The early background EEG pattern among neonates whose hypoxic-ischemic encephalopathy (HIE) is treated with therapeutic hypothermia (TH) can help guide how long children need to be monitored with continuous EEG, according to findings presented here at the annual meeting of the Child Neurology Society.
Researchers said the findings point to the potential to greatly shorten the period in which children are monitored at some centers and could help save resources.
Many centers—including the University of Michigan, where the study was conducted—provide continuous EEG monitoring throughout the cooling period of 72 hours and through the re-warming period, for a total of about 84 hours. But many children, according to the retrospective cohort study of 114 neonates, had no seizures and, if they did, most had seizure onset within the first 24 hours of monitoring, said Giulia Benedetti, MD, assistant professor of neurology at Seattle Children's Hospital, who worked on the study while at the University of Michigan.
The study included 114 consecutive neonates who were at least 36 weeks of gestational age and were treated with TH for suspected moderate or severe neonatal HIE. Investigators who were blinded to the children's clinical course reviewed archived clips from the first 24 hours of continuous EEG, and this background was classified as normal or mildly abnormal, moderately abnormal, or markedly abnormal based on an assessment of continuity, amplitude, symmetry, synchrony, epileptiform abnormalities, among other measures.
Seizures were more common among those children with markedly abnormal background EEG: 78 percent had seizures compared with 41 percent among those with moderately abnormal backgrounds and 33 percent with normal or mildly abnormal background EEG (p< .001).
Sixty-seven percent of children with normal or mildly abnormal EEG backgrounds did not have seizures at all, and for the 33 percent who did, seizure onset occurred within the first 24 hours of EEG monitoring.
Only 3.5 percent had seizure onset within 24 to 48 hours, and they all had markedly abnormal early continuous EEG backgrounds.
In three cases, seizure onset came after more than 72 hours. Dr. Benedetti noted that two of these cases were not typical HIE: one child had a markedly abnormal background and was ultimately diagnosed with Ohtahara syndrome—early infantile epileptic encephalopathy—and died from uncontrolled seizures; another had a likely genetic metabolic disorder and died from multisystem organ failure, she said. The third was a more typical case, but after re-warming the child had a cluster of seizures, and at six-month follow-up was developing normally.
The message from those cases, Dr. Benedetti said, is that "if the background is moderately or more severely abnormal, then the [children] are still at risk for the late-onset seizures."
Those in whom seizures began after 72 hours gave telltale signs, she noted. "They all had some kind of clinical correlate at some point with their seizures—like an arm jerk that went along with their seizures," she said.
Dr. Benedetti proposed a tailored approach to the duration of EEG monitoring based on the initial EEG background. If an infant has a normal or mildly abnormal early background and no seizures at 24 hours, that baby can be disconnected from monitoring. Alternatively, if a baby has a moderately or markedly abnormal early background, they should be monitored through cooling and re-warming.
"Continuous EEG monitoring through cooling and re-warming takes a lot of time and uses a significant amount of resources," Dr. Benedetti said. "These data suggest that if, at the 24-hour mark, a baby has a mildly abnormal background and no seizures, it is quite safe to disconnect and there is a very low risk of missing late-onset seizures."
Commenting on the study, Patricia K. Crumrine, MD, FAAN, a pediatric neurologist and professor of pediatrics at the Children's Hospital of Pittsburgh, said that the findings make a persuasive case for using continuous EEG monitoring more sparingly, even if a larger sample size would be better for more completely assessing the safety of discontinuing monitoring after 24 hours for some patients.
She said the findings are strong because of the many parameters that were considered.
"They're talking not only of background, but the synchrony between the two hemispheres, the symmetry between the two hemispheres, and the fact that there aren't EEG seizure discharges that you're seeing (during interictal periods)."
She said infants are monitored through re-warming at her center, but that it might be reasonable to re-think that approach in some cases.