EEG Routine 2 — Questions and Answers
Question 1: What is the standard duration of a routine EEG recording?
- 5-10 minutes
- 20-30 minutes (Correct answer)
- 60-90 minutes
- 4-6 hours
Correct answer: 20-30 minutes
A standard routine EEG typically records for 20-30 minutes, providing adequate time for baseline recording, activation procedures (hyperventilation and photic stimulation), and ideally capturing some drowsiness.
The routine EEG follows a standardized protocol of 20-30 minutes total recording time. This includes: (1) initial baseline recording during relaxed wakefulness with eyes closed (5-10 minutes); (2) eye opening/closing to assess alpha reactivity; (3) hyperventilation for 3 minutes with post-HV recording; (4) intermittent photic stimulation at various frequencies; (5) ideally, some drowsiness or sleep. The ACNS recommends at least 20 minutes of interpretable recording. If sleep is not achieved, the diagnostic yield decreases since many epileptiform discharges appear during drowsiness and NREM sleep. Extended routine recordings (1-2 hours) or sleep-deprived EEGs may be ordered when the initial study is non-diagnostic.
Question 2: Before beginning a routine EEG, the technologist should first:
- Apply all electrodes and begin recording immediately
- Review the clinical history and indication for the study on the requisition (Correct answer)
- Perform hyperventilation testing
- Administer a sedative if the patient appears anxious
Correct answer: Review the clinical history and indication for the study on the requisition
Reviewing the clinical indication and patient history before beginning allows the technologist to tailor the recording protocol, anticipate relevant findings, and take appropriate precautions.
Before applying electrodes, the technologist should review the clinical requisition for: (1) indication (seizures, altered mental status, pre-surgical evaluation); (2) relevant medical history (epilepsy type, medications, prior EEG findings); (3) contraindications to activation procedures (stroke for HV, photosensitive epilepsy for photic stimulation); (4) special considerations (skull defects, EVDs, scalp wounds). The patient should then be identified, the procedure explained, and consent obtained. Current medications should be documented as they affect the EEG (benzodiazepines increase beta, anticonvulsants may suppress epileptiform activity). This preparation ensures a targeted, safe, and diagnostically optimal recording. Rushing to electrode application without clinical context is the most common cause of suboptimal studies.
Question 3: During a routine EEG, the technologist observes the patient staring blankly and becoming unresponsive. The appropriate action is to:
- Immediately stop the recording and call a code
- Continue recording while testing the patient's responsiveness and documenting observations (Correct answer)
- Disconnect the electrodes to examine the patient
- Wait until the episode ends to note it in the report
Correct answer: Continue recording while testing the patient's responsiveness and documenting observations
The technologist should keep recording to capture the EEG correlate of the clinical event while simultaneously testing responsiveness (speaking to the patient, presenting objects) and carefully documenting all observations with timestamps.
When a clinical event occurs during EEG, the recording must continue as the electrographic correlate is the primary diagnostic goal. The technologist should: (1) note the exact time of onset; (2) test responsiveness by speaking to the patient, asking them to remember a word, or showing an object; (3) observe and document the semiology — where movement begins, lateralization, eye deviation, automatisms, vocalization; (4) test for motor function (hold arms out); (5) time the duration; (6) assess post-event confusion and when normal responsiveness returns; (7) add detailed annotations to the recording. Testing during the event helps differentiate absence seizures (unresponsive, no memory) from focal seizures with impaired awareness from non-epileptic events. The technologist's clinical observations are often as valuable as the EEG tracing itself.
Question 4: What documentation should the EEG technologist include in the technical report for a routine study?
- Only the start and end time of the recording
- Patient state, medications, impedance values, activation procedure details, artifacts encountered, and any clinical events observed (Correct answer)
- Just the montages used during the recording
- A diagnosis based on the EEG findings
Correct answer: Patient state, medications, impedance values, activation procedure details, artifacts encountered, and any clinical events observed
The technical report should comprehensively document patient state, current medications, electrode impedances, activation procedures performed and their responses, artifacts encountered, clinical observations, and any events during the recording.
A complete EEG technical report includes: (1) patient demographics and clinical indication; (2) medications and time of last dose; (3) patient state throughout recording (awake, drowsy, asleep); (4) electrode application method and impedance values; (5) montages and filter settings used; (6) activation procedures — HV quality and duration, photic stimulation frequencies used; (7) artifact documentation and steps taken to reduce them; (8) any clinical events with detailed behavioral descriptions and timestamps; (9) patient cooperation level; (10) total interpretable recording time; (11) technologist's name and credentials. The technologist should NOT provide a diagnostic interpretation but may note obvious technical observations. This documentation is crucial for the interpreting physician and becomes a permanent part of the medical record.
Question 5: If a routine EEG shows no epileptiform abnormalities, this means:
- The patient definitely does not have epilepsy
- A single normal EEG does not exclude epilepsy, as interictal sensitivity is approximately 50% for a single routine study (Correct answer)
- The patient's medication should be stopped immediately
- No further testing is needed
Correct answer: A single normal EEG does not exclude epilepsy, as interictal sensitivity is approximately 50% for a single routine study
A single normal routine EEG has limited sensitivity (approximately 50%) for detecting interictal epileptiform discharges. Epilepsy remains a clinical diagnosis, and serial or prolonged EEG studies increase diagnostic yield.
The sensitivity of a single routine 20-30 minute EEG for detecting interictal epileptiform discharges (IEDs) in patients with epilepsy is approximately 29-55%. This means 45-71% of patients with epilepsy may have a normal first EEG. Serial EEGs increase cumulative yield: two studies reach approximately 70-80%, and four studies approximately 90%. The limited sensitivity results from: (1) temporal sampling — IEDs may not occur during the brief recording; (2) spatial sampling — deep or small foci may not reach scalp electrodes; (3) medication effects suppressing IEDs. A normal EEG never excludes epilepsy, which remains a clinical diagnosis based on history. When clinical suspicion is high despite normal routine EEG, options include sleep-deprived EEG, prolonged ambulatory EEG, or inpatient video-EEG monitoring.
Question 6: The standard paper speed (or digital equivalent time base) for routine EEG display is:
- 15 mm/second
- 30 mm/second (Correct answer)
- 60 mm/second
- 120 mm/second
Correct answer: 30 mm/second
The standard time base for routine EEG is 30 mm/second (equivalent to displaying 10 seconds per standard screen page), which provides optimal visualization of EEG waveform morphology and temporal relationships.
The standard EEG display speed of 30 mm/second (also expressed as 10 seconds per page on digital systems) has been the convention since paper EEG days. At this speed, one second of EEG occupies 30 mm, providing optimal visualization of frequency, morphology, and temporal relationships. A 10-Hz alpha wave appears with peaks approximately 3 mm apart, easily recognizable. Slower speeds (15 mm/s, 20 seconds/page) compress the tracing and are useful for identifying slow trends, seizure evolution patterns, or reviewing long recordings quickly. Faster speeds (60 mm/s) spread out the tracing and can help analyze fast activity or spike morphology. Neonatal EEG often uses 15 mm/s because the slow frequencies of neonatal EEG are better visualized at compressed time bases.
EEG Routine 2
What is the standard duration of a routine EEG recording?