Electroencephalographic Patterns in Neurocritical Care: Pathologic Contributors or Epiphenomena?
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Electroencephalographic Patterns in Neurocritical Care: Pathologic Contributors or Epiphenomena? Brian Appavu1
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James J. Riviello1
Ó Springer Science+Business Media, LLC 2017
Keywords Electroencephalography Seizures Cortical spreading depolarizations Ischemia Coma Encephalopathy
Introduction Status epilepticus (SE) and repetitive seizures contribute to the development and propagation of brain injury in the intensive care unit (ICU). This has led to the increased utilization of continuous electroencephalographic (cEEG) monitoring to effectively detect and treat seizures. Decades using cEEG recordings have identified several other unique electroencephalographic patterns including periodic discharges (PDs), rhythmic delta activity (RDA), cortical spreading depolarizations (CSDs), and changes in brain activity suggestive of cerebral ischemia. It is unclear whether many of these patterns represent an epiphenomenon of brain injury or physiological phenomena directly contributing to it. Neuroimaging and intracranial multimodality monitoring (MMM) techniques have advanced to allow clinicians to identify physiological changes in cerebral blood flow (CBF), brain tissue oxygenation (PbtO2), cerebral metabolism and intracranial pressure (ICP) and correlate these findings on cEEG. We define and review phenomena observed in the ICU that correlate with unique cEEG patterns, and discuss their
& Brian Appavu [email protected] 1
Division of Child Neurology and Division of Epilepsy, Department of Neurology, Columbia University Medical Center, HP 5, 180 Fort Washington Avenue, New York, NY 10032, USA
known relationship to cerebral metabolism, blood flow and neuronal injury.
Seizures and Status Epilepticus Definition A seizure is defined as ‘‘a transient occurrence of signs and/ or symptoms due to abnormal excessive or synchronous neuronal activity in the brain’’ [1]. SE is a condition resulting from the failure of mechanisms responsible for seizure termination or from the initiation of mechanisms which lead to abnormally prolonged seizures. The newest proposed SE definition has two operational time points that represent either when a seizure is likely to remain prolonged or when neuronal injury and long-term morbidity is imminent [1]. EEG Convulsive seizures are characterized by abnormal electrical activity that directly correlates with clinical manifestations such as tonic–clonic convulsions. Criteria established for non-convulsive seizures include epileptiform discharge complexes greater than 10 s in duration and either greater than 3 Hz in the absence of evolution in frequency, morphology or location, less than 3 Hz and with significant improvement after antiepileptic therapy, or any rhythmic waves greater than 10 s with spatiotemporal evolution [2]. Non-convulsive SE has been characterized by the Salzburg criteria [3], which applies epileptiform discharges greater than 2.5 Hz or rhythmic delta/theta activity exceeding 0.5 Hz and at least one of the following: (a) clinical and EEG
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