S20. EEG features of nonconvulsive seizures in critically ill patients - Findings from the TRENdS trial

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Introduction There is little data on the EEG features of seizures seen critically ill patients having nonconvulsive seizures (NCS). The Treatment of Recurrent Electrographic Nonconvulsive Seizures (TRENdS) study enrolled 74 such subjects and randomized them to treatment with lacosamide or fosphenytoin. This study evaluates the EEG features of a subset of these subjects. Methods EEG features of 36 of the 74 subjects enrolled in the TRENdS study were analyzed in detail. The extent of spread, onset frequency, offset frequency and morphology of the most common seizure type was assessed. Results In this cohort, the average number of seizures per subject was 35.9 (range 1–339). Seizures were limited to one quadrant (11, 30.6%) or hemispheric (11, 30.6%) in most subjects. Another 14 (38.8%) subjects had seizures that were generalized, bilateral but not generalized or spread to varying extent. Most subjects had seizures with delta frequency onset (18, 50%), while another 9 (25%) had theta frequencies at onset. Another 9 (25%) subjects had seizure onset frequencies in alpha or beta range, or had seizures with varying onset frequencies. At seizure termination, delta frequencies were noted in 29 (80.6%) subjects, while 7 (19.4%) had various other frequencies. The morphology of the seizures was a rhythmic discharge in 17 (47.2%) subjects, recurrent spike or sharp discharges in 5 (13.9%), recurrent spike and wave discharges in 5 (13.9%) and various other morphologies in 9 (25%) others. Conclusion NCS in this cohort of subjects were mostly limited to one hemisphere. The seizure onset frequencies were most often in the delta and theta range, while delta frequencies were noted most often at offset. Rhythmic discharges were the most common morphology.