Utility and rationale for continuous EEG monitoring: a primer for the general intensivist

Abstract

This review offers a comprehensive guide for general intensivists on the utility of continuous EEG (cEEG) monitoring for critically ill patients. Beyond the primary role of EEG in detecting seizures, this review explores its utility in neuroprognostication, monitoring neurological deterioration, assessing treatment responses, and aiding rehabilitation in patients with encephalopathy, coma, or other consciousness disorders. Most seizures and status epilepticus (SE) events in the intensive care unit (ICU) setting are nonconvulsive or subtle, making cEEG essential for identifying these otherwise silent events. Imaging and invasive approaches can add to the diagnosis of seizures for specific populations, given that scalp electrodes may fail to identify seizures that may be detected by depth electrodes or electroradiologic findings. When cEEG identifies SE, the risk of secondary neuronal injury related to the time-intensity "burden" often prompts treatment with anti-seizure medications. Similarly, treatment may be administered for seizure-spectrum activity, such as periodic discharges or lateralized rhythmic delta slowing on the ictal-interictal continuum (IIC), even when frank seizures are not evident on the scalp. In this setting, cEEG is utilized empirically to monitor treatment response. Separately, cEEG has other versatile uses for neurotelemetry, including identifying the level of sedation or consciousness. Specific conditions such as sepsis, traumatic brain injury, subarachnoid hemorrhage, and cardiac arrest may each be associated with a unique application of cEEG; for example, predicting impending events of delayed cerebral ischemia, a feared complication in the first two weeks after subarachnoid hemorrhage. After brief training, non-neurophysiologists can learn to interpret quantitative EEG trends that summarize elements of EEG activity, enhancing clinical responsiveness in collaboration with clinical neurophysiologists. Intensivists and other healthcare professionals also play crucial roles in facilitating timely cEEG setup, preventing electrode-related skin injuries, and maintaining patient mobility during monitoring.

Keywords: Continuous EEG; Delirium; Encephalopathy; Ictal-interictal continuum; Intensivist; Intracranial EEG; Neuroprognostication; Periodic discharges; Seizures; Status epilepticus; Traumatic brain injury.

Fig. 1

Sample EEGs of various commonly seen rhythmic and periodic patterns. A Generalized periodic discharges (GPDs) at roughly 1 Hz Frequency. B Generalized rhythmic delta activity + Sharp Activity (GRDA + S) at roughly 2 Hz Frequency. C Lateralized periodic discharges (LPDs) Right Frontal predominant at roughly 0.5 Hz Frequency. D Lateralized rhythmic delta activity (LRDA), Left Frontal predominant at 1 Hz. Frequency. E bilateral occipital independent periodic discharges at bilateral occipital lobes. 0.5–1 Hz Frequency. F brief potentially ictal rhythmic discharges (BIRDs) fronto-central predominant

Fig. 2

Rhythmic and Periodic Patterns and Seizure Risk Associated with Pattern Frequency. Illustration of variable seizure risk associated with commonly seen rhythmic and periodic patterns on continuous EEG monitoring. The X-axis represents the patterns' frequency, and the Y-axis represents the associated relative seizure risk. Generalized rhythmic delta activity (GRDA), Generalized periodic discharges (GPD), Lateralized rhythmic delta activity (LRDA), Lateralized periodic discharges (LPD), + (plus features [sharp and/or fast activity]). Adapted from Rodriguez Ruiz A, Vlachy J, Lee JW, et al. Association of Periodic and Rhythmic Electroencephalographic Patterns With Seizures in Critically Ill Patients. JAMA Neurol. 2017;74(2):181–188. https://doi.org/10.1001/jamaneurol.2016.4990

Fig. 3.

2HELPS2B score. A point system designed to stratify inpatient seizure risk based on 5 electrographic features and one clinical factor (history of seizures). The score was validated to predict seizure risk and guide physicians in determining the minimum required EEG duration. Abbreviations: BIPD, bilateral independent periodic discharge; LPD, lateralized periodic discharge; LRDA, lateralized rhythmic delta activity

Fig. 4

Rapid Response mobile EEGs—A: Zeto EEG monitoring device that can be worn like a bike helmet and adjusted according to head size. It has 19 electrodes with A1/A2 reference electrodes and 10–20 system complaints. B: Ceribell EEG headband that any healthcare provider can set up rapidly with the pocket-sized Ceribell EEG recorder that provides clinical quality EEG of 10 channel electrodes and on-device EEG. C: EMOTIV EPOC^x EEG headset is a 14-channel EEG with a 9-axis motion sensor that can detect head movements. It uses Bluetooth technology to wirelessly transmit data to a computer or mobile device to obtain real-time monitoring of brain activity. D: VitalEEG™ Wireless EEG Headset is a low channel count that can be rapidly deployed by any ER or ICU nurse and remotely monitored by an EEG technologist or physician. Adapted from: https://zeto-inc.com/device/, https://ceribell.com/, https://www.emotiv.com/epoc-x/, https://us.nihonkohden.com/products/vitaleeg-wireless-eeg-headset/

Fig. 5

Cortical Myoclonus After Cardiac Arrest: A Elmer Pattern 1. Epoch captured on longitudinal bipolar montage with high-pass filter at 1 Hz, low-pass filter at 70 Hz, paper speed of 30 mm/second, sensitivity at 7 uV/mm, and notch filter off. A 65-year-old man with hypoxic-ischemic brain injury following an asystolic cardiac arrest with prolonged time to return of spontaneous circulation. Static periodic highly epileptiform and identical bursts consisting of high amplitude polyspikes captured in lockstep with whole body myoclonus (not shown). B Elmer Pattern 2. Epoch captured on longitudinal bipolar montage with high-pass filter at 1 Hz, low-pass filter at 70 Hz, paper speed of 30 mm/second, sensitivity at 7 uV/mm, and notch filter off. A 59-year-old woman with hypoxic-ischemic brain injury following a pulseless electrical activity cardiac arrest with prolonged time to return of spontaneous circulation. Fluctuating midline predominant periodic spikes in lockstep with subtle myoclonus of the face and hands (not shown)

Fig. 6

Consensus statement and recommendations for a generalized stimulus protocol for EEG reactivity testing and definition of EEG reactivity in patients after cardiac arrest. The text in black represents the statements derived from the consensus which was defined as ≥ 75% agreement. Text in red represent the set of recommendations that were defined as having a 66–75% agreement. Stimulus induced rhythmic or periodic discharges (SIRPIDs). Adapted from Admiraal MM, van Rootselaar AF, Horn J. International consensus on EEG reactivity testing after cardiac arrest: Towards standardization. Resuscitation. 2018 Oct;131:36–41. https://doi.org/10.1016/j.resuscitation.2018.07.025. Epub 2018 Jul 26. PMID: 30056156