Continuous EEG monitoring in aneurysmal subarachnoid hemorrhage: a systematic review

Continuous EEG (cEEG) may allow monitoring of patients with aneurysmal subarachnoid hemorrhage (SAH) for delayed cerebral ischemia (DCI) and seizures, including non-convulsive seizures (NCSz), and non-convulsive status epilepticus (NCSE). We aimed to evaluate: (a) the diagnostic accuracy of cEEG as a confirmatory test, (b) the prognostic value of EEG patterns suggestive of seizures and DCI, and (c) the effectiveness of intensified neuromonitoring using cEEG in terms of improved clinical outcome following SAH.

A systematic review was performed with eligible studies selected from multiple indexing databases through June 2014. The methodological quality of these studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2.

Eighteen studies were identified, including cEEG data from 481 patients with aneurysmal SAH. NCSz were diagnosed in 7-18 % of patients; NCSE in 3-13 %. NCSE was associated with increased age (mean age 68 years) and mortality (82-100 %) compared to the entire patient population (53.9 years; mortality 13 %; p values <0.05). DCI was diagnosed in 20-46 % of patients. Quantitative EEG patterns suggestive of DCI included decreased alpha/delta ratio, relative alpha variability, and total power. All studies were subject to a high risk of bias concerning patient selection and cEEG methodology.

cEEG monitoring following SAH detects an increased number of subclinical seizures and may predict DCI many hours in advance. NCSE is associated with high mortality and morbidity, whereas for DCI identified by cEEG this association is less clear. Prospective randomized controlled multicenter trials are needed to evaluate the benefits (or risks) of intensified treatment of seizures and DCI following SAH.