Patient demographics, clinical diagnosis, location (ICU or non-ICU), and duration of study were all noted. Continuous EEG findings were defined as (1) normal, (2) containing background rhythm abnormalities without epileptiform abnormality, (3) containing epileptiform abnormality (focal or generalized) without electrographic seizure(s) and (4) containing electrographic seizures (focal or generalized). For this study, on a scalp-derived EEG recording, an electrographic seizure was defined as a paroxysm of entrained rhythmic EEG activity distinctly different from the ambient background EEG activity with some or all of the following characteristics: (1) artifactual origin excluded by appropriate considerations of the EEG pattern (eg, configuration of activity, potential field, no association with physiological sources of artifact [eg, respiratory activity or ballistocardiogram], and no association with extraneous sources of artifact [respirator activity, electrical pumps, and others]); (2) temporospatial evolution with an initial buildup of regularly repetitive sharp wave or rhythmic sinusoidal activity of gradually increasing frequency and amplitude, progressing to a slowing in frequency and a more irregular appearance; (3) transient postictal disorganization and slowing in the same region where the original electrographic seizure arose, (4) of sufficient duration to disrupt normal cortical activities in the involved region, arbitrarily set at 10 seconds, or of sufficient duration to cause clinical impairment (5) usually repetitive in nature and highly stereotypic (Figure 1). An electroclinical seizure was defined as an electrographic seizure with stereotypic and paroxysmal clinical manifestations. When deciding if atypical EEG patterns represent electrographic seizure activity, we included special circumstances in which the designation of a particular EEG pattern as an electrographic seizure arose from the observation of consistent, linked clinical and EEG phenomena. This particularly applies to EEG patterns that may not be particularly striking but are associated with stereotypical clinical manifestations, for example, abrupt electrodecremental responses associated with tonic posturing. This assessment was dependent on bedside clinical assessment or review of videotape accompaniment, which was available in 92 of 300 studies performed. Periodic epileptiform discharges (PEDs) were defined as repetitive monotonous sharp transients occurring throughout the recording, typically every 1 to 3 seconds with some irregularity in the interval between discharges, without entraining into discrete electrographic seizures. PEDs may be unifocal (PLEDs), bifocal or multifocal (BiPEDs), or generalized (GPEDs). We did not categorize PEDs as electrographic seizures but view them as an interictal pattern, often associated with discrete electrographic seizures in the same cEEG recording.