Background Therapeutic hypothermia (TH) is standard of care in newborns with hypoxic-ischemic encephalopathy (HIE). Although the predictive value of amplitude-integrated EEG (aEEG) after HIE has been studied, the predictive value of aEEG during TH remains to be established.

Aim To study aEEG characteristics and timing of recovery of neurobehavior in a newborn piglet model of HIE following TH.

Methods Newborn piglets (N=14) were subjected to 30 min hypoxia-ischemia and survived to 72h. Animals were randomly assigned to hypothermia (N=8) or normothermia for 24h after hypoxia-ischemia (N=6). aEEG was continuously recorded until ~40h post-insult and at 48 and 72h post-insult. Background pattern aEEG and presence of seizures were analysed. Neurobehavior was scored from 40 until 72h post-insult.

Results In hypothermic piglets aEEG background pattern recovered to continuous low voltage (CLV) within 2h post-insult until 36h post-insult. Normothermic piglets recovered within 2h post-insult to continuous normal voltage (CNV) until 36h, where there was a decrease in background pattern to CLV. aEEG recovered to CNV in both groups by 72h post-insult. Seizures were recorded in 50% of hypothermic piglets c.f. 83% in normothermic piglets. At 48h post insult both groups showed a maximum of epileptic activity. The neurobehavioral score in the normothermic piglets showed an earlier return to baseline compared to the hypothermic piglets.

Conclusions Electrographic seizure burden was decreased following TH. aEEG background pattern and neurobehaviour score recovered earlier in normothermic piglets, suggesting that in the clinical situation conclusions based on aEEG and neurological examination should not be performed too early.