Time-Dependent Risk of Seizures in Critically Ill Patients on Continuous EEG

ABSTRACT

OBJECTIVE: Find the optimal Continuous EEG (cEEG) monitoring duration for seizure detection in critically ill patients.

METHODS: We analyzed prospective data from 665 consecutive cEEGs, including clinical factors and time-to-event emergence of EEG findings over 72-hours. Clinical factors were selected using logistic regression. EEG risk factors were selected a priori. Clinical factors were used for baseline (pre-EEG) risk. EEG findings were used for creation of multistate survival model with three states (entry, EEG risk, and seizure). EEG Risk state is defined by emergence of epileptiform patterns.

RESULTS: Clinical variables of greatest predictive value were coma (31% had seizures; OR 1.8; p<0.01) and history of seizures, either remotely or related to acute illness (34% had seizures; OR 3.0; p<0.001). If there were no epileptiform findings on EEG, the risk of seizures within 72-hour was between 9% (no clinical risk factors) and 36% (coma and history of seizures). If epileptiform findings developed the seizure incidence was between 18% (no clinical risk factors) and 64% (coma and history of seizure). In the absence of epileptiform EEG abnormalities, the duration of monitoring needed for seizure risk of <5% was between 0.4hrs (for patients who are not comatose, and no prior seizure) to 16.4hrs (comatose and prior seizure).

INTERPRETATION: The initial risk of seizures on cEEG is dependent on history of prior seizures and presence of coma. The risk of developing seizures on cEEG decays to <5% by 24 hours if no epileptiform EEG abnormalities emerge, independent of initial clinical risk factors. This article is protected by copyright. All rights reserved.

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