Assessing Early Severity of Hypoxic-Ischemic Encephalopathy: The Role of Electroencephalogram Background in Addition to Sarnat Exam

Objective: To assess the relationship between the Sarnat exam, early electroencephalogram (EEG) background, and death or neurodevelopmental impairment (NDI) at age 2 years among neonates with moderate to severe hypoxic-ischemic encephalopathy treated with therapeutic hypothermia.

Study design: Neonates enrolled in the High-dose Erythropoietin for Asphyxia and Encephalopathy trial with EEG (n = 463) or amplitude-integrated electroencephalogram (n = 15) reports available on the first day after birth were included in this cohort study. A Sarnat exam was performed between 1 and 6 hours after birth, and neonates were classified into 3 groups of increasing severity based on the number of severe features (none, 1-2, or 3+). EEG background continuity was extracted from reports and categorized as normal, excessively discontinuous, or severely abnormal. The primary outcome was severe NDI or death at age 2.

Results: Among 478 neonates with hypoxic-ischemic encephalopathy, EEG background continuity was normal in 186 (39%), excessively discontinuous in 171 (36%), and severely abnormal in 121 (25%). For each additional severe feature on the Sarnat exam, the risk of abnormal EEG background increased by 16% (relative risk 1.16 [95% CI 1.09-1.23]). Both the Sarnat exam and EEG background severity were associated with an increased risk of severe NDI or death. After adjusting for Sarnat exam severity, severe EEG background remained associated with severe NDI and death (relative risk 5.7 [95% CI 3.7-8.9]).

Conclusions: The early EEG background provides additional information beyond the Sarnat exam and could be an additional early marker when assessing the severity of HIE.