cEEG in the ICU: An effective tool at the bedside?
EJRC ARTICLE REVIEW
Cerebral activity may be investigated in several ways, one of the simplest being Electroencephalography (EEG). Due to its ease of use at the bedside and sensitivity to changes in both brain structure and function, the use of continuous EEG (cEEG) recording in critically ill patients has increased over the past decade [1, 2]. The aim of this review is to summarise recent results on this topic, focusing on indications, duration of monitoring and technical issues. Firstly it is essential to understand the distinction between non-convulsive status epilepticus (NCSE) and convulsive status epilepticus (CSE). Both are defined as abnormally prolonged seizures lasting more than 5 min, but NCSE is characterised by an absence of prominent motor symptoms. .
Several authors have reported that NCSE is a common finding in critically ill patients, associated with increased mortality and increased risk of poor neurological outcome [4,5,6]. To exclude this condition, a consensus statement from the American Clinical Neurophysiology Society recommends use of cEEG  in five conditions. First, after seizures, if impaired consciousness persists after initial treatment. Evidence is strong for this recommendation. DeLorenzo et al. reported that non-convulsive seizures were observed on cEEG in 48% of cases, and NCSE in 14% of cases . Second, in cases of unexplained alteration of mental status without known acute brain injury, in these cases symptoms may be minor or absent, or include aphasia, confusion, agitation or behavioural abnormalities . Third, when specific EEG patterns are recognised on routine recording: generalised periodic discharges (GPDs), lateralised periodic discharges (LPDs), or BIPDs (bilateral independent periodic discharges). The incidence of seizures ranged from 50% and 88% on routine EEG . In particular, data showed that most of the seizures were non-convulsive. Fourth, in comatose patients after acute brain injury, with incidences of NCSE up to 30% in subarachnoid haemorrhage, head injury, intracerebral haemorrhage, central nervous system infections . Fifth, when neuromuscular blocking drugs (NMBD) are used in high-risk patients.
Therefore, it is evident that cEEG should be initiated as soon as possible when non convulsive seizures are suspected, as traditional 30–60 min EEG recordings identify non-convulsive seizures in only 45–58% of patients in whom seizures are eventually recorded. About 80–95% of patients with non-convulsive seizures can be identified within 24–48 h [9,11].
Further recommendations suggest the use of cEEG to detect ischaemia and for prognostications in critically ill patients. Although many studies have tried to show a specific ischaemic pattern in various conditions [12, 13, 14], the main indication is only for the diagnosis of delayed cerebral ischaemia (DCI) after subarachnoid haemorrhage . In terms of prognosis, A statement from the European Society of Intensive Care Medicine and the European Resuscitation Council suggests that the absence of EEG reactivity to external stimuli and the presence of burst-suppression or status epilepticus at 72 h after cardiac arrest significantly predicts poor outcome, defined as severe neurological disability, persistent vegetative state or death, with a false positive ratio ranging from 0 to 6% .
In conclusion, cEEG is considered one of the most important tools in multiparametric monitoring of neurocritical care patients, providing an interesting challenge for neurointensivists. Further, at this time, evidence that cEEG may improve patient outcome is still lacking. Nevertheless, its limited invasiveness, bedside availability and relatively low costs make cEEG an attractive tool with many potential areas of interest in the multiparametric monitoring of neurocritical care patients.
Article review submitted by NEXT and EJRC Member Temistocle Taccheri, Department of Anaesthesiology and Intensive Care Medicine, A. Gemelli School of Medicine University of Sacred Heart Rome.
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