Dose-dependent effects of propofol on the central processing of thermal pain.
BACKGROUND
Anatomic and physiologic data show that multiple regions of the forebrain are activated by pain. However, the effect of anesthetic level on nociceptive input to these regions is not well understood.


METHODS
The authors used positron emission tomography to measure the effect of various concentrations of propofol on pain-evoked changes in regional cerebral blood flow. Fifteen volunteers were scanned while warm and painful heat stimuli were presented to the volar forearm using a contact thermode during administration of target propofol concentrations of 0.0 microg/ml (alert control), 0.5 microg/ml (mild sedation), 1.5 microg/ml (moderate sedation), and 3.5 microg/ml (unconsciousness).


RESULTS
During the 0.5-microg/ml target propofol concentration (mild sedation), the subjects' pain ratings increased relative to the alert control condition; correspondingly, pain-evoked regional cerebral blood flow increased in the thalamus and the anterior cingulate cortex. In contrast, when subjects lost consciousness (3.5 microg/ml), pain-evoked responses in the thalamus and the anterior cingulate cortex were no longer observed, whereas significant pain-evoked activation remained in the insular cortex.


CONCLUSIONS
These data show that propofol has a dose-dependent effect on thalamocortical transfer of nociceptive information but that some pain-evoked cortical activity remains after loss of consciousness.
Hofbauer
Robert K
RK
Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada.
Fiset
Pierre
P
Plourde
Gilles
G
Backman
Steven B
SB
Bushnell
M Catherine
MC
D000328:Adult; D018686:Anesthetics, Intravenous / Q000008:administration & dosage / Q000627:therapeutic use*; D001794:Blood Pressure; D001921:Brain / Q000000981:diagnostic imaging / Q000187:drug effects; D002560:Cerebrovascular Circulation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D006358:Hot Temperature; D006801:Humans; D008297:Male; D010146:Pain / Q000209:etiology / Q000517:prevention & control*; D015742:Propofol / Q000008:administration & dosage / Q000627:therapeutic use*; D011859:Radiography; D014055:Tomography, Emission-Computed
D018686:Anesthetics, Intravenous; D015742:Propofol