CNIM Electroencephalography (EEG) in the Operating Room 1 — Questions and Answers
Question 1: What is the standard electrode placement system used for intraoperative EEG monitoring?
- 10-20 International System (Correct answer)
- 10-10 Extended System
- Modified Combinatorial Nomenclature
- Bipolar Anterior-Posterior System
Correct answer: 10-20 International System
The 10-20 International System is the universally accepted standard for scalp electrode placement in both routine and intraoperative EEG.
Question 2: Which EEG frequency band is typically dominant during relaxed wakefulness with eyes closed?
- Delta (0.5–4 Hz)
- Theta (4–8 Hz)
- Alpha (8–13 Hz) (Correct answer)
- Beta (13–30 Hz)
Correct answer: Alpha (8–13 Hz)
Alpha rhythm (8–13 Hz) is the dominant posterior rhythm during relaxed wakefulness with eyes closed, and is attenuated by eye opening or mental effort.
Question 3: What type of EEG montage references each electrode to the mathematical average of all scalp electrodes?
- Bipolar chain montage
- Linked-ears referential montage
- Common average reference montage (Correct answer)
- Laplacian montage
Correct answer: Common average reference montage
The common average reference montage subtracts the mean signal of all scalp electrodes from each individual channel, minimizing bias from any single reference site.
Question 4: Which filter setting is MOST appropriate for eliminating 60 Hz power line interference in intraoperative EEG?
- High-pass filter at 70 Hz
- Notch filter at 60 Hz (Correct answer)
- Low-pass filter at 1 Hz
- Band-pass filter at 100–300 Hz
Correct answer: Notch filter at 60 Hz
A 60 Hz notch filter selectively removes power line artifact while preserving all clinically relevant EEG frequency bands.
Question 5: What electrode impedance level is considered acceptable for reliable intraoperative EEG recording?
- Less than 5 kΩ (Correct answer)
- 10–20 kΩ
- 25–50 kΩ
- Greater than 100 kΩ
Correct answer: Less than 5 kΩ
Electrode impedances below 5 kΩ ensure good electrical contact, minimizing artifact and maintaining signal integrity in the OR environment.
Question 6: What does increasing the 'sensitivity' setting on an EEG machine accomplish?
- It increases the number of electrodes sampled per second
- It reduces the amplitude of the displayed waveforms by increasing the µV/mm value
- It enlarges the displayed waveforms by decreasing the µV/mm value (Correct answer)
- It shifts the recording bandwidth toward higher frequencies
Correct answer: It enlarges the displayed waveforms by decreasing the µV/mm value
Decreasing the µV/mm value (increasing sensitivity) makes waveforms appear taller on the display, useful for visualizing low-amplitude EEG activity.
Question 7: In intraoperative EEG, a bipolar montage differs from a referential montage in that it:
- Compares each electrode to a single distant reference
- Compares adjacent electrodes to one another in a chain (Correct answer)
- Averages all electrodes into a single summary channel
- Uses only four electrodes placed over the temporal lobes
Correct answer: Compares adjacent electrodes to one another in a chain
A bipolar montage records the voltage difference between pairs of adjacent electrodes, forming a chain that helps localize focal abnormalities.
CNIM Electroencephalography (EEG) in the Operating Room 1
What is the standard electrode placement system used for intraoperative EEG monitoring?