Which SSEP waveforms are least impacted by anesthesia?

The choice indicating that peripheral nerve N9 waveforms are least impacted by anesthesia is grounded in the physiological principles of evoked potentials. The N9 waveform is generated close to the peripheral nerve segment and reflects the sensory nerve response occurring before influences from central processes are involved. As a result, it is less affected by the systemic changes brought about by anesthesia, which primarily influences cortical and subcortical activity.

Anesthesia tends to alter brain function, affecting waveforms that originate at the cortical and subcortical levels, such as the cortical (N20/P23, P37/N45) and subcortical (P14, N13, P31) waveforms. These waveforms are more susceptible to the depressant effects of anesthetics on synaptic transmission and neuronal excitability, resulting in diminished amplitude or delayed latencies.

In contrast, peripheral nerve waveforms like N9 retain their integrity because they predominantly reflect the conduction of signals along the nerve itself rather than synaptic activity in the brain, making them more reliable under anesthetic conditions. Thus, the N9 waveform stands out as the one least impacted by anesthesia.