Select the correct order from greatest to least for the sensitivity of neurophysiologic monitoring techniques to volatile anesthetics (SSEP; VEP; BAEP).

Select the correct order from greatest to least for the sensitivity of neurophysiologic monitoring techniques to volatile anesthetics (SSEP; VEP; BAEP).

• A. SSEP > VEP > BAEP
• B. VEP > SSEP > BAEP
• C. BAEP > VEP > SSEP
• D. SSEP > BAEP > VEP

Answer: (B)

The key idea is how much different neurophysiologic signals ride the depressant effects of volatile anesthetics. These agents dampen cortical activity more than brainstem activity, so potentials generated by the cortex are more affected than those from lower brain regions. Visual evoked potentials rely on processing in the occipital cortex. As depth of anesthesia increases, cortical excitability drops markedly, causing large reductions in amplitude and longer latencies. Somatosensory evoked potentials involve pathways from peripheral nerves up to the cortex but also have a substantial subcortical and brainstem component; they’re reduced by anesthesia, but not as dramatically as visual cortical potentials. Brainstem auditory evoked potentials originate in the brainstem and are less susceptible to the depressive effects of volatile agents, so their amplitudes are relatively preserved compared with the cortical-based responses. Putting that together, the most sensitive to volatile anesthetics is the visual evoked potential, followed by somatosensory evoked potentials, with brainstem auditory evoked potentials being the least sensitive. This makes the order from greatest to least sensitivity VEP, SSEP, BAEP. Clinically, that means VEPs tend to become unreliable earlier as anesthesia depth increases, whereas BAEPs tend to remain usable longer.

The key idea is how much different neurophysiologic signals ride the depressant effects of volatile anesthetics. These agents dampen cortical activity more than brainstem activity, so potentials generated by the cortex are more affected than those from lower brain regions.

Visual evoked potentials rely on processing in the occipital cortex. As depth of anesthesia increases, cortical excitability drops markedly, causing large reductions in amplitude and longer latencies. Somatosensory evoked potentials involve pathways from peripheral nerves up to the cortex but also have a substantial subcortical and brainstem component; they’re reduced by anesthesia, but not as dramatically as visual cortical potentials. Brainstem auditory evoked potentials originate in the brainstem and are less susceptible to the depressive effects of volatile agents, so their amplitudes are relatively preserved compared with the cortical-based responses.

Putting that together, the most sensitive to volatile anesthetics is the visual evoked potential, followed by somatosensory evoked potentials, with brainstem auditory evoked potentials being the least sensitive. This makes the order from greatest to least sensitivity VEP, SSEP, BAEP. Clinically, that means VEPs tend to become unreliable earlier as anesthesia depth increases, whereas BAEPs tend to remain usable longer.