A measure of consciousness and memory during isoflurane administration: the coherent frequency.
The coherent frequency (CF) of the auditory evoked response (AER) is derived using auditory clicks presented at frequencies in the range 5-47 Hz. CF and psychological performance were measured while seven subjects breathed isoflurane in doses increasing from 0% to 0.2%, 0.4% and 0.8% end-tidal concentration and then decreasing to 0%. With increasing doses of isoflurane, CF decreased and there was a decrease in within-list recognition (WLR) and category recognition (CR) scores. There was a correlation between changes in CF and WLR (P < 0.05) and between CF and category recognition (CR) (P < 0.05). A painful stimulus given in conjunction with 0.4% isoflurane caused an increase in CF, WLR and CR in some subjects. This did not reach statistical significance for the group as a whole, apart from the short word interval scores in the WLR which indicated an increase in attention (P < 0.01). Subjects did not respond with 0.8% isoflurane, either before or after painful stimulation. Reduction of end-tidal isoflurane from 0.8% to 0% caused an increase in the CF and improved performance on the psychological tests. A category generation task on recovery showed no evidence of implicit learning of words presented in conjunction with 0.8% isoflurane.(ABSTRACT TRUNCATED AT 250 WORDS)
Munglani
R
R
Cambridge University Department of Anaesthesia, Addenbrooke's Hospital.
Andrade
J
J
Sapsford
D J
DJ
Baddeley
A
A
Jones
J G
JG
D000769:Anesthesia, Inhalation; D001364:Awareness / Q000187:drug effects; D003071:Cognition / Q000187:drug effects; D003243:Consciousness / Q000187:drug effects*; D005072:Evoked Potentials, Auditory / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006801:Humans; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D008568:Memory / Q000187:drug effects*; D011581:Psychological Tests; D013997:Time Factors
D007530:Isoflurane