New Approaches to Bedside Monitoring in Stroke

Alma Cyrous; Brandon O'Neal; W David Freeman


Expert Rev Neurother. 2012;12(8):915-928. 

In This Article

EEG Monitoring

EEG uses scalp electrodes connected to amplifiers and filters to detect intracranial electrical activity, which is displayed as positive or negative deflections (y-axis) on a line and is recorded versus time (x axis). EEG can be useful in the ICU to detect different brain states, both normal and abnormal. Continuous EEG monitoring (CEEG) in the ICU was problematic until the digital age, which now can save large amounts of EEG recording data on digital computer files rather than large reams of paper. Furthermore, this EEG data can be analyzed in terms of its frequency (Hz), amplitude (microvolts), symmetry (between electrodes, hemispheres and so on) and morphology (e.g., triphasic waves vs normal a patterns) by digital computerized software. This computerized analysis called quantitative EEG (Q-EEG) is starting to emerge as a research and clinical tool to screen for seizures and altered brain states (Figure 4A & 4B).[22]

EEG in the ICU is being increasingly recognized as a means to monitor cerebral function and metabolism. For example, CEEG can help detect seizures that may go unrecognized in comatose or sedated-paralyzed stroke patients, or help titrate anticonvulsant medication.[23–28] Data suggest that earlier detection of seizures and ischemia can lead to earlier intervention, as well as possibly foretell poor prognostic states.[7,29,30] CEEG, however, is faced with numerous challenges in the ICU. First, electrodes often fail to stay on for long periods, which impacts the quality of the recording. Second, there are numerous ICU artifacts such as ventilators, continuous 60 Hz electrical artifact from other devices and monitoring, and sometimes lack of full-channel EEG recording due to lack of space on the patient's head owing to surgical drains and other invasive and noninvasive devices. Real-time interpretation and review of such large amounts of data pose resource issues (interpretation staff reading 365 days a year and at all hours, monitoring, technicians, data storage and network) to most hospitals,[28] which are balanced against the potential benefits of such monitoring.

The principal applications for CEEG in ICU stroke patients are threefold:[27,28,31] first, CEEG can be useful for monitoring and guiding management for patients with brain ischemia from vasospasm (VSP) after subarachnoid hemorrhage (SAH), which can sometimes be hard to detect in mentally altered neurological patients or those with nonspecific, nonlateralizing clinical findings, such as lethargy. Second, CEEG can be useful to monitor for convulsive and nonconvulsive seizures (NCSs), nonconvulsive status epilepticus (NCSE) or guiding anticonvulsant therapy in status epilepticus or NCSE.[32,33] Third, CEEG can help in titrating anticonvulsant drugs, especially in sedated and paralyzed patients, as well as help display trends in brain function and possible prognosis.[31,33]

Specific Stroke EEG Monitoring in SAH Patients

Data support that SAH patients, especially poorer grades (World Federation of Neurosurgeons Scale grade 3–5), have higher incidence of convulsive and NCSs due to low CBF states.[34] These patients have fragile brain metabolism, in which brain parenchymal oxygenation supply and demand are critical. Therefore, earlier seizure detection and intervention helps to balance cerebral delivery of oxygen versus cerebral O2 demand, if treatment leads to earlier cessation of seizure. Seizures increase cerebral metabolic consumption of oxygen and increased cerebral O2 demand in brain-injured SAH patients in which there is disturbed pressure autoregulation. Early detection of seizures – convulsive or nonconvulsive – leading to seizure treatment via CEEG with quantitative or CEEG in poor-grade SAH patients may significantly improve management of these patients. Prophylactic treatment of anticonvulsants in all SAH patients is not recommended and can lead to worse cognitive outcomes.[25] However, SAH patients who seize at onset warrant anticonvulsant therapy and prophylaxis.[23]