This chapter focuses on the variety of different EEG patterns that can be seen after hypoxic ischemic brain injury, which often produces some of the most severe encephalopathies. Common post–cardiac arrest findings include discontinuity, burst suppression, background voltage attenuation and suppression, lack of EEG reactivity, seizures, myoclonus, and status epilepticus. The prognostic significance of these findings is discussed. Finally, the topic of using EEG as a confirmatory tool in brain death protocols is introduced.

Seizures (epileptic) are manifestations of transient abnormal excessive or synchronized cerebral neuronal activity. Seizures may be provoked (acute conditions) or unprovoked (epilepsy). Seizures are classified as focal or generalized onset based on consistent clinical observation, EEG and imaging findings. Focal onset seizures originate from a single hemisphere while generalized seizures originate from bilateral hemispheres. Focal seizures may be further classified based on impairment of awareness (anytime during seizure) and motor or non-motor activity (at the very onset). Focal seizures without impaired awareness may not have surface EEG abnormalities. Focal seizures may secondarily generalize, these are now called focal to bilateral tonic clonic seizures. Generalized seizures are associated with impaired awareness, hence only motor or non-motor activity at onset is used to classify them. Common generalized motor seizures include generalized tonic clonic seizures (GTCs), tonic, atonic, myoclonic, myoclonic-atonic and epileptic spasms. Common generalized non-motor seizures include typical and atypical absences, myoclonic absences and absences with eyelid myoclonia.