Influence of Ketamine on Motor Evoked Potentials During Brain and Spine Surgery: A Scoping Review of Clinical Evidence

Abstract Ketamine is an evolving anesthetic adjunct in neurosurgery for its potential to improve motor evoked potential (MEP) monitoring; however, the evidence regarding its efficacy remains contradictory due to variability in the dosing regimens used in clinical practice, concurrent anesthetics used along with it, the timing of stimulation, and the stimulation parameters used to elicit the MEPs. This scoping review maps the evidence available on ketamine's impact on intraoperative MEPs across various neurosurgical settings. Following the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews) guidelines, a comprehensive search was conducted across PubMed, Scopus, Cochrane Library, and Web of Science for studies published till July 15, 2025. Randomized controlled trials, cohort studies, and case reports evaluating ketamine's effects on intraoperative MEPs were included. Data on study design, population, dosing regimens, stimulation parameters, and MEP amplitude/latency changes were extracted. Thirteen studies were included. Seven demonstrated increased MEP amplitude, four showed no significant change, and two reported transient suppression, primarily associated with high bolus doses. Augmentation effects were consistently observed with low-dose or continuous infusions, particularly in cervical spine or pediatric surgeries. High bolus doses of ketamine may cause transient signal suppression, whereas low-dose or infusion-based regimens typically enhance MEP amplitude. Despite encouraging findings, definitive conclusions are limited by study heterogeneity, small sample sizes, and nonstandardized dosing. The evidence gap in this area is the lack of data utilizing the target-controlled infusion pumps to correlate with the amplitude of the MEPs with the serum levels of ketamine to understand the optimal dosing.