The aim of the present prospective randomized study was to challenge the ability of SSI to detect painful stimulation during sevoflurane - remifentanil anesthesia.

General anesthesia can be considered as a combination of hypnosis, antinociception and immobility. Whereas monitoring of depth of hypnosis, and muscle relaxation can be regarded as accepted, determination of the nociception is based on clinical signs like somatic or autonomic responses.

Recently, the multivariate surgical stress index (SSI)has been demonstrated to correlate with surgical stress intensity. Thus, SSI might be a useful variable to adjust analgesic drug administration in individual patients.

We want to investigate whether SSI is able to indicate nociception following standardized noxious stimulation during balanced sevoflurane - remifentanil anesthesia.

Inclusion Criteria:

• age between 18 and 65 years
• ASA physical status 1-2
• elective surgery in general anesthesia of 1 to 2 hours
• written informed consent

Exclusion Criteria:

• pregnancy
• history of cardiac arrhythmia
• presence of any neuromuscular or neurological disease
• use of CNS-active medication or abuse of alcohol or illicit drugs