The value of an EEG depends largely upon its technical quality, which depends on the cooperation of the patient and the experience of the technologist.
Sixteen-channel EEG recordings permit easier and more reliable evaluation of both focal and generalized phenomena than do EEGs with fewer channels. For clarity of presentation, some of the illustrations in this atlas are 8-channel selections from 16-channel recordings. Both digital- and analog-recorded illustrations are included. The electrocardiogram (ECG/EKG) channel is included only when relevant.
A hospital EEG laboratory should be situated in an area accessible to both outpatients and inpatients, allowing transportation of small patients as well as larger ones into the laboratory. Portable EEGs are necessary for inpatients located in intensive care areas and for those with unstable conditions who cannot leave the floor. Physicians should be available for medical emergencies.
Each recording room should be equipped with an EEG machine, sink, small supply table, stretcher, and rocking chair as well as a straight-back chair with arms. There should be ample room for a wheelchair or an extra stretcher for those patients who arrive on such and cannot transfer with ease. For safety, a telephone is a necessity. A small desk is ideal and wall shelving nicely stores the required linens. A child-themed décor with brightly colored pictures will calm a nervous child. Soft instrumental music in conjunction with dimmed lighting will add to a more soothing environment, thus promoting sleep in patients of all ages. A well-organized, clean recording room will inspire confidence in the technologist among parents and patients alike.
All equipment required by the technologist should be accessible and within arm's reach. Cooperation will be better maintained if there are no breaks in the continuity of the procedure. Placement of the EEG machine should allow the technologist a full view of the patient and provide easy access should a seizure occur or other aid be required.
To allow adequate time, a maximum of five patients within a 7.5 hour day per technologist should be scheduled. Ideally, in a large hospital where many EEGs are requested, three time slots would be appropriate for outpatients, leaving two time slots available for inpatient and/or emergent requests. If no such patients are in need of EEGs, then outpatients could be brought forward from future dates.
For children 6 months to 4 years of age, early afternoon appointments are desirable, since the child will have been fed and may need a nap, permitting an EEG containing both wakefulness and sleep. Remind parents ahead of time of the importance of sleep during the EEG.
Infants less than 6 months of age can be booked at any time, since sleep can often be obtained in the morning as well as the afternoon. Patients of all ages in whom sleep deprivation has been requested are often grateful for morning appointments as they have been awake much of the night. Even without the request of sleep deprivation, a technologist should try to incorporate sleep whenever possible to elicit abnormal spikes or spike waves, especially if a previous EEG without sleep was normal. With that in mind, sleep recordings are typically longer in duration; extra time should be allowed for this when scheduling the initial appointment.
Parents and Caregivers
Parents and caregivers play an important role; in most cases, their presence is beneficial. In the case of infants and younger patients, their right to
be present throughout the EEG. While some parents or caregivers of school-aged children are content to sit outside of the testing area, the vast majority prefer to be present, providing comfort and easing apprehension not only for the patient but also for themselves. Many enjoy the opportunity to rock the child to sleep or stroke the child as it dozes off. The behavior in the vast majority of children is quite satisfactory with the parent or caregiver in attendance. However, in the event of an unruly child, behavior may improve significantly in the absence of these individuals, providing a more disciplined one-on-one partnership between child and technologist. This should be carried out only if the parent or caregiver is in agreement and feels comfortable leaving the recording area.
Some teenagers and adults prefer to have their EEG done in the absence of a family member. For those with special needs, however, it is best to have a person present with whom the patient feels comfortable.
Application of Electrodes
With a nontoxic scalp crayon or washable marker, all heads should be measured utilizing the standard 10–20 measuring system of the International Federation (Jasper, 1958;Saunders, 1979). The scalp is then prepped using a cotton-tipped applicator in conjunction with an abrasive cream, rubbing those areas of scalp where electrodes are to be placed. Doing so eliminates the natural scalp oils, thus reducing the impedance of the skin-to-electrode barrier. A thick conductive paste best combines the requirements for high technical quality with minimal to no scalp irritation. For overnight recordings, the electrodes are best applied to the scalp with collodion, a glue-like substance. A small amount of conductive cream is inserted into each electrode. This application method greatly reduces the pulling or sliding of electrodes during sleep or periods of high activity.
In adults and children over 3 months of age (with a head circumference greater than 40 cm), the full complement of 21 electrodes will ensure adequate coverage for most purposes.
Cardiac leads are recommended for all patients regardless of age or reason for referral, as they help distinguish ECG artifact from EEG abnormality. The addition of cardiac leads has also aided in diagnosing cardiac arrhythmias.
Patients Less than 3 Months of Age
For infants less than 3 months of age or children with head circumferences less than 40 cm, 9 standard electrodes positions (Fp1,2, C3,4, CZ, T3,4, O1,2) are utilized; the longer interelectrode distance allows for easier differentiation and identification of brain rhythms. Respiration, eye, mouth, and cardiac rhythms should also be monitored.
Patients 3 to 12 Months of Age
Performing EEGs on patients of this age is best done with the child placed supine on a stretcher with a rolled up towel under the neck. While the technologist is attempting to measure and place electrodes on an overly tired child, a pacifier or a bottle may provide a calming effect. Interactive toys or books may also be useful in distracting the child's attention. Once appropriate impedances have been established, wrapping the head with gauze is crucial to achieve the following: (a) to secure placement, (b) to keep the leads out of the child's reach, and (c) to aid in eliminating movement artifact while recording. Wrapping the head is imperative in patients under 4 years of age and recommended in older children and some adults whose recording is carried out while supine. Once the head is wrapped, the child may be placed into the arms of a parent and seated in a rocking chair with a blanket. A pillow supporting the parent's arm will provide additional comfort over the following 25 to 45 min recording.
Patients 1 to 4 Years of Age
In this age group, it is vital to obtain 100% of the child's attention. Technologist/child interaction is most important from initial introduction to the onset of the recording. One should speak in a gentle voice using the child's own vocabulary and with much expression. After a very general explanation of the procedure, one should explain each step as it is carried out. The head is measured and the electrodes are applied with the patient supine.
While still capturing the child's attention, the technologist must work quickly to apply the electrodes. At this age, the child's attention span is about 20 min long and his or her cooperation will deteriorate if the period of electrode application extends much beyond this time. Once the electrodes are in place and the head is wrapped, the child may be placed in the rocking chair with a parent or, if calm and relaxed, can remain supine on the stretcher.
Rarely, a poorly behaved and intolerant patient will require restraint of arms. Parental verbal consent should be sought. The following method is found to be practical for the younger half of this age group. Place a narrowly folded sheet under the supine child extending from shoulders to buttock, with excess material hanging at each side of the patient. Place one side of the sheet over the ipsilateral arm, tucking the remainder under the
body, thus rendering the arm immobile. Restrain the other arm in the same fashion.
For a highly agitated child in the upper limit of this age group who repeatedly attempts to detach electrodes while kicking and screaming, despite the assistance of a parent, one may opt for the aid of a “bunting board”, otherwise known as a “papoose”. Again, parental consent is required. This handy tool is similar to a straight-jacket in that the child's body is strapped and its solid backing limits the child's mobility. “Swaddle restraint” is a less favorable option but will suffice in the absence of a bunting board. This requires use of a bed sheet to swaddle the child tightly from shoulders to feet, minimizing trunk and limb movement. Assistance and parental consent is needed. Once the child has been swaddled, continued flailing of the head, attempts to bite, and constant squirming may impair this form of restraint. In this circumstance, the technologist must work quickly, and measuring may have to be omitted. Wrap the head for electrode security and to absorb sweat. Perspiration from the child's strenuous ordeal may increase the difficulty of interpretation. The child will not likely settle at all during electrode application but may do so and perhaps even sleep once the electrodes are secure and the technologist is at a distance. It is often beneficial, in these extreme cases, for the technologist to be clearly out of view, as a simple glance may trigger misbehavior. This method of restraint and measurement omission should be used only as a last resort when multiple attempts of electrode application have been unsuccessful. Sedation effects the EEG and is therefore not an option (see further).
Patients 5 Years of Age to the Elderly
An explanation of the procedure that is appropriate for age is given prior to measuring. The patient is assured that the process is not painful, however a little “scratchiness” may be felt while the scalp is abraded. Throughout the electrode application, the technologist should provide details as to what is being done each step of the way so as to ensure patient comfort and confidence. Electrodes are applied with the patient either supine or seated. Health issues will influence the wiring position. Recording while supine is safer if a seizure or other event occurs. For patients arriving by wheelchair, it is often a wise decision not to redirect them to the stretcher. A patient who is confused or ataxic may indicate the ability and desire to walk but could suffer a fall in doing so. The technologist must always make decisions based on patient safety and err on the side of caution.
For these patients, supplementing a history from the patient or family member will further clarify the EEG's role. For adults with confirmed or suspected seizure disorders, obtain details from someone who has witnessed the attacks. From age 4 years onward, some children are capable of describing auras and later event features as well as adults. Although family or a friend may more precisely describe the seizure characteristics, initiate description of the conditions with the patient when possible.
The International 10–20 Electrode System
For adults and children whose head circumference exceeds 40 cm, a standard allotment of 21 electrodes as well as a ground electrode is utilized. This method of electrode placement has been the standard since 1958, when the International 10–20 System of Electrode Placement was introduced by Jasper. Over the years, minor changes to the measuring system have been used to simplify the process while maintaining the standard 10/20 rules and its precise placement. The following describes our revised method of the 10/20 electrode application. Please refer to Jasper, 1958 for the original 10/20 placement technique.
to locate the horizontal position for CZ. Measuring 10% above the nasion locates the initial horizontal line for FPZ. From FPZ, measure to CZ. Half that distance locates the horizontal position for FZ. From CZ, that same distance is used to create the horizontal positions for PZ and OZ. The 10% horizontal markings above the nasion (FPZ) and inion (OZ) are reference points only, but in some labs including ours, the OZ electrode is placed and used as a reference electrode.
Fig. 9-1. Step 1.
Fig. 9-2. Step 2.
Fig. 9-3. Step 3.
Fig. 9-4. Step 4.
Fig. 9-5. Step 5.
Fig. 9-6. Steps 6 and 7.
prominently recorded than in the A1/2 positions (Fig.9-8). This position can be felt easily while opening and closing the jaw.
Fig. 9-7. Step 8.
Fig. 9-8. Temporal lobe spike distribution. Reproduced from Gibbs and Gibbs, 1952.
Modified 10–20 Electrode System
A modified and much expanded version of the 10–20 system has been termed the 10–10 system (Fisch, 1999) (Fig. 9-9). Although seldom used in its entirety for routine EEGs because of the plethora of electrodes involved, it may depict spike and other fields more precisely. This is best created by surrounding an “active” focus with a series of eight additional electrodes, constituting a scalp grid of closely spaced electrodes surrounding the active focus. Subsequent recording employs referential or bipolar montages or both. Note the addition of newly labeled electrodes with the 10–10 system.
Scalp Lesions, Incisions, and Asymmetrical Heads
If scalp lesions and incisions are situated in areas directly related to electrode positioning, one must accommodate placement by relocating the electrode either anterior, posterior, or lateral to the lesion. Electrodes to be placed on the opposite side of the head must be similarly relocated to
maintain symmetry. If standard midline positioning is not possible, the involved electrode can be relocated slightly anterior or posterior along the midline plane.
Fig. 9-9. 10-10 system (a portion thereof).
The application of electrodes to patients with deformed or asymmetrical heads is a more cumbersome task requiring a more pragmatic approach. The 10–20 measuring technique is used where possible. Some circumstances require technologist scrutiny rather than measurement to estimate electrode placement. In this instance, anatomical landmarks should be considered more than electrode symmetry. If the hemicrania are not similar in size, each hemisphere must be measured independently; this will generally produce bilateral symmetry of electrode positions. Technologist annotation regarding any displaced electrodes is necessary.
Recording Children and Adults
After electrode application, impedances of all electrodes must be measured and their values indicated at the onset and preferably offset of each EEG. Wrapping of the head is optional in cooperative adults but deemed necessary in most children.
In adults, the typical sensitivity used for recording EEG activity is 5 to 7 µV/mm. Because the voltage of EEG activity in children usually exceeds that of adults, a sensitivity of 10 to 15 µV/mm is more likely to produce readable recordings. Low frequency filter settings of 1 and 0.3 Hz most often achieve the best compromise between the depiction of delta activity and curtailment of artifact. High frequency filter should be 70 Hz or more so as to avoid blunting or diminution of spikes and high frequency potentials. The 60 Hz filter should be off. These suggested settings are only guidelines; therefore, the technologist must be knowledgeably prepared to adjust the instrument controls to the particular recording situation.
For a technically satisfactory EEG, the minimum recording duration is 20 minutes, not inclusive of activating procedures (American Clinical Neurophysiology Society, 1994). Sleep, hyperventilation, and photic stimulation can extend the recording time considerably. Children's EEGs are typically of longer duration, as time is often necessary for the value of sleep to be obtained.
Prior to commencing the EEG, any gum or candy must be removed, as this will create significant artifact. Offering a bottle or soother to calm an agitated child may create sucking artifact initially in the EEG; however, with patience, the technologist is often rewarded by the “ultimate goal”—a relaxed patient who eventually falls asleep.
Inform the patient that eye closure will occupy the bulk of the recording and that there will be no associated discomfort at any time. Indicate that a 3 to 4 minute session of hyperventilation and photic stimulation may be carried out. Encourage sleep. Once the recording has been initiated, noise within and outside the room should be kept to a minimum. A sign on the recording room door reading “Quiet, Sleep Recording in Progress” is useful. The ringer on the room phone as well as the patient's cell phone, if present, should be turned off. Remind parents and caregivers that talking, coughing, clearing the throat, and so on will be enough to rouse a patient from light sleep to wakefulness. If young siblings are present, one should encourage that they remain outside of the recording room with a parent.
As a security measure, during the electrode application and recording of all patients, both side rails of a stretcher are placed in the upright position regardless of age. The only exception to this arises when a parent or caregiver is standing at the patient's side, providing comfort by holding his or her hand or rubbing the patient's back. This, along with dimmed lighting and soft music, promotes relaxation and sleep. If a young patient is wide awake and sleep is doubtful, a parent can read the child a story while the child remains in a relaxed, supine position.
Record continuously, as significant abnormalities may appear in only one state. Obtain drowsiness and sleep whenever possible, since sleep phenomena (V waves and spindles) may be absent or asymmetrical in some individuals. Sleep activates many EEG abnormalities.
Passive Eye Closure (PEC)
PEC can elicit “background” rhythms when an alert patient will not close the eyes on request. The technologist, patient or parent gently places his or her fingers over the eyes (without interfering with frontal polar electrodes) and counts to 10. PEC may create resistance and augment crying, movement, or laughter. Despite the various muscle and movement artifacts it may create, PEC remains an essential tool to elicit and determine the normality of background activity in an otherwise uncooperative individual.
Continuous recording during drowsiness, sleep, and arousal is essential, as abnormalities may appear only during these times. As generalized abnormalities are often induced by arousal, montages favoring their
expression are preferred, e.g. ipsilateral ear reference. Calming and reassuring the patient when rousing in a strange environment will minimize electrode artifact.
Performing HV for 3 to 4 minutes can elicit focal or diffuse abnormalities. It is performed routinely in recordings with minimal or no epileptiform activity and thus, usually is performed later in the EEG. However, HV early in the recording, after initially assessing EEG characteristics, may relax a patient and promote sleep or provide the opportunity for a second HV if results of the first are equivocal. Preferred montages for HV include anterior–posterior bipolar montage or ipsilateral ear reference. The level of patient effort should be annotated and 3 post-HV minutes allowed before changing montages or terminating the recording. HV is stopped if definite spike–waves occur in order to avoid absence status epilepticus or a generalized tonic–clonic seizure.
Some children as young as 2 years can hyperventilate by blowing on a plastic pinwheel or a tissue. Constant encouragement for continued effort is vital in children and in some adults. More than in adults, children can produce a significantly greater “buildup” effect with very high voltage slow waves during the course of HV, and spike–wave discharges may be difficult to appreciate. This intense HV buildup should return to baseline within 2 min after HV. The technologist should assure that the patient has stopped hyperventilating when so requested.
Contraindications to hyperventilation are previous cerebral hemorrhage, cardiac history, severe large vessel stenosis, confused state, pregnancy, asthma, or spike–waves on recording. In our laboratory, hyperventilation is not carried out on individuals more than 60 years of age unless they appear healthy and deny the above medical conditions.
Photic Stimulation (PS)
Intermittent photic stimulation may produce a photoparoxysmal response (PPR) that is useful in identifying some epilepsy syndromes, especially those originating in childhood. A sequence of flashes from a strobe light positioned approximately 30 cm from the patient is utilized (Fisch et al., 1999). In our laboratory, the flash-rate sequence is 1, 3, 6, 9, 12, 15, 18, 21, 25, and 30 Hz, each for a duration of 8 to 10 seconds. A minimum of 4 seconds should elapse between application of each flash rate to avoid lowering the PPR threshold and thus initiating a generalized tonic–clonic seizure.
The lowest threshold for provocation of a PPR is a flash rate between 12 and 20 Hz upon eye closure including forceful eye closure by the patient (Striano et al., 2009). Thresholds are higher with eyes closed and particularly with eyes open. Therefore, for safety, photic stimulation should begin with eyes open at low flash rates; if a PPR should occur under such usually high threshold conditions, it should not be continued without consultation with a physician. If a PPR occurs, the strobe must be stopped immediately to prevent progression to a generalized seizure. Since spontaneous spike–waves may occur coincidentally during photic stimulation, one must attempt to establish a causal link by pursuing cautious attempts at its reproduction using the identical flash rate. Further attempts at slightly higher and slightly lower flash rates should be carried out to determine the patient's light-sensitivity threshold and range. If the spike–waves cannot be reproduced, PS is continued with caution; otherwise, this activating procedure should be terminated. Unlike HV, photic stimulation can be attempted in patients with known epileptiform abnormalities, the exception to this being status epilepticus.
Contraindications for photic stimulation would be status epilepticus, recent cataract surgery, intracranial hemorrhage, and possibly migraine.
Some patients, such as those with infantile spasms, myoclonic epilepsies, and mesial hemispheric epilepsy may have startle-induced seizures. During the recording when the patient is calm and quiet, the technologist may clap his or her hands unexpectedly, attempting to record such.
Accurate and complete annotation of the clinical state of the patient throughout the recording is vital. Annotating the lack of clinical events (i.e., no eye movement) is just as important as annotating events themselves and is very useful for the reading electroencephalographer. Such measures will enable the physician to identify confidently abnormalities that may be simulated by artifact. These include differentiation of spike–wave discharges from sobbing, posterior delta activity from head movement, and periodic sharp waves from hiccupping. Since the state of alertness and the accompanying electrographic changes are more variable in children, both negative and positive phenomena should frequently be annotated. It is imperative during a clinical event or electrographic seizure that clinical data (or their lack) be annotated in detail for patients of all ages.
A technologist aware that sedation can be used does not develop techniques designed to elicit best cooperation, as would a technologist who works in a laboratory that does not use sedation. Sedation may have a paradoxical effect on children with behavioral disorders. Sedation injects beta and theta into the EEG that may mask some abnormalities. In our laboratory, sedation is utilized only in children who have severe behavioral disorders, equivalent to fewer than 1% of all children seen. The corollary to this is that EEGs should not be scheduled on the same day as other tests requiring sedation, such as neuroimaging.
Recording in an Intensive Care Environment
The EEG machine must be positioned securely on an easy-to-maneuver base with wheels able to enter and exit elevators without difficulty. Space is limited in intensive care areas and one must weave in and around respiratory devices, patient lines, tubing, and other devices.
Wash your hands and wear gloves. Gowns and appropriate masks are necessary for high-risk patients, with droplet precautions or infectious conditions.
Start the EEG machine, input patient data, and create a new study prior to any patient contact thus avoiding patient to machine contamination. Access the electrode impedance screen which will disclose any high-impedance electrodes as they are applied.
Place all materials required to measure and affix electrodes on a face cloth at the head of the bed. These include a tape measure, scalp crayon or washable marker, tongue depressor containing both the conductive and abrasive creams, as well as 1″ ÷ 1″ disposable squares, which help secure each electrode to the scalp. Two to four cotton-tipped swabs are needed to abrade the scalp of an average patient; however, the quantity may increase or even double when dealing with a postoperative or posttraumatic patient with other contaminants such as blood or iodine remaining on the scalp. If the patient is not sedated and is agitated, it is recommended to wrap the head with gauze to keep the electrodes intact.
Secure the electrode head box firmly to an IV pole or other stable object behind the head of the patient. Its height should be at a level at which the electrodes hang freely without being contaminated by contacting the floor. Measuring the head and applying electrodes is more easily done while standing behind the patient rather than on one side for two reasons: (1) this eliminates the need to physically alternate from one side of the patient to the other during both the measuring and application and (2) it offers a bird's-eye view of the head dimensions with easy access to all electrode positions, skull defects, incisions, ventricular drains, and other objects.
A rolled up towel serves well under the neck of the patient, allowing easier access to the occipital regions. Always request consent to do so as the patient may have suffered cervical spine injuries and therefore, manipulation of the head could be detrimental to his or her well-being. If a cervical collar is present and positioning for O1/2 cannot be accessed, placement of these electrodes can be applied more anterior than usual but annotation must be clearly indicated.
Measure the head and apply electrodes according to the 10–20 system as described above. ECG leads should be included. Visually scan the electrode impedances on the EEG machine and, if required, further abrade the scalp in positions where impedances remain high until they are satisfactory. If the impedance on a single electrode is not responding at all after further abrasion and reapplication, the electrode is likely faulty. Once all impedances are appropriate, you may carefully back away from the patient, remove your gloves, wash your hands, and reapply a fresh pair of gloves to be used while operating the EEG machine. Commence recording.
Montages and machine settings in the intensive care environment are similar to those used to record routine EEGs in the lab. On some occasions, however, settings may have to be adjusted appropriately depending on EEG findings, e.g. suppression.
For patients whose level of consciousness is impaired, both auditory and painful stimulation should be carried out. Auditory stimulation consists of (1) making loud clapping sounds near the patient's ear; (2) calling the patient's name several times and presenting a simple command, such as “open your eyes”; or (3) asking the patient to squeeze your hand. These methods help to determine the patient's cognitive state.
Typical methods of painful stimulation consists of (1) moderate to deep nail-bed pressure to digits of the hands or feet lasting 2 to 3 s, (2) sternal rub, (3) suctioning of the patient by the nurse, (4) nasal tickle, and (5) passive eye opening and closing (Ramachandrannair et al., 2005). It is crucial to indicate any clinical findings related to these forms of stimulation, such as the withdrawal of a limb, opening of the eyes, grimacing, shoulder abduction, or deviation of the head. Of equal importance is the lack of clinical findings, which should also be annotated. In some instances, a change in EEG activity can be evident in simple procedures such as oral cleansing or drawing blood. With both auditory and painful stimulation, it is imperative that technologist annotation (i.e., “pain on,” “pain off”) is time-linked with the stimuli.
Should a patient appear to be in clinical or subclinical status epilepticus, the technologist should contact the neurologist or attending physician with any concerns while the machine is still recording. The physician involved may wish to view the ongoing EEG personally and, if status is suspected, the decision to offer medication such as IV diazepam or midazolam in attempts to abolish the ongoing electrographic seizure activity may be carried out. In the case of EEGs demonstrating nonconvulsive status epilepticus, providing continuous monitoring for days is often sought. Electrodes in these cases are best applied using collodion as opposed to paste for a technically better recording. Ideally, subdermal wire electrodes offer the best results for high-quality EEGs (Young et al., 2006). In such patients, continuous monitoring helps the physician to establish and monitor appropriate therapeutic options as well as to visually establish the progression or termination of the seizure activity (Claassen et al., 2004).
When prolonged monitoring is required, the leads remain in place, wrapped firmly with gauze and monitored until further notice. The recording should be routinely scrutinized by the technologist once or twice each day in order to assure its technical quality. For those patients not in status, the electrodes can be removed, then washed with soap and water in the lab and sterilized. If the patient is considered at high risk for infection, all equipment—including the EEG machine, its cables, the electrodes, measuring tape, and crayon—must be sterilized using an antibacterial wash. Wash hands before leaving the intensive care area.
Many comatose patients have their eyes open or closed for the entire recording. Some will blink spontaneously. For those whose eyes remain closed, it is valuable to hold the eyes open for 10 to 20 s during the EEG, annotating any clinical findings such as deviation, hippus, or nystagmoid movements. Holding the eyes closed in patients who tend to keep them open may help eliminate eye movement artifact and better distinguish these from triphasic waves or periodic discharges. Annotation of any eye movement felt during this epoch of eye closure is important.
When electrocerebral silence (ECS) is questioned, minimal technical standards exist (American Clinical Neurophysiology Society, 2006). These life-determining EEGs should be carried out only by an experienced technologist. The initial recording should consist of a full complement of electrodes based on the 10–20 system. Subsequent recordings, which are highly recommended, should be carried out using longer interelectrode distances, no less than 10 cm apart, to improve visualization of cerebral potentials. Electrode impedances should all read less than 10,000 but greater than 100 Ω and should be indicated at the beginning and end of the recording. Adequate calibration procedures are essential, as are appropriate filter settings. Sensitivity at the onset of the recording may be 7 or 5 µV/mm but must be increased to at least 2 µV/mm for a minimum duration of 30 min of the recording. At this sensitivity, artifacts of various origins—including physiological, mechanical, electromagnetic, or electrostatic—will be augmented and must be identified and proven as such by the technologist. ECG must be recorded; respirations can be monitored visually with close observation accompanied by simultaneous annotation or more easily by using a respiration monitor. The use of some critical care equipment during an EEG may create prominent artifact; such equipment includes Prisma (a hemoperfusion machine), electronic physiological equipment (either handheld or vibrating bed), electronic infusion pumps, and even condensed water in ventilator tubings (Young & Campbell, 1999; Young et al., 2002; Young et al., 2007). Date of recording as well at start and stop times must be indicated.
The patient's core body temperature must be annotated. In addition, it is important to record all patient medications, dosages, and time of last administration, as they too may play a role in cerebral inactivity.
As elaborated above, intense auditory and painful stimulation can be performed to establish whether any electrographic reactivity is present. It may also be useful to compare lack of reactivity with that of previous EEGs. However, its value with the needed high sensitivities is lessened by the inevitable artifact associated with its application. Therefore, our laboratory has abandoned such stimuli for ECS recordings.
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