title: The influence of depth of anesthesia on motor evoked potential response during awake craniotomy.
abstract: OBJECTIVE Motor evoked potentials (MEPs) are a critical indicator for monitoring motor function during neurological surgery. In this study, the influence of depth of anesthesia on MEP response was assessed. METHODS Twenty-eight patients with brain tumors who underwent awake craniotomy were included in this study. From a state of deep anesthesia until the awake state, MEP amplitude and latency were measured using 5-train electrical bipolar stimulations on the same site of the precentral gyrus each minute during the surgery. The depth of anesthesia was evaluated using the bispectral index (BIS). BIS levels were classified into 7 stages: < 40, and from 40 to 100 in groups of 10 each. MEP amplitude and latency of each stage were compared. The deviation of the MEP measurements, which was defined as a fluctuation from the average in every BIS stage, was also considered. RESULTS A total of 865 MEP waves in 28 cases were evaluated in this study. MEP amplitude was increased and latency was decreased in accordance with the increases in BIS level. The average MEP amplitudes in the > 90 BIS level was approximately 10 times higher than those in the < 40 BIS level. Furthermore, the average MEP latencies in the > 90 BIS level were 1.5-3.1 msec shorter than those in the < 60 BIS level. The deviation of measured MEP amplitudes in the > 90 BIS level was significantly stabilized in comparison with that in the < 60 BIS level. CONCLUSIONS MEP amplitude and latency were closely correlated with depth of anesthesia. In addition, the deviation in MEP amplitude was also correlated with depth of anesthesia, which was smaller during awake surgery (high BIS level) than during deep anesthesia. Therefore, MEP measurement would be more reliable in the awake state than under deep anesthesia.
authors.affiliation: Departments of 1 Neurosurgery and.
authors.forename: Shunya
authors.initials: S
authors.lastname: Ohtaki
authors.affiliation: Departments of 1 Neurosurgery and.
authors.forename: Yukinori
authors.initials: Y
authors.lastname: Akiyama
authors.affiliation: Departments of 1 Neurosurgery and.
authors.forename: Aya
authors.initials: A
authors.lastname: Kanno
authors.affiliation: Departments of 1 Neurosurgery and.
authors.forename: Shouhei
authors.initials: S
authors.lastname: Noshiro
authors.affiliation: Anesthesiology, Sapporo Medical University School of Medicine, Sapporo, Hokkaido, Japan.
authors.forename: Tomo
authors.initials: T
authors.lastname: Hayase
authors.affiliation: Anesthesiology, Sapporo Medical University School of Medicine, Sapporo, Hokkaido, Japan.
authors.forename: Michiaki
authors.initials: M
authors.lastname: Yamakage
authors.affiliation: Departments of 1 Neurosurgery and.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Mikuni
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000758:Anesthesia; D000777:Anesthetics / Q000008:administration & dosage*; D001932:Brain Neoplasms / Q000503:physiopathology / Q000601:surgery; D003399:Craniotomy; D004569:Electroencephalography; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000187:drug effects*; D005260:Female; D006801:Humans; D064795:Intraoperative Neurophysiological Monitoring; D008297:Male; D008875:Middle Aged; D014851:Wakefulness; D055815:Young Adult
chemical_list: D000777:Anesthetics
keywords: BIS = bispectral index; EEG = electroencephalography; EMG = electromyography; GABA = γ-aminobutyric acid; MEP = motor evoked potential; anesthesia depth; bispectral index; diagnostic and operative techniques; motor evoked potential