BJA Advance Access originally published online on April 4, 2006
British Journal of Anaesthesia 2006 96(6):742-746; doi:10.1093/bja/ael081
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Level of consciousness affects the excitability of spinal motor neurones during propofol sedation in humans
Department of Anesthesiology, Faculty of Medicine, University of the Ryukyus Okinawa, Japan
*Corresponding author: Department of Anesthesiology, Faculty of Medicine, University of the Ryukyus, 207 Uehara, Nishihara, Okinawa, 903-0125, Japan. E-mail: mnb-shk{at}ryukyu.ne.jp
Background. To investigate the relationship between the depression of spinal motor neuronal excitability and the sedative level induced by propofol infusion, we simultaneously analysed the suppressive effect of propofol on the F wave and the sedative level during propofol infusion.
Methods. After spinal anaesthesia, sedation was achieved using a propofol target-controlled infusion (TCI) system to achieve a score of 4 on the Wilson sedation scale. The excitability of spinal motor neurones was determined by measuring the left median nerve F wave. F-wave persistence and the F/M ratio were recorded at pre-sedation as the control, during sedation, at arousal by mild physical stimulation and at post-sedation.
Results. Wilson sedation scores increased significantly corresponding to the increase in the target propofol concentration (Cpt), and a Cpt-producing Wilson sedation scale 4 ranged between 1.2 and 1.8 µg ml–1. The F-wave persistence and F/M ratio before propofol infusion were 80.7 (8.6)% and 9.5 (3.9)%, respectively. At Wilson sedation scale 4, F-wave persistence and F/M ratio were 17.6 (12.8)% (0–37.5%) and 4.3 (4.1)%, and, at return of consciousness by mild physical stimulation, significantly increased to 71.3 (7.9)% and 10.0 (5.0)%, respectively.
Conclusion. We demonstrated that the excitability of spinal motor neurones was suppressed during sedation by propofol TCI, but this suppressive effect vanished at return of consciousness by mild physical stimulation even at a constant Cpt. Our data suggested that the effect of propofol on the excitability of spinal motor neurones might be affected by consciousness level rather than propofol Cpt in humans.
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