Comparison of anesthetic depth indexes based on thalamocortical local field potentials in rats.
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.
Silva
Aura
A
Centro de Ciência Animal e Veterinária, Universidade de Trás-os-Montes e Alto Douro, Vila Real, Portugal. asilva@ibmc.up.pt
Cardoso-Cruz
Hélder
H
Silva
Francisco
F
Galhardo
Vasco
V
Antunes
Luís
L
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*
D018685:Anesthetics, Inhalation; D007530:Isoflurane