Evidence of auditory processing during postoperative propofol sedation.
OBJECTIVE
Our aim was to characterize cerebral event-related responses, which index the detection of auditory stimuli during postoperative sedation.


METHODS
We monitored auditory event-related potentials (ERPs) before and after elective cardiac operation in 29 patients. Sedation levels, induced with propofol, were evaluated clinically with Ramsay score (RS).


RESULTS
During deep sedation (RS 6), patients could be categorized into 3 groups according to ERP responses evoked by a standard 'oddball' paradigm. In one group, there were no cortical responses indexing the detection of a sound (N100), another group showed clear responses, and the third group was characterized by a later P300a component which was taken to reflect orienting to a novel stimulus in adults who were awake. However, in deep sedation, P300a did not show behaviour characteristic to an orienting reaction. In moderate sedation (RS 4), all the patients showed a visible N100. Total sedative propofol dose, hemodynamics and the spontaneous electroencephalography (EEG) were not connected to the category of an individual's responses.


CONCLUSIONS
The results of our study suggest that the detection and automatic auditory information processing function during postoperative sedation, and may signal the individual stages of awakening in a sensitive way. In addition, the findings suggest a deficit in sensory memory function during sedation.
Department of Clinical Neurophysiology, Kuopio University Hospital, University of Kuopio, Kuopio, Finland. heidi.ypparila@kuh.fi
Heidi
H
Yppärilä
Jari
J
Karhu
Susanna
S
Westerén-Punnonen
Tadeusz
T
Musialowicz
Juhani
J
Partanen
D000161:Acoustic Stimulation; D004569:Electroencephalography; D005071:Evoked Potentials; D006993:Hypnotics and Sedatives; D011184:Postoperative Period; D015742:Propofol; D013903:Thoracic Surgery
D006993:Hypnotics and Sedatives; D015742:Propofol