American Clinical Neurophysiology Society Guideline 1: Minimum Technical Requirements for Performing Clinical Electroencephalography PDF

GUIDELINE American Clinical Neurophysiology Society Guideline 1: Minimum Technical Requiremen...

GUIDELINE American Clinical Neurophysiology Society Guideline 1: Minimum Technical Requirements for Performing Clinical Electroencephalography Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC4/OAVpDDa8KKGKV0Ymy+78= on 11/04/2024 Saurabh R. Sinha,* Lucy Sullivan,† Dragos Sabau,‡ Daniel San-Juan,§ Keith E. Dombrowski,k Jonathan J. Halford,¶ Abeer J. Hani,# Frank W. Drislane,** and Mark M. Stecker†† * Department of Neurology, Duke University Medical Center, Neurodiagnostic Center, Veterans Affairs Medical Center, Durham, North Carolina, U.S.A.; †RSC Diagnostic Services, Goodson, Missouri, U.S.A.; ‡Department of Neurology, Indiana University School of Medicine, Indiana University Health Comprehensive Epilepsy Center; §Department of Clinical Neurophysiology, National Institute of Neurology and Neurosurgery, Mexico City, Mexico; kDepartment of Neurology, Duke University Medical Center, Neurodiagnostic Center, Veterans Affairs Medical Center, Durham, North Carolina, U.S.A.; ¶Department of Neurology, Medical University of South Carolina, Charleston, South Carolina, U.S.A.; #Department of Pediatrics With Adjunct Position in Department of Internal medicine, Division of Neurology, Gilbert and Rose-Marie Chagoury School of Medicine, Lebanese American University, Byblos, Lebanon; ** Harvard Medical School, Comprehensive Epilepsy Center, Beth Israel Deaconess Medical Center, Boston, Massachusetts, U.S.A.; and ††Department of Neurosciences, Winthrop University Hospital, Mineola, New York, U.S.A. Key Words: Electroencephalography, EEG, Guideline, Technical Standard. (J Clin Neurophysiol 2016;33: 303–307) A lthough no single best method exists for recording EEGs under all circumstances, the following standards are considered the minimum for the usual clinical recording of Additional channels are often needed for monitoring other physiologic activities and for highlighting activity recorded in specific regions. EEGs in all age groups except the very young (see also Guideline 1.2 Alternating current (AC) wiring should meet the 5: Minimum Technical Standards for Pediatric Electroenceph- Underwriters Laboratories standards required for hospital ser- alography. Sections where modifications are recommended are vice, as per state and local electrical codes. delineated by^for neonates and *for older children). 1.3 In the usual clinical setting, electrical shielding of the This document discusses minimum requirements; follow- patient and equipment is not necessary, and such shielding need ing these requirements alone does not ensure a satisfactory not be installed unless proven necessary. test. Each laboratory should strive for excellence in all aspects 1.4 Ancillary equipment should include a device for of study performance. Recommendations to improve stan- delivering rhythmic, high-intensity flash stimuli to the patient. dardization of procedures and to facilitate interchange of 1.5 Digital EEG equipment should be used for recording. recordings and assessment among laboratories in North Digital equipment provides multiple advantages over paper-based America have also been included. More detail is provided in EEG recording amplifiers, including greater sensitivity, greater recommendations from the International Federation of Clinical reliability, the possibility of postrecording modification of EEG Neurophysiology (IFCN).1 waveform rendering (gain, filters, montage), and more efficient EEG storage. Digital equipment should conform to the recommendations in Guideline 4: Recording Clinical EEG on Digital Media. 1. EQUIPMENT 1.1 ^To display the distribution of EEG activity, it is necessary to record simultaneously from as many regions of the scalp as possible. When too few channels are used, the 2. ELECTRODES chances of interpretive errors increase; conversely, when more 2.1^*Recording electrodes should be free of inherent noise channels are used, the likelihood of such errors decreases. This is and drift. They should not significantly attenuate signals between particularly true for transient activity. 0.5 and 70 Hz. Experimental evidence suggests that silverdsilver Sixteen channels of simultaneous recording are considered chloride or gold disk electrodes held on by collodion are the best, the minimum number required to show the areas producing most but other electrode materials and electrode pastes have been used normal and abnormal EEG patterns. effectively, especially with contemporary amplifiers having high- input impedances. Electrodes must be disinfected with appropriate procedures Address correspondence and reprint requests to Saurabh R. Sinha, MD, PhD, and transmission-based precautions taken after recording from Department of Neurology, Duke University Medical Center, Box 102350, patients with contagious diseases (e.g., viral hepatitis, Creutzfeldt– Durham, NC 27710, U.S.A.; e-mail: [email protected]. Jakob disease, acquired immunodeficiency syndrome).2 Dispos- Copyright Ó 2016 by the American Clinical Neurophysiology Society ISSN: 0736-0258/16/3304-0303 able electrodes may be considered as another option for reducing DOI 10.1097/WNP.0000000000000308 the risk of iatrogenic infections. clinicalneurophys.com Journal of Clinical Neurophysiology Volume 33, Number 4, August 2016 303  S. R. Sinha, et al. Clinical Electroencephalography 2.2 Needle electrodes are not recommended for routine demonstrating noise may still indicate the need to change or clinical use. Beyond considerations of patient discomfort and risk modify that electrode. of injuries to personnel, these electrodes have higher impedances than appropriately applied cup electrodes, resulting in potentially higher levels of noise. Subdermal needle electrodes (SNE) or wire Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 electrodes (SWE) may be used for prolonged recording of EEG in 3. RECORDINGS XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC4/OAVpDDa8KKGKV0Ymy+78= on 11/04/2024 stuporous or comatose patients in situations where application of Montages should be designed in conformity with Guideline 3: cup electrodes is not feasible because of personnel or time A Proposal for Standard Montages to Be Used in Clinical constraints. Although impedances are usually higher, they are Electroencephalography. It is desirable that at least some montages usually well-matched and stable over long recording periods. in all laboratories be uniform to facilitate communication and Manufacturer’s recommendations for insertion, removal, and comparison. Digital systems allow reformatting of montages to disposal of each product are available and should be followed. provide optimal display of activity at the time of interpretation. To 2.3 ^All 21 electrodes and placements recommended by the permit this flexibility, initial recording must be made from IFCN3 should be used. The 10 to 20 System is the only one a referential montage, but the system reference itself cannot easily officially recommended by the IFCN. It is the most commonly be reformatted. For this reason, the digital recording reference used system and should be used universally. The use of the term should be an additional electrode (or combination of electrodes) and “modified 10 to 20 System” is undesirable and misleading when it not one of those in the 10:10 or 10:20 system. An additional means that head measurements have not been made and place- electrode between Cz and Pz is commonly used. The use of linked ments have been estimated. In this case, the term “estimated 10 to ears as a digital recording reference is specifically discouraged. 20 placement” is more appropriate. The term “10 to 10 System” 3.1 ^*The information associated with the record should should be used for the extended combinatorial system described in include, as a minimum, the name and age of the patient, the date Guideline 2: Guidelines for Standard Electrode Position Nomen- of the recording, an identification number, and the name or clature (For neonates, refer to Guideline 5). With some differences initials of the technologist. in naming, electrodes in the 10 to 20 System are included in the 10 Identifications should be made at the time of recording. to 10 System (T3 and T4 in 10–20 system are renamed T7 and T8 Failure to do so may result in errors that have adverse medical in 10–10 system; T5 and T6 in 10–20 system are renamed P7 and and legal consequences. A Basic Data Sheet, associated with P8 in 10–10 system). every record, should include patient name and age, the time and An adequate number of electrodes are essential to ensure that date of the recording, name/initials of the technologist, indication EEG activity having a small area of representation on the scalp is for the EEG (including description of symptoms or events, and recorded and to analyze accurately the distribution of more diffuse their frequency), the time and date of the last seizure/episode (if activity. A smaller number of electrodes may be appropriate for any), the behavioral state of the patient, a list of all medications special circumstances but is not considered comprehensive. the patient has been taking (including premedication given to Occasionally, additional electrodes, placed between or below induce sleep during EEG), presence and location of any skull those representing the standard placements, are needed to record defects, and any relevant additional medical history. Any localized activity better. The 10 to 10 System provides a standard- additions or modifications to standard electrode placements must ized option for selecting additional electrodes. be noted. Additional items that are helpful include handedness, In every case, an isolated ground electrode should be placed time of last meal, and whether patient was sleep-deprived for the and connected to the jackbox as specified by the manufacturer. study. The results of previous neurophysiological testing, The isolated ground does not allow dangerous currents to pass and especially EEGs, should also be included when available. is not a safety hazard as were earth grounds used in early analog 3.2 Appropriate calibrations should be made at the beginning EEG devices. No electrode should ever be connected to the chassis of every EEG recording. This includes at least 10 seconds (or the of the equipment or to the earth ground. In addition, most digital duration needed to reach a stable recording) of a square wave equipment requires one or more system reference electrodes. calibration. For analog systems, a recording with all channels These should be placed as suggested by the manufacturer. connected to the same pair of electrodes should follow at the 2.4^*Interelectrode impedances should be checked as a routine beginning (biologic calibration). At the outset, all channels should prerecording procedure. With modern digital EEG recording be adjusted, if necessary, so that they respond equally and equipment, impedances up to 10 k Ohms are acceptable,4 but correctly to the calibration signal. When doubt as to correct optimal recording still requires impedances that are balanced.5 functioning of any amplifier exists, a repeat calibration run should Unbalanced impedances compromise the ability of an EEG be made. Biologic calibration is not necessary for digital systems. amplifier to reject potentials that are the same at a pair of In addition to the standard square-wave calibration, the biologic electrodes while amplifying those that are different (common calibration may occasionally help in detecting errors in the montage mode rejection). Impedances should also not be below 100 Ohms selection process or in the pen-writing mechanism for analog because this usually indicates a shunt or short circuit, possibly recordings. For this purpose, an anteroposterior (frontooccipital) related to a salt bridge on the scalp. derivation should be used because it can include fast and alpha Electrode impedances should be rechecked during the range patterns as well as eye movement activity in the delta range. recording when any pattern that might be artifactual appears. The calibration is an integral part of every EEG recording. It Still, artifacts may appear even in electrodes with acceptable gives a scaling factor for the interpreter and tests the EEG impedances. Thus, a normal impedance in an electrode machine for sensitivity, high-frequency and low-frequency 304 Journal of Clinical Neurophysiology Volume 33, Number 4, August 2016 clinicalneurophys.com  Clinical Electroencephalography S. R. Sinha, et al. response, noise level, and pen alignment and damping (for area. Interpreters should be aware that some loss of high-frequency analog systems). Calibration voltages must be appropriate for the resolution will otherwise occur, along with the possibility of sensitivities used during the recording. After calibration, visual lower-frequency distortion because of spatial aliasing. review of a 30-second run on the system reference montage A low-frequency filter setting higher than 1 Hz should not without the notch filter is also recommended. be used routinely to attenuate slow-wave artifacts in the record. 3.3 ^*The sensitivity of the EEG equipment for routine Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 Vital information may be lost when pathologic activity in the XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC4/OAVpDDa8KKGKV0Ymy+78= on 11/04/2024 recording should be set in the range of 5 to 10 mV/mm of trace delta range is present. Similarly, a setting lower than 70 Hz for deflection. Sensitivity is defined as the ratio of input voltage to trace the high-frequency filters can distort or attenuate spikes and other deflection. It is expressed in microvolts per millimeter. A commonly pathologic sharp features into unrecognizable forms and can used initial sensitivity is 7 mV/mm, which, for a calibration signal of cause muscle artifact to resemble spikes. Production of a record 50 mV, results in a deflection of 7.1 mm. If the sensitivity is with lost or inaccurate information is poor medical practice. decreased (for example, from 7 to 10 mV/mm), the amplitude of the It must be emphasized, however, that judicious use of the waveform visualized on the EEG also decreases. Conversely, if the low-frequency or high-frequency filtersdwith appropriate anno- sensitivity is increased (e.g., from 7 to 5 mV/mm), the amplitude of tation on the recorddcan emphasize or clarify certain types of a given waveform increases on the EEG. patterns in the record. These filter controls, therefore, should be When the sensitivity is less than 10 mV/mm (e.g., 20 mV/ used selectively and carefully. mm), significant low-amplitude activity may become undetect- 3.5 The 60-Hz (notch) filter can distort or attenuate spikes; it able. If the sensitivity is greater than 5 mV/mm (e.g., 3 mV/mm), therefore should be used only when other measures to reduce 60 normal EEG activity may obscure the tracing and limit Hz interference fail. identification of individual waveforms and frequencies. 3.6 A display of 10 to 20 seconds/page (depending on the With digital systems, this straightforward physical relation- size of the display) should be used for routine recordings ship of sensitivity (millimeter of pen deflection for mV of input (corresponding roughly to a paper speed of 30 mm/second voltage) is lost. Systems can be calibrated for a specific screen, so typically used on paper EEG systems). A display of 15 to 30 that sensitivity retains its physical meaning. When the same data seconds/page is sometimes used for EEG recordings in newborns are redisplayed on a different computer monitor, however, this or in other special situations. relationship may be lost. For this reason, clear scale markers must 3.7^The baseline record should contain at least 20 minutes be shown as part of the display. of technically satisfactory recording. Longer recordings are often During calibration for routine recordings, the recorded more informative. Although the ability to reformat a digital EEG signals should not be distorted but should be large enough to during display allows the entire recording to be viewed in any permit measurement to better than 65% between any of the montage after the recording, displaying the data during acquisi- signals on the different channels. tion in only a single montage is not an acceptable practice. The No matter which sensitivity (within the above limits) is EEG technologist acquiring the recording should view the EEG chosen before the recording, appropriate adjustments should be in at least 3 different montages (including at least one bipolar and made whenever the EEG activity encountered is of too high or one referential montage) during the recording to improve the low amplitude to be recorded properly. ability to identify poor connections in electrodes that may not be 3.4 ^For digital recordings, filtering of the signal occurs at apparent in certain montages and also to allow appreciation of two levels. Analog filters are applied to the incoming signal in subtle abnormalities that require special technical maneuvers the actual amplifier before digitization. These are usually (such as placement of additional electrodes). dependent on the specific amplifier being used and not modifi- The EEG is a short sample of brain activity. Within able by the user, but they do define the ultimate range of reasonable limits, a longer recording time will improve the frequencies being recorded and are important to keep in mind chance of recording an abnormality or abnormalities and of when digitally filtering the signal after collection. demonstrating their variability. Experience in many centers The second level of filtering consists of digital filters that are shows that an absolute minimum of 20 minutes of artifact-free applied before display of the digitized data. These filters are recording (including activation procedures) is necessary to analogous to the filters traditionally used in analog EEG assess baseline EEG activity. Longer recordings are more recording, but unlike in analog recordings, the use of these sensitive to the detection of epileptiform abnormalities and filters in digital recordings does not permanently alter the are encouraged.6,7 The addition of photic stimulation, hyper- recorded data; it only processes the data for display. Proper use ventilation, and especially sleep (which should be recorded of digital filters during data collection is still important. Improper whenever possible) often requires an increase of recording use of digital filters may prevent the technologist from recog- time. nizing relevant EEG abnormalities, artifacts, or changes in 3.8 ^*The recordings should include periods when the eyes electrode impedances that will negatively impact the quality of are open and when they are closed. Proper EEG recordings the recording. For standard recordings, the low-frequency filter require examining the effect of stimuli on the EEG. A should be no higher than 1 Hz (23 dB), corresponding to a time comparison between the eyes-open and eyes-closed condition constant of at least 0.16 second. The high-frequency filter should constitutes one important means for assessment. Some rhythms be no lower than 70 Hz (23 dB). Note, however, that to display can be masked by the alpha activity and are visible only when the frequencies as high as 70 Hz, a computer monitor would need alpha rhythm has been attenuated by eye-opening. Certain forms a horizontal resolution of at least 1,400 pixels in the data display of eye movement may appear to be frontal delta or theta activity, clinicalneurophys.com Journal of Clinical Neurophysiology Volume 33, Number 4, August 2016 305  S. R. Sinha, et al. Clinical Electroencephalography but eye-opening and closing helps in differentiation. Finally, the recording. The stimuli and the patient’s responses or failure to paroxysmal activity may appear only when the eyes are opened respond should be noted in the recording as near as possible to or only when the eyes are closed or at the times these conditions their point of occurrence. change. Thus, failure to record with eye-opening and closing as It is the responsibility of the electroencephalographer to a routine procedure can reduce chances of obtaining potentially recognize the patterns usually associated with different states of Downloaded from http://journals.lww.com/clinicalneurophys by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4 important information. This procedure is so simple that it is consciousness, but observations by the technologist about the XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC4/OAVpDDa8KKGKV0Ymy+78= on 11/04/2024 unjustifiable not to request eye-opening and closure whenever patient’s clinical status can also be of considerable interpretative patient cooperation permits or to manually open and close the value, particularly when discrepancies or unusual correlations eyes when it does not. occur. Photic stimulation should be performed in a room with To facilitate assessing awake background activity, it is dimmed lighting using a lamp placed at least 30 cm from the important for the technologist to ascertain that the patient is patient’s face. Photic stimulation should be performed before maximally alert for at least a portion of the record. hyperventilation or at least 3 minutes after hyperventilation, after 3.11 Special procedures that are of some risk to the patient all hyperventilation-related EEG changes have resolved. should be carried out only in the presence of a qualified Hyperventilation should be used routinely unless medical physician, only in an environment with adequate resuscitation or other justifiable reasons (e.g., a recent intracranial hemor- equipment, and with the informed consent of the patient or rhage, significant cardiopulmonary disease, sickle cell disease responsible relative or legal guardian. or trait, or patient inability or unwillingness to cooperate) 3.12 In most situations, the EEG is interpreted by a neuro- contraindicate it. It should be performed for a minimum of physiologist after the recording is completed. This should be 3 minutes, with continued recording for at least 1 minute after done in a timely fashion. The technologist should notify the cessation of overbreathing. At times, hyperventilation must be interpreting physician and supervisor for critical results. These performed for a longer period to obtain adequate activation of include the presence of electrographic or clinical seizures during the EEG. To evaluate the effects of this activation technique, at the record, as well as other significant clinical events. least 1 minute of recording with the same montage should be 3.13 EEGs for the evaluation of cessation of cerebral obtained before overbreathing begins. The record should function (“cerebral death”) require special procedures and contain an assessment of the quality of patient effort during extraordinary precautions (see Guideline 6: Minimum Technical hyperventilation. Standards for EEG Recording in Suspected Cerebral Death). A single-channel electrocardiogram (ECG) should be 3.14 Although not an absolute requirement, simultaneous included on one EEG channel. It is often helpful if spikes and video recording with the EEG is a useful adjunct and is now sharp waves, or pulse or ECG artifact, are in question. routine in many laboratories. This may be useful for interpreting Photic stimulation and hyperventilation are provocative clinical events as well as identifying artifacts. The use of video maneuvers intended to elicit epileptiform discharges, and does not reduce the importance of having an attentive technol- potentially seizures, in susceptible patients. Patients and care- ogist. If video is recorded, institutional policies should be givers should be informed of this possibility in advance. followed regarding the need for consent. Storage and use of 3.9 ^*Sleep recordings should be performed whenever the video for any nonclinical purpose (e.g., educational) should possible, but not to the exclusion of the waking record. also be consistent with institutional policies. Considerable additional information can be obtained by record- 3.15 EEG data should be stored/archived in accordance with ing during drowsiness and sleep, especially about epileptiform institutional and state policies for record retention. Because EEG discharges.8,9 Some laboratories use sleep recording routinely. interpretation has some subjectivity, recordings should be made Sleep recording is usually essential for patients with suspected or available when requested by outside physicians. known seizure disorders. Sleep deprivation may be used to increase the yield of EEGs.10,11 In patients with epilepsy, sleep deprivation increases the frequency of detection of epileptiform discharges, even DISCLAIMER during wakefulness. This statement is provided as an educational service of the 3.10^*The patient’s level of consciousness (awake, drowsy, American Clinical Neurophysiology Society (ACNS). It is based sleeping, or comatose), and any change thereof, should be noted on an assessment of current scientific and clinical information. It by the technologist on the EEG recording. Any commands or is not intended to include all possible proper methods of care for signals to the patient, and any movement or clinical seizure a particular problem or all legitimate criteria for choosing to use activity or absence thereof, should also be noted on the a specific procedure. Neither is it intended to exclude any recording. Careful observation of the patient with frequent reasonable alternative methodologies. American Clinical Neuro- notations is often essential, particularly when unusual wave- physiology Society recognizes that specific patient care decisions forms are observed in the tracing. Abbreviations used should be are the prerogative of the patient and the physician caring for the standardized, with their definitions readily available to the patient based on all of the circumstances involved. The clinical reader. context section is made available to place the evidence-based In stuporous or comatose patients and those showing guidelines into perspective with current practice habits and invariant EEG patterns of any kind, visual, auditory, and challenges. Formal practice recommendations are not intended somatosensory stimuli should be applied systematically during to replace clinical judgment. 306 Journal of Clinical Neurophysiology Volume 33, Number 4, August 2016 clinicalneurophys.com  Clinical Electroencephalography S. R. Sinha, et al. 6. Losey TE, Uber-Zak L. Time to first interictal epileptiform discharge in REFERENCES extended recording EEGs. J Clin Neurophysiol 2008;25:1–4. 7. Modur PN, Rigdon B. Diagnostic yield of sequential routine EEG and 1. 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