When used as an induction agent, which of the following drugs will have the least effect on the SSEP?

The least effect on somatosensory evoked potentials (SSEP) among the drugs listed is associated with propofol. Propofol is known for its rapid onset and recovery properties, making it a common choice for anesthesia induction. Importantly, it has a relatively mild effect on SSEP signals compared to the other anesthetics listed, which is crucial for maintaining the integrity of intraoperative monitoring.

Isoflurane and halothane are volatile anesthetics that can significantly depress the SSEP response due to their effects on neuronal function and synaptic transmission, leading to reduced amplitude and altered latency of the SSEP waves. Etomidate, while beneficial for hemodynamic stability, can also affect SSEP responses, though its impact is generally less pronounced than that of isoflurane or halothane but still more than that of propofol.

Given the importance of maintaining SSEP integrity for monitoring purposes during surgery, the choice of propofol as an inductive agent is preferred in scenarios where minimal interference with neurophysiological monitoring is desired.