Multi-level approach to anaesthetic effects produced by sevoflurane or propofol in humans: 1. BIS and blink reflex
1 Department of Anaesthesia, Radboud University Nijmegen Medical Centre, Geert Grooteplein 10, 6500 HB Nijmegen, The Netherlands
2 Department of Anaesthesia and Heymans Institute of Pharmacology, Ghent University, Ghent, Belgium
3 Department of Clinical Neurophysiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
* Corresponding author. E-mail: j.mourisse{at}anes.umcn.nl
Background: The relative roles of forebrain and brainstem in producing adequate anaesthesia are unclear.
Methods: We simultaneously analysed the effects of sevoflurane (Group S; n = 18) or propofol (Group P; n = 29) on the bispectral index (BIS) and the first component of the blink reflex (R1). The dose of anaesthetic agent was increased until loss of blink reflex. After discontinuation and reappearance of blink reflex activity, the amount was increased again. The area under curve R1 (area-R1) of the electromyogram of the orbicularis oculi muscle after electrical stimulation of the supraorbital nerve was measured. Using a sigmoid Emax model and a first-order rate constant ke0, we characterized the doseresponse relationships for BIS and area-R1.
Results: Concentration-dependent depression of BIS and area-R1 was adequately modelled. The concentration that causes an effect midway between minimum and maximum (EC50) for area-R1 was smaller than EC50 for BIS in both groups [0.34 (0.19) vs 1.29 (0.19) vol% and 1.78 (0.65) vs 2.69 (0.67) µg ml1; mean (SD)]. At doses of sevoflurane and propofol with equivalent depression of BIS, sevoflurane depressed area-R1 more than propofol. The ke0 for area-R1 was about half that for BIS in both groups: 0.24 (0.190.29) vs 0.48 (0.380.60) min1 for Group S; 0.28 (0.230.34) vs 0.46 (0.400.54) min1 for Group P, geometric mean (95% CI).
Conclusions: The blink reflex (brainstem function) is more sensitive to sevoflurane or propofol than BIS (forebrain function). Sevoflurane suppresses the blink reflex more than propofol. Different ke0s for blink reflex vs BIS indicate different effect sites.
Keywords: anaesthetic volatile; sevoflurane; anaesthetics i.v., propofol; monitoring, bispectral index; monitoring, depth of anaesthesia
This article is accompanied by Editorial I.
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