Abstracts

Rationale: Prolonged continuous digital video and electrographic studies (cEEGs) ordered after business hours incur greater resources and costs. This study aimed to identify the incidence of seizure activity in after-hours cEEGs for patients presenting with seizure or seizure-like activity and the factors associated with presence of seizure activity at onset or during the first 12 hours of monitoring.

Methods: This single center retrospective study reviewed cEEGs performed between 6 PM to 6 AM during the period from July 1 to December 31, 2021, for subjects presenting with seizure, status epilepticus, suspicion of nonconvulsive seizure or seizure-like activity. Studies were identified from the EEG Natus database. The cEEGs were reviewed to identify the presence of background abnormality, interictal epileptiform discharges (IEDs), brief ictal rhythmic discharges (BIRDS), periodic patterns, electro clinical seizure (ECSz), electrographic seizure (ESz), electroclinical status epilepticus (ECSE), and electrographic status epilepticus (ESE) at onset and during the first 12 hours of monitoring. The electronic health records were reviewed as regards the timing and indication of the EEG, history of structural brain lesion, metabolic or genetic disorder, seizure disorder, management received prior to EEG (imaging, anti-seizure medications (ASMs)) and whether there was a change of management related to the EEG result.

Results: During the identified period, 123 after-hours cEEGs were ordered, 13 were excluded, and 110 cases were enrolled, 54 females, 55 males, and one identified as other. Five were neonates < 4 weeks, 27 were children < 18 years, and 78 were adults 18- > 80 years old. Forty- five subjects (40.9%) were already intubated and on ASM drip at the time of the study. A total of 33.6% had history of seizure disorder, 60% had a previous abnormal brain imaging study, 30% had history of underlying metabolic or genetic disorder, and 67.3% had brain imaging done before ordering the EEG, which showed a new abnormality in 20.2%. EEG showed background abnormality in 92.5% and IEDs in 29%. Ten subjects (9%) had periodic discharges (Figure 1). At the onset of the study, 7 subjects (6.3%) were having ECSz (2), ESz (1), ECSE (1), and ESE (3). During the initial 12 hours, 16 (16.3%) had ECSz (8), ESz (6), ECSE (1), and ESE (1). Seizure activity occurred during the first 30 minutes of recording in 39.1% and during the first 2 hours in 56.5% (Figure 2). Periodic discharges were statistically significantly more in subjects who had seizure activity (P< 0.001). Only 13.3% of the subjects who were on AMS drip at start of EEG had seizure activity during monitoring.