Emergent EEG in the emergency department in patients with altered mental states.

OBJECTIVE: To evaluate whether EEG performed within 30 min of referral by an ED physician helps establish diagnosis and/or changes management and in which clinical setting.
METHODS: Single-center prospective cohort intervention study 1 day/week, of sequentially referred adult patients with clinical seizures or altered mental status (AMS). Standard EEGs were performed by an EEG technician using a commercially available cap, interpreted by an epileptologist, immediately reported to the ED physician and a utility survey completed. Quality and interpretation of 20 min EEGs was compared to pre-specified 5 min segments of each EEG using the kappa coefficient.
RESULTS: Over 1 year, 82 patients underwent ED EEG. Tonic clonic seizure activity had occurred in 33%. Mean time for EEG setup was 13.1 ± 6.2 min. EEG assisted the diagnosis in 51%, changed ED management in 4% and would be ordered again if EEG was available in 46%. Positive utility of EEG was significantly associated with toxicologic, psychiatric and endocrine/metabolic causes of AMS vs. other causes (p<0.001) and sudden onset AMS (p=0.007). Independent predictors of whether ED EEG would be ordered if available were witnessed seizures (p=0.01), no prior head trauma (p=0.001) and survey respondent being a physician assistant (vs. MD) (p=0.02). The 5 (vs. 20) min EEG presented good agreement on waveform shape/amplitude (kappa=0.78), artifact (kappa=0.75) and interpretation categories (all kappa levels ≥ 0.70).
CONCLUSIONS: Rapid availability of standard full-montage EEG in the ED is feasible and helps establish a diagnosis in about half of AMS patients, but rarely changes management. An abbreviated 5 min full-montage EEG presents adequate reliability which may improve use in the ED. SIGNIFICANCE: Specific presentations of AMS offer the best diagnostic benefit for EEG in the ED.