title: Effects of isoflurane and propofol on cortical somatosensory evoked potentials during comparable depth of anaesthesia as guided by bispectral index.
abstract: BACKGROUND
  The aim of this study was to determine if propofol caused less suppression of cortical somatosensory evoked potentials (SSEPs) during spine surgery compared with isoflurane during comparable depth of anaesthesia as guided by bispectral index (BIS) measurements.
  
  
  METHODS
  This was a randomized controlled trial of propofol and isoflurane involving 60 patients undergoing elective spine surgery. BIS monitoring was used to guide a consistent and comparable depth of anaesthesia, the index was maintained at between 40 and 50 during anaesthesia. The cortical SSEP P40-N50 peak-to-peak amplitude and latency time to the P40 peak were measured before induction of anaesthesia, after induction of anaesthesia, at the start of skin incision, at the start of pedicle screw insertion and at the start of rod insertion, by a neurophysiologist blinded to drug allocation.
  
  
  RESULTS
  Both propofol and isoflurane decreased SSEP amplitude and increased latency during the course of anaesthesia. After achieving a comparable depth of anaesthesia, the SSEP amplitude was significantly lower with isoflurane, 1.5 (1.0) vs 2.4 (1.4) muV (P=0.005). Latency was significantly longer with isoflurane, 39.5 (3.9) vs 37.3 (3.1) ms (P=0.024). Isoflurane was associated with greater variability of SSEP amplitude during the course of anaesthesia and surgery, coefficient of variation 35.4 (18.0) vs 21.2 (10.2)% (P=0.008).
  
  
  CONCLUSIONS
  Propofol anaesthesia caused less suppression of the cortical SSEP, with better preservation of SSEP amplitude, and less variability at an equivalent depth of anaesthesia.
authors.affiliation: Department of Anaesthesia, National University Hospital, 5 Lower Kent Ridge Road, Singapore 119074.
authors.forename: E H C
authors.initials: EH
authors.lastname: Liu
authors.forename: H K
authors.initials: HK
authors.lastname: Wong
authors.forename: C P
authors.initials: CP
authors.lastname: Chia
authors.forename: H J
authors.initials: HJ
authors.lastname: Lim
authors.forename: Z Y
authors.initials: ZY
authors.lastname: Chen
authors.forename: T L
authors.initials: TL
authors.lastname: Lee
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D002648:Child; D004569:Electroencephalography / Q000187:drug effects; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects*; D005260:Female; D006801:Humans; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods; D015742:Propofol / Q000494:pharmacology*; D011930:Reaction Time / Q000187:drug effects; D016037:Single-Blind Method; D013116:Spinal Cord / Q000503:physiopathology; D013131:Spine / Q000601:surgery
chemical_list: D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D007530:Isoflurane; D015742:Propofol