The Changes of Reaction Time to Visual and Auditory Stimulations during Propofol Administration for Conscious Sedation

Noh, Gyu Jeong; Jeon, Woo Jae

Abstract

BACKGROUND: As the clinical-end point is not clear-cut in conscious sedation, there are no objective and feedback-providing methods to assess the depth of sedation within the levels appropriate for conscious sedation.
METHODS
The investigation was carried out on 19 ASA PS 1 patients. The authors developed a system to measure the reaction time to visual (red colored flash, 40 lux for 30 msec) and auditory (beep, 1,000 Hz, 67.5 dB for 30 msec) stimulations. The authors confirmed the beeps to be audible to all the patients before the test began. When they perceived a visual or auditory stimulation, the authors instructed the patients to signal by pushing a button as soon as possible. The reaction time was defined as the time from the beginning of stimulation to the push of a button. The patients were gradually sedated with propofol TCI. The authors measured the visual and auditory reaction time and BIS after every 0.1 microgram/ml increment of the effect site concentration of propofol.
RESULTS
As the effect site concentration of propofol increased, the reaction time to visual and auditory stimulations tended to be prolonged (P < 0.0001, respectively). The estimate was 409 and 498, respectively, which means the slope a in y = ax; x means unit change of the effect site concentration of propofol; y means the estimated values of the reaction time. The BIS values at loss of response to visual and auditory stimulations were 86 +/- 7 and 78 +/- 7 (mean +/- SD).
CONCLUSIONS
The responses to visual and auditory stimulations were prolonged and ultimately abolished as the effect site concentration of propofol increased. The loss of response to visual stimulations preceded the loss of response to auditory stimulations. The BIS values at loss of responses to visual and auditory stimulations suggested light and moderate sedation, respectively.