(1995). Technical Tips: Non-Collodion Long-Term EEG Monitoring Necessitated by an Allergy to Collodion. American Journal of EEG Technology: Vol. 35, No. 4, pp. 303-304.
The last decade has seen the development and testing of several new drugs to control previously drug-resistant seizure disorders. This brief review introduces technologists to felbamate, gabapentin, and lamotrigine.
.Spectral EEG characteristics are usually reduced after fast Fourier transform (FFT) to the absolute or relative power values for several conventional frequency bands such as alpha, beta, theta, etc. In many cases such analysis is sufficient, but in most cases it does not distinguish between dynamically changing brain states, probably because the concept of an EEG rhythm is too general. Recent data indicate some inconsistencies in traditional frequency bands and a heterogeneity of conventional EEG rhythms. This paper reviews the present state of the art in the field of FFT-based spectral EEG analysis and describes the results and opportunities of higher frequency resolution EEG approach to the understanding of dynamic brain processes.
.Terms used in multivariate statistics are described, with examples of their usage. Included are descriptions of Bonferroni adjustment, Mahalanobis distance, neurometries, multiple correlation, multiple regression, stepwise regression, discriminant function analysis, logistic regression, multivariate analysis of variance, cluster analysis, principal components analysis, factor analysis, and Fourier analysis.
From the very inception of EEG, the distinction between artifactual and cerebral electrical activity has been crucial. Dealing with artifacts effectively is an essential function of the EEG technologist and continues to be challenging. This review includes examples of common artifacts in unfamiliar guises, uncommon artifacts with identifiable characteristics, and some newer artifacts engendered by changing technology.
.Artifacts from electrical or magnetic stimulation can easily overload the amplifiers used in clinical neurophysiology. Most circuits designed to reject stimulus artifact are cumbersome or usable only in special circumstances. I describe an artifact-rejection preamplifier, made from inexpensive parts and based on slew rate limiting, that can interface easily with commercial recording systems. The preamplifier allows successful recording of small and difficult signals such as magnetic sensory potentials and transcallosal cortical responses.
There is an extensive range of EEG patterns associated with drowsiness. The occurrence of burst patterns with a sharp configuration or containing sharp transients was evaluated in 700 consecutive clinical EEGs of adults and children. All recordings included 16 channels of EEG and two channels of eye movements. Recordings included mostly bipolar but also referential montages. Patterns were classified by consensus and regarded as normal variants or of uncertain significance. The main reasons for referral were epilepsy or psychiatric disorders. One or more of 16 different patterns were found in 39% of all subjects. Vertex sharp waves were the most common (n=178) and were initially asymmetrical in 17 cases. Hypnagogic paroxysmal spike-wave bursts were seen in 21/165 children. Sharp transients were also prominent in generalized sharp bursts (n=21), frontocentral sharp bursts (n=3), temporal or vertex sharp waves with alpha (n=6), and beta bursts (n=11). Some drowsiness patterns containing spikes included benign sporadic sleep spikes (n=13), 6/sec spike and wave (n=2), and 14 and 6/sec positive spikes (n=10). Arch-shaped series of waves included the midline theta rhythm (n=19), rhythmical temporal discharge(n=3), and wicket spikes (n=1). Subclinical rhythmical epileptiform discharges of adults (SREDA) were found in two subjects. But-st patterns during drowsiness occur sufficiently often in routine clinical EEG recordings to warrant their careful analysis.
.In the cardiac care unit (CCU), every physician expects to see ECG continuously monitored. ECG monitoring is considered a standard part of patient care in the CCU. For many individual patients, serious cardiac abnormalities do not occur. In these patients, ECG monitoring does provide reassurance that the patient's heart is doing well. In some patients, ECG monitoring provides critical information on developing complications, sometimes allowing early intervention to prevent disastrous, permanent complications before they occur.The neurological application of long-term EEG and evoked potential (EP) monitoring in the neurologic intensive care unit (ICU) has only recently been implemented in a few institutions. Nevertheless, there are many potential uses of EEG and EPs as ICU monitoring tools. Some of these uses include the identification of seizures, the assessment of coma, and the determination of brain death.
Mitochondrial myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like episodes (MELAS) is a syndrome that may be encountered in the acute care setting by EEG technologists. MELAS falls under the general classification of mitochondrial myopathies. It is likely that transmission of the disease is via maternal mitochondrial DNA since a specific point mutation has been identified. There is, however, no definitive proof of the heritability of MELAS and it is nor known how this mutation relates to the clinical symptoms. Specific presenting symptoms and laboratory data can differentiate MELAS from other mitochondrial diseases. This paper provides an outline of MELAS; a case study is discussed to aid technologists in understanding the problems encountered by these patients.
(1995). Electrode Labeling and Braiding. American Journal of EEG Technology: Vol. 35, No. 2, pp. 135-137.
This paper contains technical information and recommendations that may be used to to facilitate intraoperative neurophysiologic monitoring (INM).Electrodes should be attached securely, with low and balanced impedances. Leakage and drying of electrode gel should be averted. Backup electrodes ave advisable. Optimal connecting wire techniques can reduce noise pickup and electrical hazards. Preoperative studies may be used to identify preexisting abnormalities and plan optimum recording techniques.Anesthesia and neuromuscular blockade can interfere with INM; electrical stimuli used for INM can also interfere with the anesthesiologist's assessment of the patient. Baseline data measurements should be repeated when there are substantial changes in the anesthetic regimen or INM recording techniques. The absence of paralysis must be verified prior to any INM procedure that utilizes EMG or motor responses; these responses may also be absent when technical factors prevent stimulating current from reaching the target neural tissue.When rostral SSEPs change, proximal recordings over stimulated nerves can differentiate CNS dysfunction from technical problems and limb ischemia. Stimuli should be larger than the just-suprathreshold values used extraoperatively, in order to provide a safety margin. Both cortical and subcortical components should be recorded when SSEPs are used to monitor the spinal cord.
.Forty consecutive patients who manifested photoparoxysmal responses during the standard electroencephalogram (EEG) were studied prospectively with a standard protocol which involved playing video games, viewing patterns, and watching television. Twelve patients (30%) demonstrated EEG activation while playing video games, five while viewing television, six while viewing patterns, and two while viewing either television or patterns. Two additional patients showed no EEG photosensitivity but had a clinical history of seizures precipitated by video games. The results indicate that patients with paroxysmal EEG responses to stroboscopic light stimulation have a significant risk of activating epileptiform abnormalities by playing video games. However, not all patients with a history of seizures precipitated by video games show EEG light sensitivity in a single testing session.
We report an 85-year-old patient with a history of an old right hemispheric cerebral infarction who was admitted in a coma state. The brain MRI showed an old large right basal ganglia infarction and multiple acute occipital, brainstem, and cerebellar infarctions. The EEG showed nonreactive diffuse rhythmic 9 Hz activity over the left hemisphere and low voltage arrhythmic slowing over the right hemisphere.We postulate that the acute brainstem infarctions are likely the cause of the alpha-coma pattern over the unaffected left hemisphere and the large right basal ganglia infarctions prevented the generation of the alpha activity over the right hemisphere.
Recording an EEG at the patient's bedside can be extremely demanding physically, mentally, and emotionally for the electroneurodiagnostic (END) technologist. Difficult applications, artifact obscured recordings, and limited knowledge concerning the patient's situation produce a very frustrating experience. Recording an interpretable and diagnostically informative bedside EEG requires a teamwork approach. Cooperation between the END technologist, the nurse the physician, the respiratory therapist, and any other patient staff is essential. Electrode application and artifact identification are much easier when the technologist has the assistance and support of the patient staff: Presented below ave brief recommendations for laying the groundwork for technologist and medical staff interaction and cooperation.
.The last decade has seen the development and testing of several new drugs to control previously drug-resistant seizure disorders. This brief review introduces technologists to felbamate, gabapentin, and lamotrigine.
Transcranial Doppler ultrasonography is currently being utilized in many neurodiagnostic and vascular laboratories. Transcranial Doppler ultrasonography, combined with carotid duplex ultrasonography, provides a noninvasive method for assessment of the major arteries in the brain.
Surgical repair of acetabular fractures puts the sciatic nerve at risk for iatrogenic injury. The status of the sciatic nerve can be effectively monitored with somatosensory evoked responses to peroneal and posterior tibial stimulation. The most stable response for monitoring is measured at T12. The unaffected leg can serve as the control with the interlimb amplitude ratio providing a sensitive measure of nerve function. In 88 consecutive cases we monitored, 55 had one or more interventions based on evoked potential findings. Of these 55 patients, 14 had electrophysiologic changes that did not recover to baseline and 41 had full recovery following each intervention. Yet only two patients demonstrated a new sciatic nerve postoperatively.
Mismatched input electrode impedances can lead to noisy EEG and evoked potential recordings even if the electrode impedances are low. This paper presents a quantitative analysis of the phenomenon and illustrative examples.At each amplifier input, the recording electrode impedance and the amplifier's input impedance form a voltage divider. When input electrode impedances are unequal, a common mode signal that is present equally at the two locations on the patient's body appears at different magnitudes at the two (inverting and noninverting) inputs of the amplifier,. thus, part of the common mode signal is amplified as if it were a differential signal. The effective common mode rejection Patio (CMRR) of the amplifier is reduced to a value that can be expressed mathematically as a function of the amplifier's ideal CMRR, its input impedance, and the impedance difference between the two input electrodes.Balanced input electrode impedances are particularly important during intraoperative monitoring, when ambient electrical noise levels are typically high. Recordings between different types of recording electrodes (e.g., between needle and metal cup surface electrodes) are likely to produce impedance mismatches, and thus noisy recordings.
