Effect of Ketamine on Intraoperative Motor Evoked Potentials

Spinal surgeries continue to increase in frequency and complexity. An important safety protocol is the use of intraoperative motor evoked potentials (MEP) to monitor the integrity and function of the spinal cord and alert the surgeon of any potential injury. Transcranial electric motor evoked potentials stimulate the motor cortex and produce a myogenic response. This modality can assess the function of all pathways including the motor cortex, the lateral corticospinal tracts, the function of the alpha motor neurons, and peripheral nerves.

Various anesthetic agents can impact the critical parameters of MEPs. Inhaled volatile anesthetics and nitrous oxide are highly suppressive in a dose-dependent manner decreasing the amplitude of the myogenic response and prolonging the latency. Propofol is also suppressive of MEPs, although high quality data can still be obtained at clinically relevant doses for anesthesia. For this reason, most anesthesiologists will use propofol as the backbone of any anesthetic that involves neurophysiologic monitoring.

Because spine surgeries are exceptionally painful, anesthesiologists will often incorporate adjuncts that can decrease pain and postoperative opioid usage. The effect of these adjuncts on intraoperative evoked potentials is incompletely described and important work remains to detail these effects.

Ketamine, a phencyclidine derivative that is an NMDA receptor antagonist, is a widely used adjunct anesthetic due to its analgesic and hypnotic properties during spine surgeries. Ketamine has shown significant opioid-sparing and analgesic benefits when used in patients undergoing spine surgery.

Intraoperative neuromonitoring (IONM), including motor evoked potentials (MEP), are increasingly used during spinal surgeries to help identify potentially reversible injury to neural structures.