CNIM Somatosensory Evoked Potentials (SSEP) 2 — Questions and Answers
Question 1: Which filter settings are typically used for intraoperative SSEP recording?
- 1–30 Hz bandpass
- 30–3000 Hz bandpass (Correct answer)
- 0.1–10 Hz bandpass
- 3000–10000 Hz bandpass
Correct answer: 30–3000 Hz bandpass
SSEP recordings typically use a bandpass filter of 30–3000 Hz to capture the relevant frequency components of evoked potential waveforms while reducing low-frequency drift and high-frequency noise.
Question 2: What is the recommended number of averages to obtain a reliable SSEP waveform in the operating room?
- 10–20
- 50–100
- 200–500 (Correct answer)
- 1000–2000
Correct answer: 200–500
Typically 200–500 sweeps are averaged intraoperatively to achieve an acceptable signal-to-noise ratio for SSEP waveforms.
Question 3: Bilateral loss of SSEP signals with preserved baseline recordings most likely indicates:
- Equipment failure only
- A systemic physiological change such as hypotension or hypothermia (Correct answer)
- Unilateral cord injury
- Normal response to anesthesia deepening
Correct answer: A systemic physiological change such as hypotension or hypothermia
Simultaneous bilateral SSEP loss typically suggests a systemic cause such as severe hypotension, hypothermia, or anesthetic changes rather than a focal surgical injury.
Question 4: Which anesthetic agent has the least suppressive effect on cortical SSEP amplitudes?
- Isoflurane at 1.5 MAC
- Propofol-based total intravenous anesthesia (TIVA) (Correct answer)
- Halothane at 1 MAC
- Nitrous oxide 70%
Correct answer: Propofol-based total intravenous anesthesia (TIVA)
Propofol-based TIVA has the least suppressive effect on cortical SSEP amplitudes compared to volatile inhalational agents, making it preferred for cases requiring sensitive monitoring.
Question 5: The stimulation rate for median nerve SSEP should avoid multiples of 60 Hz to prevent:
- Nerve damage from overstimulation
- Electrical line noise contamination (Correct answer)
- Muscle artifact from repetitive stimulation
- Cortical spreading depression
Correct answer: Electrical line noise contamination
Stimulation rates that are multiples of 60 Hz can alias with power line frequency, contaminating the averaged SSEP with electrical noise rather than canceling it.
Question 6: During prone positioning for spinal surgery, SSEPs are lost immediately after positioning. The most appropriate first step is to:
- Alert the surgeon of spinal cord injury
- Check for brachial plexus stretch or peripheral nerve compression at pressure points (Correct answer)
- Increase stimulation intensity to maximum
- Discontinue monitoring
Correct answer: Check for brachial plexus stretch or peripheral nerve compression at pressure points
Immediate post-positioning SSEP loss most often results from peripheral nerve compression or brachial plexus stretch due to improper positioning rather than spinal cord injury.
CNIM Somatosensory Evoked Potentials (SSEP) 2
Which filter settings are typically used for intraoperative SSEP recording?