The aim of this prospective randomized study was to evaluate the ability of the new Analgesia Nociception Index ANI, derived by heart rate variability, to detect painful stimulation during either propofol or sevoflurane anesthesia and changing remifentanil concentrations.

Monitoring Antinociception during general anesthesia is still a big challenge in the field and has not become clinical routine yet. Recently, for the Surgical Pleth Index SPI a benefit for the patient in terms of reduction of remifentanil use, less unwanted effects and shorter recovery from anesthesia was reported. However, there are new variables like the ANI that are developed to measure antinociception during anesthesia.

In the present study the investigators want to evaluate, whether ANI detects a painful tetanic stimulus during general anesthesia using propofol or sevoflurane and different concentrations of remifentanil.

Inclusion Criteria:

• age between 18- 65 years,
• ASA physical status I or II,
• elective surgery in general anesthesia planned,
• written informed consent

Exclusion Criteria:

• pregnancy,
• history of cardiac arrhythmia,
• presents of any neuromuscular or neurologic disease,
• use of CNS-active medication or abuse of alcohol/illicit drugs -

Patients scheduled for elective surgery in general anesthesia