 Until today there is no standard-monitoring to specifically reflect the analgesic component of general anesthesia. Quality and safety of general anesthesia are of major clinical importance and can be improved by limiting the administration of opioid analgesics to the minimum dose needed. This study therefore examines the quality of three different monitoring techniques PhysioDoloris, MetroDoloris, Lille, France, SPI Surgical Plethysmographic Index, GE Healthcare, Helsinki, Finland and AlgiScan, IDMed, Marseille, France in assessing the level of analgesia during general anesthesia. Therefore a standardized painful stimulus is applied under different levels of analgesic drugs. The monitors indices are compared to clinical signs such as an increase in heart rate and blood pressure. 