Anesthesia-Associated Periodic Discharges

Nonconvulsive status epilepticus in patients under intensive care: Should we view epilepsy as a sleep disorder?

Nonconvulsive status epilepticus (NCSE) was initially described in patients with typical and atypical absence status epilepticus (ASE) characterized by states of confusion varying in severity and in focal epilepsies with or without alteration of consciousness. Continuous EEG monitoring of critically ill patients has further refined the classification of NCSE into two main categories: with coma and without coma. Hypnotic, soporific or somniferous epileptic seizures do not exist. On the contrary, patients usually awaken when seizures occur during sleep, and their eyes remain open during ASE. Excessive sleepiness and coma alone are not ictal signs but are observed in the postictal phase of convulsive seizures. On the other hand, excessive sleepiness evolving into coma is a cardinal sign of metabolic/toxic encephalopathies with triphasic waves evolving to burst suppression patterns and ultimately to cerebral inactivity and death. NCSE alone does not directly cause coma. Comas are related to the underlying etiology, patient age and comorbidities, as well as the administration of intravenous sedative drugs to control epileptic seizures. In cases of severe brain injury, NCSE can explain the failure to awaken after the withdrawal of anesthetics and is only an aggravating factor of the neurological condition. In typical ASE, which is characterized by sustained, rhythmic, bilateral, synchronous and unreactive discharges with evolving spatiotemporal patterns (the best example of NCSE), there is no vigilance impairment. This contrasts with metabolic/toxic encephalopathies, which exhibit monomorphic generalized periodic discharges in which patients may become comatose and die. The extended concept of NCSE in comatose patients may lead to an inflated assessment of NCSE, implying a potentially worse prognosis compared to convulsive status epilepticus.

Review of Noninvasive Neuromonitoring Modalities in Children II: EEG, qEEG

Critically ill children with acute neurologic dysfunction are at risk for a variety of complications that can be detected by noninvasive bedside neuromonitoring. Continuous electroencephalography (cEEG) is the most widely available and utilized form of neuromonitoring in the pediatric intensive care unit. In this article, we review the role of cEEG and the emerging role of quantitative EEG (qEEG) in this patient population. cEEG has long been established as the gold standard for detecting seizures in critically ill children and assessing treatment response, and its role in background assessment and neuroprognostication after brain injury is also discussed. We explore the emerging utility of both cEEG and qEEG as biomarkers of degree of cerebral dysfunction after specific injuries and their ability to detect both neurologic deterioration and improvement.

Periodic discharges in veterinary electroencephalography-A visual review

First described in human EEG over 60 years ago, there are very few examples of periodic discharges in the veterinary literature. They are associated with a wide variety of etiologies, both intracranial and systemic, making interpretation challenging. Whether these patterns are indicative of ictal, interictal, or postictal activity is a matter of debate and may vary depending on the clinical features in an individual patient. Periodic discharges have a repeated waveform occurring at nearly regular intervals, with varying morphology of individual discharges from simple sharp waves or slow waves to more complex events. Amplitudes, frequencies, and morphologies of the discharges can fluctuate, occasionally evolving, or resolving over time. This study presents a visual review of several veterinary cases with periodic discharges on EEG similar to those described in human EEG, and discusses the current known pathophysiology of these discharges.

How to evaluate and assess the epileptogenic/seizure potential of periodic discharges along the ictal-interictal continuum?

The ictal–interictal continuum (IIC) is a concept used for those particular EEG patterns that do not meet the strict criteria for status epilepticus but may be associated with neuronal injury. The aim of this article is to review equivocal periodic patterns and to discuss their clinical significance along the IIC. The risk of seizures increases when the frequency of periodic discharges exceeds 2 Hz and when the pattern has features of superimposed rhythmic, sharp, or fast activity (plus modifier). Lateralized periodic discharges (LPDs) are one of the best examples of the IIC. Criteria have been proposed for identifying patterns along the IIC that we called “peri-ictal” LPDs. There is ongoing debate about when to treat patients with these EEG patterns along this spectrum. The term IIC is only an EEG description, and does not in itself reflect a clinical diagnosis, hence management is based on EEG alone. The decision to intensify treatment is based on the combination of EEG, the underlying etiology, the level of consciousness, comorbidities, imaging, and other surrogates of “damage.”