Noxious stimuli do not modify myogenic motor evoked potentials by electrical stimulation during anesthesia with propofol-based anesthesia

Abstract

Purpose: To investigate whether motor evoked potentials (MEP) to transcranial electrical stimulation under constant blood propofol concentration are affected by the arousing effect of surgical noxious stimuli. Methods: Twenty patients who underwent elective spinal surgery were studied. Patients were anesthetized with 50% nitrous oxide in oxygen, fentanyl, and propofol to maintain the bispectral index (BIS) score around 50. MEP in response to a multipulse transcranial electrical stimulation at stimulus sites of C3-C4 were recorded over the right abductor pollicis brevis muscle. Changes of peak-to-peak amplitude and onset latency of MEP, BIS score before and after surgical stimuli were evaluated. Propofol plasma concentration was measured at the same time points. Results: Both MEP amplitude and latency did not change significantly after surgical stimuli although BIS increased significantly (48 ± 6 to 58 ± 5; P < 0.05). Plasma propofol concentration was maintained at the same level between the two measurement points (3.3 ± 0.7 to 3.3 ± 0.7 μg·mL-1). There was no relation between BIS change and changes of MEP amplitude and latency, and propofol plasma concentration. Conclusion: MEP to the transcranial electrical stimulation under a constant and clinically appropriate blood ropofol concentration are not affected by surgical noxious stimuli.