Seizures after initiation of rewarming in cooled infants with hypoxic ischaemic encephalopathy

Background: Seizures after initiation of rewarming from therapeutic hypothermia for neonatal encephalopathy are well recognised but not easy to predict.

Methods: A secondary analysis was performed of NEOLEV2 trial data, a multicentre randomised trial of levetiracetam versus phenobarbital for neonatal seizures. Enrolled infants underwent continuous video EEG (cEEG) monitoring. The trial data were reviewed for 42 infants with seizures during therapeutic hypothermia and 118 infants who received therapeutic hypothermia but had no seizures on cEEG.

Results: Overall, 112 of 160 (70%) had cEEG monitoring continued until rewarming was completed. Of the 42 infants with prior seizures, there were 30 infants with valid cEEG available and seizures occurred following the initiation of rewarming in 8 (26.6%). For the 118 seizure-naive infants, 82 (69.5%) continued cEEG until either rewarming was completed or 90 h of age and none had documented seizures.

Conclusion: Overall, just over a quarter of infants with prior seizures had cEEG evidence of at least one seizure in the 24 h after initiation of rewarming but no seizure-naive infant had cEEG evidence of seizure(s) on rewarming. Critically, by reporting the two groups separately, the data can provide guidance on the duration of EEG monitoring.

Impact: Infants with hypoxic ischaemic encephalopathy who have cEEG evidence of seizures during therapeutic hypothermia have a significant risk of further seizures on rewarming. For infants with hypoxic ischaemic encephalopathy but no cEEG evidence of seizures during therapeutic hypothermia, there is very little risk of de novo seizures. Ongoing work utilising large cohorts may generate EEG criteria that refine estimates of risk for rewarming seizures. Based on current experience, if seizures have occurred during therapeutic hypothermia for hypoxic ischaemic encephalopathy, the EEG monitoring should be continued during rewarming and for 12 h thereafter to minimise the risk of missing an event.