The primary objective of this study is to investigate the influence of a standardized noxious stimulus on the ANI, SPI and hemodynamic parameters during standard propofol and sufentanil TCI and to see if the ANI and SPI are predictive of a hemodynamic reaction.

In addition the investigators compare the performance of ANI and SPI against one another as well as investigate if ANI or SPI can be used to find the ideal CeSUF for a given patient.

During general anesthesia hypnosis can be monitored routinely using EEG derivates like Bispectral index (BIS), entropy,.… However, monitoring analgesia or more precisely the nociceptive-antinociceptive (analgetic) balance during anesthesia proved more difficult. Clinical signs such as heart rate (tachycardia) or blood pressure (hypertension) are usually observed and used to assess nociception and a patient's autonomic unbalance. During general anesthesia administration of opioids like sufentanil and remifentanil decrease the ANS reactivity to noxious stimulation. Recently two variables based on standard anesthesia monitor equipment have been introduced into clinical practice: the Analgesia Nociception Index (ANI), derived from analysis of the small beat-to-beat oscillations of the heart rate during respiration, the heart rate variability (HRV), and the Surgical Pleth Index (SPI), calculated from the plethysmographic amplitude and heart beat interval.

Inclusion Criteria:

• Male
• non-pregnant female participants
• ASA II-III
• >18-65 years
• Weight not exceeding 30% under or above ideal body weight
• Elective intracranial surgery or circumcision.

Exclusion Criteria:

• Use concurrent opioid containing drugs
• Use of any autonomic nervous system altering drugs
• History of opioid or alcohol abuse
• Hepatic, renal, metabolic, neuromuscular or cardiovascular disease
• Known allergies to anesthestetic / analgesic drugs
• Use of a peripheral nerve block, penile block