Hypoxic-ischaemic encephalopathy and therapeutic hypothermia — structured clinical encounter

Station brief (candidate)

You are the neonatal registrar. A term infant (39 weeks, birthweight 3400 g) born after an emergency caesarean for placental abruption is admitted to the neonatal unit at 2 hours of age with lethargy, generalised hypotonia, and depressed Moro and suck reflexes. Cord blood pH was 6.88, base deficit 14 mmol/L. Apgar scores were 1, 3, and 5 at 1, 5, and 10 minutes, with ongoing mask ventilation at 10 minutes. The team asks you to assess cooling eligibility, establish the protocol, and outline the supportive neurocare. You have 12 minutes with the team and 5 minutes for examiner discussion. [1]

Information available on request

• Term infant (39 weeks), birthweight 3400 g, emergency caesarean for placental abruption; cord pH 6.88, base deficit 14 mmol/L; Apgar scores 1, 3, 5; ongoing mask ventilation at 10 minutes. [1]
• At 2 hours: lethargic, generalised hypotonia, depressed Moro and suck; no clinical seizures; capillary glucose 3.1 mmol/L; core temperature 36.6 °C. [10]
• aEEG shows a moderately abnormal background with no overt seizure activity; continuous video-EEG has been requested. [4]

Tasks

1. Grade the encephalopathy using the Sarnat criteria and state whether the infant meets the cooling eligibility criteria, justifying from the history and biochemistry. [1]
2. Outline the therapeutic hypothermia protocol in full — target temperature, duration, window for initiation, and rewarming rate — citing the supporting evidence. [4]
3. Describe the supportive neurocare that must be maintained during the 72 hours of cooling, and name three complications of hypothermia and how each is managed. [10]
4. Outline how you would prognosticate after rewarming, naming the imaging modality, its timing, and the injury patterns and what each predicts. [7]

Marking anchors

Must-hit

• Grades the encephalopathy as moderate (Sarnat stage 2): lethargy, hypotonia, depressed primitive reflexes; confirms perinatal asphyxia from the cord pH under 7.0, base deficit at least 12 mmol/L, Apgar 5 at 10 minutes and ongoing resuscitation; states the infant meets cooling eligibility. [1]
• States the cooling protocol: 33.5 to 34.5 °C for 72 hours, started within 6 hours of life, rewarm at 0.5 °C per hour; cites 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. [3] [4] [5]
• Names supportive neurocare: normoglycaemia, normoxia, normocapnia, normotension; seizure treatment to an EEG endpoint with phenobarbital 20 mg/kg IV first-line; coagulopathy and thrombocytopenia monitored and corrected. Complications: sinus bradycardia (benign, not an indication to rewarm), coagulopathy or thrombocytopenia (correct), pulmonary hypertension (screen with pre/post-ductal saturations), subcutaneous fat necrosis (monitor for late hypercalcaemia). [10]

Merit

• Explains the pathophysiological rationale for the 6-hour window: cooling works in the latent phase, before secondary energy failure, by slowing cerebral metabolism and interrupting the excitotoxic and inflammatory cascade. [10]
• For prognostication, names MRI between days 4 and 7 (after rewarming); states that the basal ganglia–thalamus–posterior limb of the internal capsule pattern (profound insult) predicts a high risk of cerebral palsy, while the watershed-zone pattern predicts a cognitive-predominant outcome with a relatively better motor prognosis, and a normal MRI predicts a favourable outcome. [7]

Fail

• Withholds or delays cooling to "complete the work-up" — the 6-hour window closes regardless. [4]
• Actively warms the asphyxiated infant or allows hyperthermia, which extends the brain injury. [10]
• Rewarms rapidly (faster than 0.5 °C per hour), provoking rebound seizures, hypotension and arrhythmia. [4]