SummaryMovement and haemodynamic responses to noxious stimuli during general anaesthesia are regarded as signs of nociception. We compared the Nociceptive Flexion Reflex Threshold (NFRT), Bispectral Index (BIS), Composite Variability Index (CVI), Noxious Stimulation Response Index (NSRI) and the calculated propofol ⁄ remifentanil effectcompartment concentrations (Ce) as predictors for such responses in 50 female subjects at laryngeal mask airway insertion and skin incision. Although the cerebral effect of hypnotics may be monitored using processed electroencephalography, no comparable monitor exists to measure nociception during general anaesthesia. In clinical practice, opioids are administered according to haemodynamic and movement responses to noxious stimuli [1].The correlation of such responses with the hypnotic depth as measured by the bispectral index (BIS) is relatively poor [2,3]. The composite variability index (CVI), which is derived from the BIS, may provide a better correlation and whereas promising results are presented in abstract form [4,5], no full research paper has yet been published.The nociceptive flexion reflex (NFR) is a polysynaptic spinal withdrawal reflex, which can be assessed by electromyography of the biceps femoris muscle

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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.

Probably because of the polysynaptic relay, the attenuation of the withdrawal reflex exceeds the attenuation of the H reflex. Sevoflurane produces a larger inhibitory effect on the H reflex than propofol, which confirms that the ventral horn is a more important target for volatile anesthetics, whereas effects of propofol on this site of action are rather limited. Our findings indirectly suggest for propofol a relatively stronger effect within the dorsal horn.

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