on intrapartum events, but research shows most cases have prenatal origins. - Adams & Victor's Neurology

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4. PATHOPHYSIOLOGY

Step-by-Step Cascade:

Reduced placental/umbilical blood flow
          ↓
    Hypoxemia + Hypercapnia
          ↓
    Switch to anaerobic metabolism
          ↓
    Lactic acid accumulates → Metabolic acidosis
          ↓
    Depletion of ATP (high-energy phosphates)
          ↓
    Cellular energy failure
          ↓
    Release of glutamate (excitotoxic)
    + Influx of intracellular Ca²⁺
    + Lipid peroxidation
    + Nitric oxide accumulation
          ↓
    Cell death (neurons)

Two-Phase Injury:

1. Primary energy failure - During the actual hypoxic event
2. Secondary (reperfusion) injury - Occurs 6-24 hours after birth when blood flow is restored; this is the "secondary energy failure phase." This is the window for treatment (therapeutic hypothermia).

The brain tolerates hypoxia better in the immediate postnatal period than at any other time in life - but only to a point. - Adams & Victor's Neurology

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5. CLINICAL FEATURES

Neonatal Encephalopathy Signs:

• Depressed level of consciousness
• Abnormal muscle tone (hypotonia or hypertonia)
• Abnormal reflexes
• Abnormal respiratory pattern
• Seizures (most important sign - within first 12 hours in severe cases)

Sarnat Staging System (Most Important - Used Clinically)

Harriet Lane Handbook - The Johns Hopkins Hospital

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6. APGAR SCORE - Role in Asphyxia

• Persistently low Apgar at 5 min despite CPR = increased morbidity + mortality
• Combination of: 5-min Apgar ≤5 + need for CPR in delivery room + umbilical arterial pH < 7.00 = 340-fold increased risk of seizures and moderate-to-severe encephalopathy (Perlman and Risser)

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7. MULTIORGAN EFFECTS

Creasy & Resnik's Maternal-Fetal Medicine

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8. DIAGNOSIS

Clinical Criteria for Therapeutic Hypothermia (Eligibility):

1. Gestational age > 35 weeks
2. One or more of the following:
   • Cord gas or blood gas (first hour of life): pH < 7.0 or base deficit > 16
   • If pH 7.01-7.15 or base deficit 10-15.9, then ALSO need:
     • 10-minute Apgar ≤ 5
     • Need for assisted ventilation for ≥ 10 min at birth
3. Evidence of moderate to severe encephalopathy on Sarnat exam

Investigations:

• Blood gas (umbilical artery) - pH, base deficit
• Blood glucose - hypoglycemia common
• Electrolytes - Na, Ca, Mg
• Renal function - BUN, creatinine
• LFTs, coagulation - liver injury, DIC
• CBC - rule out polycythemia, infection
• EEG / amplitude-integrated EEG (aEEG) - monitor seizures, prognostic value
• MRI Brain (gold standard) - Diffusion-weighted MRI detects injury within 24-48 hours
• MR Spectroscopy - detects metabolic changes (lactate, N-acetyl aspartate)
• Cranial ultrasound - for preterm infants and initial screening

DWI-MRI is the gold standard to define extent and timing of brain injury. - Creasy & Resnik

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9. TREATMENT

General Supportive Care (ABC approach):

• Airway - ensure patency, intubate if needed
• Breathing - supplemental O2, mechanical ventilation if respiratory failure
• Circulation - maintain blood pressure, treat shock
• Glucose - correct hypoglycemia (avoid hyperglycemia too)
• Electrolytes - correct Na, Ca, Mg abnormalities
• Seizures - treat with phenobarbital (first-line), phenytoin
• Avoid hyperthermia - even mild fever worsens brain injury

Specific Treatment: Therapeutic Hypothermia (TH) ⭐

Therapeutic hypothermia is now standard of care. Cardiovascular hemodynamics must be monitored carefully during cooling and warming phases. (PMID: 40600298)

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10. PROGNOSIS

Long-term Sequelae:

• Cerebral palsy (spastic, dystonic, or ataxic)
• Epilepsy / seizure disorder
• Cognitive delay / intellectual disability
• Sensory impairments (hearing, vision)
• Learning difficulties
• Behavioral problems

Poor prognostic signs: Seizures + abnormal EEG + abnormal visual/auditory evoked potentials + abnormal MRI

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11. PREVENTION

Antenatal:

• Good antenatal care, early detection of high-risk pregnancies
• Treatment of maternal hypertension, diabetes, anemia
• Fetal monitoring (though EFM has high false-positive rate)
• Antenatal corticosteroids in anticipated preterm delivery (also reduces IVH)
• Maternal transfer to tertiary care center before delivery

Intrapartum:

• Continuous fetal heart rate monitoring
• Timely cesarean section when indicated
• Avoid prolonged labor
• Skilled birth attendants

At delivery:

• Skilled neonatal resuscitation team present
• Prompt NRP (Neonatal Resuscitation Program) - the "ABCD" of resuscitation
• Passive cooling while transferring to NICU (avoid active warming)

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12. KEY POINTS TO REMEMBER (Exam Focus)

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13. QUICK MNEMONICS

• A - Abruptio placentae
• S - Shock (maternal)
• P - Prolapsed cord
• H - Hypertension (uncontrolled)
• Y - Y-leave it too long (prolonged labor)
• X - X-tra trauma (forceps, breech)
• I - Infection
• A - Antepartum hemorrhage

• "Happy → Lazy → Lifeless"
• Mild = Hyperalert (Happy but irritable)
• Moderate = Lethargic (Lazy)
• Severe = Stupor/Coma (Lifeless)

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Recent Evidence Update (2025-2026)

• A 2026 systematic review (PMID: 41760908) highlights that there is still inconsistency in definitions of perinatal asphyxia, HIE, and neonatal encephalopathy across clinical trials - making comparison difficult. Standardized criteria are being developed.
• Post-asphyxia acute kidney injury is now recognized in up to significant proportions of asphyxiated neonates (2026 systematic review, PMID: 42096066) - early nephrology assessment is important.
• Cardiovascular monitoring during therapeutic hypothermia is important as hemodynamic instability is common during both cooling and rewarming phases (PMID: 40600298).

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Secondary Energy Failure Phase - Explained Simply

First, Understand the Three Phases of Brain Injury in Perinatal Asphyxia

PHASE 1          PHASE 2            PHASE 3
Primary      →   Latent Phase   →   Secondary
Energy           (apparent             Energy
Failure          recovery)             Failure

0-30 min        30 min - 6 hrs       6 - 48 hrs
after insult    after insult         after insult

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Phase 1: Primary Energy Failure (The Immediate Injury)

1. Switches from aerobic to anaerobic metabolism (because there's no O₂ for the normal electron transport chain)
2. Anaerobic metabolism is very inefficient - produces only 2 ATP instead of 36 ATP per glucose molecule
3. ATP (the cell's energy currency) rapidly runs out
4. Lactic acid accumulates → metabolic acidosis
5. The Na⁺/K⁺-ATPase pump fails (needs ATP to work) → ionic imbalance
6. Glutamate floods out of neurons into the synapse (massive excitotoxic release)
7. Ca²⁺ rushes INTO the cell through NMDA/AMPA receptors (opened by glutamate)
8. Cell membranes depolarize, neurons start to die by necrosis

This is the "first hit." Many neurons die here directly.

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Phase 2: Latent Phase (The Deceptive Window)

• ATP levels partially recover
• Clinical condition may seem to improve
• EEG activity may transiently normalize

This is the CRUCIAL WINDOW. Therapeutic hypothermia must be started here to prevent Phase 3.

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Phase 3: Secondary Energy Failure (The Delayed, More Damaging Wave)

A. Reperfusion Injury

• Oxygen suddenly arriving in damaged tissue generates reactive oxygen species (ROS) / free radicals
• Free radicals attack cell membranes via lipid peroxidation
• Peak free radical production: ~12 hours post injury
• These remain active for up to a week

B. Persistent Ca²⁺ Overload

• Ca²⁺ that entered during Phase 1 accumulates in mitochondria
• This causes mitochondrial dysfunction - mitochondria can no longer produce ATP efficiently
• Even though O₂ is back, the mitochondria are damaged and can't use it properly → ATP levels fall again ("secondary" energy failure)
• Without ATP, the Na⁺/K⁺ pump fails again → more ionic chaos → more glutamate release → more Ca²⁺ entry (a vicious cycle)

C. Excitotoxicity (Glutamate Storm)

• Glutamate released in Phase 1 keeps acting on NMDA and AMPA receptors
• This drives more Na⁺ and Ca²⁺ influx
• Ca²⁺ activates destructive enzymes: proteases, phospholipases, endonucleases

D. Inflammatory Cascade

• Cytokines like TNF-α and IL-1β are released within minutes of injury
• Neutrophils arrive within 4 hours; peak at 1-3 days
• Microglia activate and proliferate
• Blood-brain barrier becomes permeable (peaks at ~24 hours) → cerebral edema

E. Nitric Oxide Accumulation

• Excess Ca²⁺ activates nitric oxide synthase (NOS)
• Nitric oxide combines with superoxide radicals → peroxynitrite (a highly toxic free radical)
• Peroxynitrite causes lipid peroxidation + DNA damage + protein nitration → apoptosis (programmed cell death)

F. Apoptosis (Programmed Cell Death)

• This is the hallmark of Phase 3 - cells die by apoptosis, not just necrosis
• Mitochondria release cytochrome c → activates caspases → execute cell death program
• Apoptosis is slower and more orderly than necrosis but affects a much larger penumbra of cells (the "at risk" zone around the core of injury)

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Why This Phase Matters Clinically

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How Therapeutic Hypothermia Targets Phase 3

• Slows all biochemical reactions (chemical reactions slow at lower temperatures)
• Reduces glutamate release and excitotoxicity
• Reduces free radical production
• Reduces mitochondrial dysfunction
• Slows apoptosis cascade
• Reduces cerebral metabolic rate → less O₂ demand
• Reduces inflammatory cytokine production

The goal is to arrest Phase 3 before it fully develops. Once secondary energy failure is fully established, the damage cannot be reversed. This is why TH must start within 6 hours. - Creasy & Resnik's Maternal-Fetal Medicine

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Simple Analogy

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Summary Table