Effect of Ketamine and Dexmedetomidine as Adjuvant to Total Intravenous Anesthesia on Intraoperative Cranial Nerve Monitoring in the Patients Undergoing Posterior Fossa Craniotomies-A Randomized Quadruple Blind Placebo-Controlled Study.

 Total intravenous anesthesia (TIVA) is used during surgery with intraoperative neurophysiological monitoring. Addition of adjuvant may minimize suppression of potentials by reducing doses of propofol. We studied the effect of addition of ketamine or dexmedetomidine to propofol-fentanyl-based TIVA on corticobulbar motor evoked potential (CoMEP) in patients undergoing posterior fossa surgeries.  Forty-two patients were assigned to three groups (  = 14 each), Group S-saline, Group D-dexmedetomidine (0.25 μg/kg/h), and Group K-ketamine (0.25 mg/kg/h). Patients received propofol and fentanyl infusions along with study drugs. CoMEPs were recorded from muscles innervated by cranial nerves bilaterally at predefined intervals (T , T , T , T , and T ). Effect on amplitude and latency of CoMEPs was assessed.  A significant fall in CoMEP amplitude was observed across all analyzed muscles at time T and T in saline and dexmedetomidine group as compared with ketamine group, -value less than 0.05. A significant increase in latency was observed at T4 and T5 among groups ( -value, D vs. K = 0.239, D vs. S = 0.123, and K vs. S = 0.001).  Both ketamine and dexmedetomidine provide and allow effective recording of CoMEPs. Ketamine emerges as a better agent especially when prolonged surgical duration is expected as even propofol-fentanyl-based TIVA adversely affects CoMEPs when used for long duration.