Seizure identification in the ICU using quantitative EEG displays

Abstract

Objective: To evaluate the diagnostic accuracy of 2 quantitative EEG display tools, color density spectral array (CDSA) and amplitude-integrated EEG (aEEG), for seizure identification in the intensive care unit (ICU). Methods:A set of 27 continuous EEG recordings performed in pediatric ICU patients was transformed into 8-channel CDSA and aEEG displays. Three neurophysiologists underwent 2 hours of training to identify seizures using these techniques. They were then individually presented with a series of CDSA and aEEG displays, blinded to the raw EEG, and asked to mark any events suspected to be seizures. Their performance was compared to seizures identified on the underlying conventional EEG. Results:The 27 EEG recordings contained 553 discrete seizures over 487 hours. The median sensitivity for seizure identification across all recordings was 83.3% using CDSA and 81.5% using aEEG. However, among individual recordings, the sensitivity ranged from 0% to 100%. Factors reducing the sensitivity included low-amplitude, short, and focal seizures. False-positive rates were generally very low, with misidentified seizures occurring once every 17-20 hours. Conclusions:Both CDSA and aEEG demonstrate acceptable sensitivity and false-positive rates for seizure identification among critically ill children. Accuracy of these tools would likely improve during clinical use, when findings can be correlated in real-time with the underlying raw EEG. In the hands of neurophysiologists, CDSA and aEEG displays represent useful screening tools for seizures during continuous EEG monitoring in the ICU. The suitability of these tools for bedside use by ICU nurses and physicians requires further study. Neurology Nonconvulsive seizures occur in 16%-48% of selected critically ill patients, and may contribute to brain injury if untreated.1-12 Detection of nonconvulsive seizures requires continuous EEG. Increasing awareness about nonconvulsive seizures has led to a growing demand for continuous EEG monitoring in ICUs. To facilitate interpretation of prolonged EEG recordings, several quantitative EEG display tools have been developed to highlight significant electrographic events and provide insight into EEG trends over time.Amplitude-integrated EEG (aEEG) depicts time-compressed and rectified EEG amplitude on a semi-logarithmic scale, and is now commonly employed to monitor cerebral function in neonates.13 While aEEG provides an accurate measure of neonatal EEG background, 14,15 its utility for seizure identification remains a matter of debate. 16 -18 To date, reports on the use of aEEG for seizure identification in pediatric and adult ICUs have been few and descriptive. 19 -22 Color density spectral array (CDSA) applies fast-Fourier transformation (FFT) to convert raw EEG into a time-compressed and color-coded display, also termed a color spectroe-Pub ahead of print on September 22, 2010, at www.neurology.org.

Spectrogram screening of adult EEGs is sensitive and efficient

“…18,20 One study using CSA and amplitude-integrated EEG in 23 pediatric cEEGs (17 with seizures, 10 without) found a sensitivity for seizure detection with CSA of 83.3%. 20 Another study in 8 neonates (26-44 weeks) found that envelope trends enabled experienced users to detect 88% of prolonged seizures, while detection rates for brief or slowly evolving neonatal seizures were only 40% and 20%, 22 suggesting that compressed EEG may be useful in some but not all neonates. In contrast with the present study, in both of these pediatric studies, reviewers were not permitted to correlate compressed data findings with the primary EEG data.…”

“…20,21 These efforts are important because cEEG patterns in the acutely ill are dynamic and require prompt action. However, nonexpert CSA-based screening (without immediate visual confirmation) may yield more false alarms, which might place additional burdens on neurophysiologists charged with following up on such alerts.…”

“…Furthermore, certain EEG features such as voltage asymmetries, abrupt changes such as movement artifacts and seizures, gradual trends in background activity, 18,19 and changes in patterns of recurrent cyclic seizures, may be easily recognized using CSA. 20 Despite increasingly widespread clinical adoption, the empirical performance of CSA-based cEEG review has received little rigorous study. We hypothesized that the time required for expert review of selected segments of raw cEEG data when guided by CSA-based screening is less than that required for conventional review of the entire raw cEEG, without meaningfully compromising sensitivity for seizures or other critical findings.…”

Electrographic seizures in pediatric ICU patients

“…In one study, the median sensitivity for seizure identification was 83% using color density spectral array and 82% using amplitude-integrated EEG, but in individual EEG tracings sensitivity varied from 0% to 100%. 29 Another study applying color density spectral array and envelope trend demonstrated that sensitivity for seizure identification depends on user experience, display size, and inherent seizure characteristics such as duration. 30 We found that 38% of electrographic seizures in children in the PICU lasted less than 1 minute, indicating that a substantial proportion of seizures may be "averaged-out" by highly compressed displays.…”

Computer assisted interpretation of the human EEG

“…Given that most of these patients are in a comatose state, an experi-enced neurointensivist is needed to monitor them on a continuous basis for nonconvulsive seizures (NCS), status epilepticus (NCSE), ischemia, or other abrupt changes with detrimental e ects. For continuous monitoring in an ICU and neonatal critical care environment, EEG is one of the most practical procedures available (Jordan, 1999;Stewart et al, 2010;Abend et al, 2010;Chang and du Plessis, 2012;Riviello, 2013;Sanchez et al, 2013;Young, 2009).…”