Monitoring of the responsiveness to noxious stimuli during anaesthesia with propofol and remifentanil by using RIII reflex threshold and bispectral index

Abstract

Background: Movement responses are an important indicator of noxious perception in the unconscious state. To allow for a continual monitoring of the responsiveness to noxious stimuli during general anaesthesia, surrogate parameters are needed. Here we compare the performance of the bispectral index (BIS) and the RIII threshold in predicting reactions to noxious stimuli during anaesthesia with propofol and remifentanil.

Methods: Twenty male volunteers were included. The first 10 subjects received constant concentrations of propofol while remifentanil concentrations were increased stepwise. The other 10 subjects each received high propofol concentrations combined with different low remifentanil concentrations and also low propofol concentrations combined with different high remifentanil concentrations. In all subjects, the reactions to an 80 mA 30 s tetanic stimulus were tested every 5 min. BIS and RIII threshold were recorded continually in all subjects.

Results: Nineteen subjects completed the study. The population prediction probability for reactions to the noxious stimuli amounted to 0.86 for the BIS and to 0.84 for the RIII threshold in the first 10 subjects (P>0.05, PKDMACRO). In the other nine subjects, the prediction probabilities amounted to 0.64 for the BIS and to 0.77 for the RIII threshold (P<0.05, PKDMACRO). All population prediction probability values differed significantly from 0.5 (P<0.01, PKDMACRO).

Conclusions: RIII threshold and BIS are both influenced dose-dependently by remifentanil at those concentrations that suppress reactions to noxious stimuli. The susceptibility of the parameters to remifentanil concentration seems to be of a similar quality. Under different ratios of propofol and remifentanil concentrations, the RIII threshold correlates with non-responsiveness better than the BIS.