Monitoring of the responsiveness to noxious stimuli during sevoflurane mono-anaesthesia by using RIII reflex threshold and bispectral index.

ABSTRACT

BACKGROUND: We investigated the accuracy of the (normalized) RIII reflex threshold, the bispectral index (BIS), and the end-tidal sevoflurane concentration for predicting movement responses during mono-anaesthesia using sevoflurane. METHODS: Fourteen male subjects were included. Each received a sevoflurane mono-anaesthesia for which the end-tidal concentration was increased in steps of 0.2 vol% every 10 min. Every 5 min, the reactions to noxious stimuli (10 s trapezius squeeze and 30 s 80 mA tetanic stimulus) were tested. The administration of sevoflurane was halted after no movement reactions occurred for three concentration steps. RIII reflex threshold and BIS were recorded continually in all subjects. RESULTS: Thirteen subjects completed the study. The prediction probabilities for movement reactions to the noxious stimuli were 0.79 for the BIS, 0.91 for the RIII threshold, and 0.89 for the end-tidal sevoflurane concentration (PKDMACRO-Statistics BIS vs RIII, P<0.05; BIS vs C(sevo), P<0.05; RIII vs C(sevo), P>0.05). All population prediction probability values differed significantly from 0.5 (P<0.01, PKDMACRO). CONCLUSIONS: All three instruments can be used for a prediction of movement responses to a noxious stimulus under sevoflurane mono-anaesthesia with an accuracy exceeding prediction by chance. The accuracy of the BIS to predict these responses appears to be lower compared with the RIII reflex threshold or the end-tidal sevoflurane concentration.