Continuous EEG monitoring in the neuroscience intensive care unit and emergency department

Localizing acute stroke-related EEG changes: assessing the effects of spatial undersampling

Because of its sensitivity to metabolic and ionic disturbances related to ischemia, the EEG can be a potentially useful tool for acute stroke detection and for monitoring affected tissue. However, the clinical use of the EEG in detecting stroke is determined in part by how accurately the spatial information is characterized. The purpose of the current study was to determine the effects of spatial undersampling on the distribution and interpretation of the stroke-related topographic EEG. Using a 128-channel sensor montage, EEG was recorded from six stroke patients acutely (between 8 and 36 hours) after symptom onset. The EEG was submitted to a spectral analysis and was compared with patient symptoms and MRI and computed tomographic findings. To determine loss of spatial and clinical information resulting from spatial undersampling, the average-referenced data from the original 128-channel recording montage were subsampled into 64-, 32-, and 19-channel arrays. Furthermore, the analytical findings were compared with a board-certified electroencephalographer's review of the raw EEG using a conventional clinical montage. As predicted, the results showed that accurate description of stroke-related topographic EEG changes is dependent on adequate spatial sampling density. Accurate description of the spatial distribution of the stroke-related EEG was achieved only with the 64- and 128-channel EEG. As the recording density decreases to 32 channels, the distribution of the scalp EEG spectra is distorted, potentially resulting in mislocalization of the affected region. Results of the clinical review by an expert electroencephalographer corroborated the quantitative analyses, and the results also demonstrated the shortcomings of the conventional 10-20 recording density for capturing focal EEG abnormalities in several cases. The EEG provides useful information about the localization of acute cerebral ischemia, but recording densities of 64 channels or higher are required for accurate spatial characterization of focal stroke-related EEG changes.

Electrophysiologic monitoring in neurointensive care

Cumulative evidence of potential benefits of electroencephalography (EEG) and evoked potentials in the management of patients with acute cerebral damage has been confirmed. Continuous EEG monitoring is the best method for detecting nonconvulsive seizures and is strongly recommended for the treatment of status epilepticus. Continuously displayed, validated quantitative EEG may facilitate early detection of secondary cerebral insults and may play a decision-making role in the management of patients with head injury, stroke, or subarachnoid hemorrhage. Long-latency auditory evoked potentials and cognitive components constitute a new field of interest for the progress of comatose patients. Motor evoked potentials may become clinically important both in acutely injured and elective postoperative patients. In the neurointensive care units adequate techniques can be selected to answer targeted clinical questions. The efficacy can be improved by implementing educational projects based on ad hoc training of nurses and neurointensive care specialists.

Seizures in the adult intensive care unit

Seizures are a common occurrence in the intensive care unit (ICU). The presentation of seizures is usually as focal or generalized motor convulsions, but other seizure types may occur. Etiologies of the seizures are typically secondary either to primary neurologic pathology or a consequence of critical illness and clinical management. Particularly important as precipitants of seizures are hypoxia/ischemia, drug toxicity, and metabolic abnormalities. It is important to properly diagnose the seizure type and its cause to ensure appropriate therapy. Most seizures occur singly, and recurrence is usually prevented with initiation of anticonvulsant therapy. However, status epilepticus may develop, which requires emergent treatment before irreversible brain injury occurs. Treatment with anticonvulsants is not without untoward risks, however, and primary toxicities of these agents is reviewed. After traumatic head injury, brain surgery, or cerebrovascular accidents, many patients are at risk for seizures. Current data on the benefits of prophylactic therapy for such patients is also reviewed.

[Diagnosis of status epilepticus by continuous EEG monitoring in a neurointensive care unit]

Continuous EEG monitoring use has documented a surprisingly high incidence of convulsive and non-convulsive status epilepticus in patients with acute brain injuries. Seizures are the cause of secondary insult. Many problems may be encountered during EEG recording, such as electrical interferences and artefacts arising from the patient. To minimise these problems, we suggest the following: train the bedside nurse, make a library of the artefacts, have the EEG technologist check electrodes and establish low impedance, have the electroencephalographer examine the EEG, correlate the activity and movements of the patient. In the diagnosis and the management of convulsive and non-convulsive status epilepticus, the value of continuous EEG monitoring appears to be established.

Periodic lateralized epileptiform discharges after evacuation of subdural hematomas

Periodic lateralized epileptiform discharges (PLEDs) have been recorded in some patients with subdural hematomas. In most of the patients, PLEDs occurred before the hematoma was evacuated. Five patients (three men and two women) who ranged in age from 57 to 88 years had PLEDs and seizures after evacuation of a subdural hematoma. The PLEDs occurred 1 to 9 days after evacuation and were associated with clinical seizures and altered consciousness. After treatment with anticonvulsant agents, the PLEDs and seizures resolved. The presence of PLEDs should be considered in patients who, after evacuation of a subdural hematoma, have altered consciousness, lateralized neurologic findings, or seizurelike activity (or a combination of these features).

Application of technology in the treatment of traumatic brain injury

The goal of care of the traumatic brain-injured patient is to prevent secondary injury. Technology gives the caregivers information as to the cause and severity of injury and can guide appropriate management of the patient. Use of multimodality monitoring increases the complexity of care but may allow for better targeted therapy. This article will discuss the current state of technology, the physiology and pathophysiology that it assesses, the normal and abnormal values obtained, and how care will be impacted.

Intensive care unit management of the stroke patient

Although the majority of patients with acute stroke do not require intensive care, it is important to recognize when admission to an intensive care unit (ICU) is warranted. Patients undergoing thrombolytic therapy, those with brainstem infarcts referable to the basilar artery, those with large space occupying hemispheric infarcts, and those with fluctuating neurological examinations should be admitted to the ICU for monitoring and treatment.

Nonconvulsive status epilepticus in acute brain injury

Whether or not nonconvulsive status epilepticus produces permanent brain damage is a source of controversy. Contributing to the controversy is the lack of clarity for classifying the clinical and electrographic phenomena that constitute nonconvulsive status epilepticus. Nonconvulsive status epilepticus commonly occurs in the context of an acute brain injury. For example, it commonly persists in generalized convulsive status epilepticus after convulsive activity has stopped, and it is not uncommonly associated with acute cerebral ischemia. Its clinical characteristics are ambiguous, subtle, and nonspecific making the diagnosis difficult. In the absence of EEG testing, it is likely to be missed or delayed. When acute brain injury and nonconvulsive status epilepticus occur concurrently, the severity of acute brain injury has traditionally been accepted as determining patient outcome. However, increasing evidence suggests that the two conditions are synergistically detrimental and increase brain injury. Guidelines remain to be established for the intensity and duration of anticonvulsant therapy in these patients. Evidence suggests that, in the absence of extreme and irreversible acute brain injury, early intensive intervention is necessary to improve the otherwise poor outcome of these patients.