Status Epilepticus: cEEG Use

• Status Epilepticus (SE) incidence is around 61 episodes per 100,000 people annually, mortality rate is approximately 20%
• Advances have been made in understanding the causes, EEG correlation, prognosis, and treatment of SE in the past two decades
• Continuous EEG (cEEG) is integral, and guides patient management in the setting of SE
• cEEG is indicated after generalized convulsive status epilepticus (GCSE) to assess for ongoing nonconvulsive status epilepticus (NCSE) in patients with persistent encephalopathy
• cEEG is useful for monitoring SE treatment response, especially with continuous intravenous anesthetics
• cEEG assists in assessing for NCSE in patients who have unexplained coma or altered mental status
• cEEG helps determine if repetitive, involuntary movements represent SE versus nonepileptic events

Definitions of SE

• SE results from the failure of seizure termination mechanisms or the initiation of mechanisms causing abnormally prolonged seizures
• SE is a condition that can have lasting consequences like neuronal death, neuronal injury, and altered neuronal networks depending on seizure type and duration
• The term t₁ refers to the time point at which a seizure should be considered prolonged and unlikely to stop without intervention
• The term t₂ refers to the time point beyond which a risk of long-term consequences exists
• t₁ and t₂ vary for different forms of SE, based mostly on animal data and clinical evidence
• Experts suggest a t₁ of 5 minutes for generalized convulsive status epilepticus (GCSE), and 10 minutes for focal SE with impaired consciousness
• Long-term consequences (t₂) can occur after 30 minutes of GCSE and 60 minutes of focal SE with impaired consciousness
• Task force developed a classification system based on semiology, etiology, EEG correlates, & age

Classification Scheme of SE

• Semiology is the base and differentiated by motor activity and impairment of consciousness
• SE with prominent motor symptoms includes convulsive status epilepticus (CSE)
• Overt CSE is easily diagnosed clinically and often does not need continuous EEG (cEEG)
• SE without prominent motor symptoms includes nonconvulsive status epilepticus (NCSE)
• The previous groups can be further split based on the degree of impaired consciousness
• In the ICU, nonconvulsive status epilepticus (NCSE) often shows as a decreased level of consciousness, like coma
• NCSE occurs with numerous causes so cEEG is needed for definitive diagnosis
• Diagnosing NCSE and distinguishing it from other conditions necessitates cEEG monitoring in the ICU
• Prompt SE identification is critical because outcomes correlate strongly to duration
• The second axis involves SE etiology, and is split in two groups: known/symptomatic and unknown/cryptogenic
• The third axis incorporates EEG correlates with location, name, and morphology of the EEG pattern, and effect of treatment. In convulsive SE, clinical signs are often clear and EEG is often obscured
• The forth axis of age acknowledges electroclinical diagnoses that commonly occur in various age groups

Clinical Semiology

• Seizures in the ICU population are often subtle; only 8% to 32% of patients have a clear clinical correlate
• Critically ill patients can have involuntary movements like clonus, asterixis, shivering, tremor, posturing, or myoclonus that mimic seizure activity
• Repetitive and/or rhythmic movements may be assumed to represent epileptic seizures, leading to unneeded medications that increase potential adverse effects and interactions
• EEG monitoring distinguishes involuntary movements of ictal origin from other movements
• Video analysis alongside EEG is critical to establish if the movements were captured and assessed
• Video aids in diagnosing focal motor seizures that may not correlate on EEG but are suggestive of epileptic seizures based on visual analysis of the semiology

Use of cEEG in the ICU

• Optimal cEEG use should involve conditions that are treatable, reasonably prevalent, and associated with a high risk for further neurological injury, most SE subtypes meet these

• The European Society of Intensive Care Medicine recommends EEG monitoring for patients with CSE who do not return to pre-SE baseline within 60 minutes after seizure medication administration

• For refractory SE patients, EEG should be obtained urgently (within 60 minutes)

• The American Clinical Neurophysiology Society recommends cEEG in patient populations with:

  • Persistently altered mental status post GCSE
  • Altered mental status after acute supratentorial brain injuries
  • Unexplained change or fluctuation in mental status
  • Periodic discharges seen on routine EEG
  • For assessing treatment efficacy in SE patients

• Detecting seizures requires sufficient EEG monitoring duration

• The underlying cause of SE, the treatment effects, postictal encephalopathy, or evolution to NCSE can lead to reduced awareness after clinical seizure cessation

• Refractory cases often need anesthetic agents, requiring cEEG to monitor treatment response and sedation depth

• cEEG determines if ongoing altered consciousness is from persistent electrographic seizures vs treatment effects, primary neurological condition, or postictal state

• Treatment endpoint may vary based on the clinical scenario and treating physician preference, generally falling into cessation of clinical seizures, electrographic seizures resolution, induction of a burst-suppression pattern, & complete activity suppression

• A higher rate of breakthrough seizures appeared with cessation of electrographic seizures, a higher rate of treatment-related complications was documented when targeting full activity suppression

• CEEG optimizes treatment by maximizing seizure control and minimizing adverse effects

Nonconvulsive Status Epilepticus

• NCSE is treatable but hard to detect owing to lack of symptoms
• Limited neurological examination data in ICU patients can be caused by the underlying condition, sedatives, etc
• Several other causes result in decreased level of consciousness in ICU patients whom are also associated with NCSE
• Critically ill patients in a coma with a history of epilepsy, fluctuating consciousness level, acute brain injury, or recent CSE are most at risk for NCSE

Further considerations when using cEEG in the ICU

• Further studies should to assess if detecting/treating electrographic seizures and SE in this population is associated with improved outcomes

Seizures: To treat or not to treat?

• Prolonged seizures, convulsive or nonconvulsive, can lead to neuronal injury, and injury relates to duration of seizure activity
• Studies show that early detection and treatment of NCSE in comatose ICU patients links to decreased mortality
• Further work is needed to determine whether some patient subgroups benefit from treatment more than others

The sequelae of NCS and NCSE support aggressive treatment due:

• Cerebral edema potential
• Ongoing excitotoxicity can increase neuronal injury
• Direct neuronal injury and cognitive decline
• Aggressive arguments contra treatment involve potential, serious, or life-threatening drug reactions/interactions, & prolonged coma duration
• Prolonged coma duration from anesthetics to treat SE, and associated increased length of stay, morbidity, and mortality
• The ICU setting is prone to EEG artifacts, which creates challenges for cEEG use and interpretation
• EEG monitoring involves considerable expense in terms of equipment, personnel, & EEG review time, so availability of equipment and human resources for this service is usually limited
• Appropriate cEEG indications prevent over- or under-utilization
• Quantitative EEG may reduce review time
• CEEG can offer evidence of other causes of encephalopathy that may coexist with SE, such as extension of a vascular process, vasospasm after SAH, or worsening metabolic disturbance
• Momentum exists toward monitoring neurological function with EEG in the ICU, additional studies are needed to determine if the equipment and personnel costs is warranted