CNIM Anesthesia Effects on Neurophysiological Monitoring 2 — Questions and Answers
Question 1: Dexmedetomidine's effect on intraoperative SSEP and MEP monitoring is best described as:
- Profound suppression requiring cessation before monitoring
- Mild to moderate amplitude reduction with relative preservation at typical clinical doses (Correct answer)
- Complete abolition of cortical potentials
- No measurable effect on any evoked potential
Correct answer: Mild to moderate amplitude reduction with relative preservation at typical clinical doses
Dexmedetomidine causes mild to moderate, dose-dependent reductions in SSEP and MEP amplitudes at typical clinical infusion rates but is generally compatible with intraoperative monitoring.
Question 2: A sudden uniform decrease in SSEP and MEP amplitudes occurs during a propofol bolus. The most appropriate neurophysiologist action is:
- Immediately alert surgeon of possible spinal cord injury
- Note the timing of the bolus, communicate with the anesthesiologist, and wait for stabilization (Correct answer)
- Increase stimulus intensity immediately
- Discontinue monitoring
Correct answer: Note the timing of the bolus, communicate with the anesthesiologist, and wait for stabilization
Anesthetic bolus-related changes are transient; communicating with the anesthesiologist and documenting the timing prevents false positive surgical alarms and allows appropriate interpretation.
Question 3: The effect of increasing volatile anesthetic from 0.5 MAC to 1.5 MAC on SSEP cortical responses is:
- Amplitude increase with latency decrease
- Amplitude decrease and latency prolongation in a dose-dependent manner (Correct answer)
- No change in amplitude or latency
- Selective loss of subcortical components only
Correct answer: Amplitude decrease and latency prolongation in a dose-dependent manner
Volatile anesthetic agents cause dose-dependent SSEP amplitude decreases and latency prolongation, with the cortical N20/P37 responses being most sensitive to MAC increases.
Question 4: When SSEP baselines cannot be established after induction due to poor signal quality, the FIRST troubleshooting step should be:
- Request anesthesia change to TIVA immediately
- Check electrode impedances, stimulator connections, and patient positioning (Correct answer)
- Increase the number of averages to 2000+
- Abandon monitoring for the case
Correct answer: Check electrode impedances, stimulator connections, and patient positioning
Technical factors (high impedance, poor electrode contact, stimulator disconnection, positioning artifacts) are the most common causes of absent baselines and should be systematically excluded first.
Question 5: Why should anesthetic changes be communicated to the neurophysiologist in real-time during surgery?
- To satisfy accreditation documentation requirements
- So the neurophysiologist can correlate anesthetic-induced changes with evoked potential waveforms and avoid false alarms (Correct answer)
- To determine surgical billing codes
- To assess patient pain levels
Correct answer: So the neurophysiologist can correlate anesthetic-induced changes with evoked potential waveforms and avoid false alarms
Real-time communication of anesthetic changes allows the neurophysiologist to distinguish drug-induced signal changes from surgically induced neural injury, preventing false positive alarms.
Question 6: Mean arterial pressure (MAP) below what threshold is considered physiologically significant for intraoperative SSEP monitoring?
- Below 100 mmHg
- Below 80 mmHg
- Below 60 mmHg (Correct answer)
- Below 40 mmHg
Correct answer: Below 60 mmHg
MAP below 60 mmHg is generally considered the threshold below which cerebral and spinal cord perfusion may be compromised, causing ischemia-related SSEP amplitude decreases.
CNIM Anesthesia Effects on Neurophysiological Monitoring 2
Dexmedetomidine's effect on intraoperative SSEP and MEP monitoring is best described as: