Spinal anaesthesia indirectly depresses cortical activity associated with electrical stimulation of the reticular formation.
BACKGROUND
Neuraxial blockade reduces the requirements for sedation and general anaesthesia. We investigated whether lidocaine spinal anaesthesia affected cortical activity as determined by EEG desynchronization that occurs following electrical stimulation of the midbrain reticular formation (MRF).


METHODS
Six goats were anaesthetized with isoflurane, and cervical laminectomy performed to permit spinal application of lidocaine. The EEG was recorded before, during and after focal electrical stimulation (0.1, 0.2, 0.3 and 0.4 mA) in the MRF while keeping the isoflurane concentration constant.


RESULTS
During lidocaine spinal anaesthesia, the spectral edge frequency (SEF) after MRF electrical stimulation (13.6 (SD 1.0) Hz, averaged across all stimulus currents) was less than the SEF during control and recovery periods (18.6 (3.6) Hz and 17.2 (2.2) Hz, respectively; P<0.05). Bispectral index values were similarly affected: 69 (10) at control compared with 55 (6) during the spinal block (P<0.05).


CONCLUSIONS
These results suggest that lidocaine spinal anaesthesia blocks ascending somatosensory transmission to mildly depress the excitability of reticulo-thalamo-cortical arousal mechanisms.
Antognini
J F
JF
Department of Anesthesiology and Pain Medicine and Section of Neurobiology, Physiology and Behavior, University of California, Davis, CA 95616, USA. jfantognini@ucdavis.edu
Jinks
S L
SL
Atherley
R
R
Clayton
C
C
Carstens
E
E
D000775:Anesthesia, Spinal; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects* / Q000502:physiology; D004558:Electric Stimulation; D004569:Electroencephalography / Q000187:drug effects; D005260:Female; D006041:Goats; D008012:Lidocaine / Q000494:pharmacology; D012154:Reticular Formation / Q000502:physiology*
D000779:Anesthetics, Local; D008012:Lidocaine