title: Comparison of anesthetic depth indexes based on thalamocortical local field potentials in rats.
abstract: BACKGROUND
  Local field potentials may allow a more precise analysis of the brain electrical activity than the electroencephalogram. In this study, local field potentials were recorded in the thalamocortical axis of rats to (i) compare the performance of several indexes of anesthetic depth and (ii) investigate the existence of thalamocortical correlated or disrupted activity during isoflurane steady-state anesthesia.
  
  
  METHODS
  Five rats chronically implanted with microelectrodes were used to record local field potentials in the primary somatosensory cortex and ventroposterolateral thalamic nuclei at six periods: before induction of anesthesia; in the last 5 min of randomized 20-min steady-state end-tidal 0.8, 1.1, 1.4, and 1.7% isoflurane concentrations; and after recovery. The approximate entropy, the index of consciousness, the spectral edge frequency, and the permutation entropy were estimated using epochs of 8 s. A correction factor for burst suppression was applied to the spectral edge frequency and to the permutation entropy. The correlation between the derived indexes and the end-tidal isoflurane was calculated and compared for the two studied brain regions indexes. Coherence analysis was also performed.
  
  
  RESULTS
  The burst suppression-corrected permutation entropy showed the highest correlation with the end-tidal isoflurane concentration, and a high coherence was obtained between the two studied areas.
  
  
  CONCLUSIONS
  The permutation entropy corrected with the classic burst suppression ratio is a promising alternative to other indexes of anesthetic depth. Furthermore, high coherence level of activity exists between the somatosensory cortical and thalamic regions, even at deep isoflurane stages.
authors.affiliation: Centro de Ciência Animal e Veterinária, Universidade de Trás-os-Montes e Alto Douro, Vila Real, Portugal. asilva@ibmc.up.pt
authors.forename: Aura
authors.initials: A
authors.lastname: Silva
authors.forename: Hélder
authors.initials: H
authors.lastname: Cardoso-Cruz
authors.forename: Francisco
authors.initials: F
authors.lastname: Silva
authors.forename: Vasco
authors.initials: V
authors.lastname: Galhardo
authors.forename: Luís
authors.initials: L
authors.lastname: Antunes
mesh_terms: D000758:Anesthesia; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D003243:Consciousness / Q000187:drug effects; D004569:Electroencephalography / Q000187:drug effects*; D004594:Electrophysiology; D019277:Entropy; D005071:Evoked Potentials / Q000502:physiology*; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D008839:Microelectrodes; D051381:Rats; D017207:Rats, Sprague-Dawley; D013788:Thalamus / Q000187:drug effects / Q000502:physiology*
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane