Dexmedetomidine versus sevoflurane as adjuncts to propofol-fentanyl anesthesia during major spine surgery with somatosensory and motor evoked potential monitoring: a randomized controlled trial

Background: Intraoperative neurophysiological monitoring (IONM) reduces neurological risk during major spine surgery. Total intravenous anesthesia (TIVA) is generally preferred for IONM; however, the comparative effects of dexmedetomidine and volatile adjuncts on evoked potential (EP) monitoring during propofol-based anesthesia remain inadequately characterized.Methods: This prospective randomized trial enrolled 135 adults undergoing spinal fusion for idiopathic scoliosis. Patients were allocated to propofol-fentanyl TIVA (Group A), propofol-fentanyl-dexmedetomidine anesthesia (Group B), or propofol-fentanyl-sevoflurane (Group C). The primary outcome was clinically significant somatosensory evoked potential (SSEP) and motor evoked potential (MEP) change, defined as > 50% reduction in amplitude and/or > 10% prolongation in latency from baseline. Secondary outcomes included EP parameters, anesthetic consumption, hemodynamics, bleeding, surgical field quality, emergence, adverse events, and postoperative outcomes.Results: Dexmedetomidine did not significantly affect SSEP or MEP monitoring compared with control. Sevoflurane produced dose-dependent reductions in SSEP and MEP amplitudes (adjusted odds ratio, 4.82 per 0.1 minimum alveolar concentration [MAC]; P = 0.006). Dexmedetomidine reduced propofol consumption by 25.9% and fentanyl consumption by 57.7% and was associated with the lowest intraoperative blood loss (552 ± 171 ml). Emergence was fastest with sevoflurane and slowest with dexmedetomidine. No neurological deficits occurred. Post hoc analyses showed no significant differences in postoperative pain scores, with lower postoperative opioid consumption and shorter time to ambulation observed with dexmedetomidine.Conclusions: Dexmedetomidine preserves EP amplitude and latency while reducing anesthetic requirements and improving surgical conditions. In contrast, sevoflurane produced dose-dependent EP suppression, even at sub-MAC concentrations. These findings suggest that dexmedetomidine may be a suitable adjunct for anesthesia that requires neuromonitoring; however, the hypothesis-generating observations warrant further investigation.