Anesthesia Effects on Neurophysiological Monitoring Flashcards

Hypothermia intraoperatively affects all evoked potential modalities primarily by:

Answer: Prolonging latencies proportionally to the degree of temperature decrease

Hypothermia slows axonal conduction velocity in a temperature-dependent manner, increasing latencies across all evoked potential modalities proportionally to the degree of cooling.

Hemodilution during major surgery affects SSEP monitoring by:

Answer: Reducing SSEP amplitudes when hematocrit drops below critical oxygen delivery levels

Severe hemodilution reduces oxygen-carrying capacity; when hematocrit falls below critical levels, neural ischemia can cause SSEP amplitude reduction, requiring distinction from surgical injury.

Intraoperative hypertension (high MAP) generally affects evoked potential monitoring by:

Answer: Having minimal direct effect on evoked potentials within the range of cerebral autoregulation

Within the cerebral autoregulation range, moderate hypertension has minimal direct effect on evoked potentials; however, extreme hypertension can cause hyperemia or breakthrough changes.

Benzodiazepines administered intraoperatively affect SSEP monitoring by:

Answer: Moderately reducing cortical SSEP amplitudes with minimal subcortical effects

Benzodiazepines cause moderate, dose-dependent reductions in cortical SSEP amplitudes through GABA-A receptor potentiation, while subcortical components are relatively spared.

If volatile anesthetic cannot be discontinued before a critical monitoring phase of surgery, the neurophysiologist should:

Answer: Establish new baselines at the current anesthetic level and monitor for changes from those baselines

When volatile anesthetic cannot be reduced, establishing new baselines at the stable anesthetic concentration allows meaningful monitoring by tracking changes from the current pharmacological baseline.

The addition of 50% nitrous oxide to TIVA primarily affects MEP monitoring by:

Answer: Significantly reducing MEP amplitudes and increasing the risk of complete MEP loss

Adding 50% nitrous oxide to propofol TIVA significantly reduces MEP amplitudes, with the combined effect sometimes causing complete MEP loss and warranting avoidance during MEP monitoring.