Hypoxic-ischaemic encephalopathy and therapeutic hypothermia — branching viva

Station opening

Examiner: "Define hypoxic-ischaemic encephalopathy and explain how it differs from 'birth asphyxia'." [10]

Strong candidate (must-hit)

• Defines HIE as the clinical syndrome of brain dysfunction in the term newborn caused by perinatal hypoxia and ischaemia — a recognisable constellation of altered consciousness, abnormal tone, depressed reflexes, autonomic disturbance and seizures. Explains that "birth asphyxia" describes the insult (the deprivation of oxygen), whereas HIE is the resulting brain syndrome, and that not every asphyxiated infant develops HIE and not every encephalopathic infant was asphyxiated. [10]

Weak candidate

• "It's brain damage from a difficult birth." [10]

Branch A — The eligible term infant

Examiner: "A term infant born after placental abruption with cord pH 6.88 is lethargic, hypotonic and has depressed reflexes at 2 hours of age. Grade the encephalopathy and give your management." [1]

Strong

• Grades the encephalopathy as moderate (Sarnat stage 2): lethargy, hypotonia, depressed primitive reflexes. Confirms perinatal asphyxia from the cord pH under 7.0 and base deficit at least 12 mmol/L. Activates therapeutic hypothermia to 33.5 to 34.5 °C for 72 hours within the 6-hour window, citing the CoolCap (Gluckman 2005), NICHD (Shankaran 2005) and TOBY (Azzopardi 2009) trials and the Jacobs 2013 Cochrane meta-analysis for the reduction in death and major disability. Maintains normoglycaemia, normoxia, normocapnia and normotension; treats seizures to an EEG endpoint; rewarm slowly at 0.5 °C per hour. [1] [4] [5]

Weak

• "Observe for 24 hours and cool if it gets worse." [4]

Branch B — The infant presenting at 10 hours

Examiner: "A term infant with moderate HIE is transferred in at 10 hours of age. The registrar asks whether to cool. What is the evidence?" [8]

Strong

• States that cooling is not standard beyond 6 hours. The Laptook 2017 randomised trial tested cooling started at 6 to 24 hours of life and found no significant reduction in death or moderate-to-severe disability, so the proven benefit is confined to the first 6 hours. Explains the pathophysiology: cooling works in the latent phase, before secondary energy failure is established, and that window closes as the cascade runs. Counsels that individual centres may weigh the equipoise but the evidence does not support routine late cooling. [8]

Weak

• "The 6-hour window is flexible — cool anyway, it can't hurt." [8]

Branch C — The encephalopathic infant with a normal cord gas

Examiner: "A term infant is encephalopathic but the cord pH is 7.25 with a base deficit of 6 mmol/L, there was no sentinel event, and the mother had prolonged rupture of membranes. What is your diagnostic concern?" [10]

Strong

• States that this infant does not meet the biochemical criteria for perinatal asphyxia (pH under 7.0 or base deficit at least 12), so HIE is not the leading diagnosis. The differential is neonatal encephalopathy of another cause — sepsis or meningitis (given prolonged rupture of membranes), metabolic encephalopathy, or stroke. Sends a septic screen and starts antibiotics, checks glucose, ammonia and lactate, and performs a lumbar puncture and MRI. Cooling is reserved for infants who meet the HIE criteria; cooling an HIE mimic is inappropriate. [10]

Weak

• "It's HIE — cool the baby regardless of the gas." [10]

Branch D — The bradycardia during cooling

Examiner: "On day 2 of cooling the heart rate is 92 with a normal blood pressure. The nurse asks whether to rewarm. What do you say?" [4]

Strong

• States that sinus bradycardia is a common, expected and benign effect of a cooled core temperature (33.5 to 34.5 °C) on cardiac conduction. With a normal blood pressure and perfusion it is not an indication to rewarm or to treat as shock. The target temperature is maintained for the full 72 hours, then the infant is rewarmed slowly at 0.5 °C per hour. Rewarming early would forfeit the neuroprotective benefit. [4]

Weak

• "Stop cooling — the bradycardia means the heart is struggling." [4]

Close

Examiner: "Summarise your approach to the term infant with hypoxic-ischaemic encephalopathy in one sentence." [4]

Strong

• "Moderate-to-severe HIE in a term infant — graded by Sarnat staging and confirmed by cord-blood acidosis — is treated with therapeutic hypothermia at 33.5 to 34.5 °C for 72 hours started within 6 hours of life, rewarmed at 0.5 °C per hour, with normoglycaemia, normoxia, normocapnia and normotension maintained throughout and seizures treated to an EEG endpoint; MRI between days 4 and 7 prognosticates, and the death and disability reduction persists into childhood." [4] [5]