Monitoring for seizures in the intensive care unit

Acute symptomatic seizures have been known to occur in critically ill patients for many years. It was not until the widespread use of continuous EEG (cEEG) in the critically ill did we appreciate the incidence of electrographic seizures and status epilepticus in the ICU (Newey and Kinzy, 2018). Many of the seizures that occur are without any apparent clinical signs at the time of the recording. The patients often have convulsive seizures at onset then over the next few hours they lose the ability to have a generalized tonic clonic convulsion. They may then have subtle clinical signs (ictal nystagmus, facial twitching, etc.) or lose any apparent motor response. The end result is that many of the patients lose any clinical signs for their seizures by the time they are in the ICU and their seizures are termed "nonconvulsive." The recognition of seizures in the ICU is important for the effects the seizures have on outcome, particularly in morbidity and mortality and the risk of developing epilepsy after the acute symptomatic event. The use of cEEG in the ICU population has not only highlighted the high incidence of seizure activity but has also been used to assess overall cerebral function with applications in ischemia monitoring and prognostication, and to assess the degree of encephalopathy. This chapter will illustrate the core principles of cEEG monitoring in the critical care population including the incidence of seizures, determining who is at highest risk for seizures, how long patients should be monitored and ICU EEG seizure.