This prospective randomized clinical trial evaluates the effects of a monitor-guided opioid analgesia during general anesthesia. To date no standard-monitoring device exists to specifically reflect the analgesic component of general anesthesia. Quality and safety of general anesthesia are of major clinical importance and should be improved by limiting the opioid analgesic's dosage to the minimum amount needed. The study compares the effects of monitoring nociception during general anesthesia with different innovative techniques in comparison to routine clinical practice.

This prospective randomized clinical study aims to investigate the effects of a monitor-guided opioid analgesia during general anesthesia by different monitoring systems in comparison to routine clinical practice. Many surgical procedures require general anesthesia. The main components of general anesthesia are hypnosis and analgesia, and anesthesiologists usually combine a hypnotic drug with an opioid analgesic.

Until today, however, there is no standard-monitoring of nociception to specifically reflect the analgesic component of general anesthesia. In clinical practice the opioid dosage is chosen by clinical judgment of the attending anesthesiologist based upon changes of heart rate, blood pressure, pupil size, lacrimation and sweating of the patient.

On the one hand, underdosage of opioids can cause nociception leading to an increased sympathetic tone, increase of plasma levels of stress hormones, nociceptive movements as well as increase postoperative pain. On the other hand, overdosage of opioids can lead to drug side effects such as nausea and vomiting, hemodynamic instability, an increase in recovery times, immunosuppression and an increase in postoperative pain by opioid-induced-hyperalgesia. Quality and safety of general anesthesia are of major clinical importance and can be improved by limiting the administration of opioid analgesics to the optimal individual dose needed. In the last years, different analgesia monitoring devices have been developed for monitoring nociception. The present study evaluates the effects of the administration of opioids during general anesthesia guided by three different monitoring systems in comparison to routine clinical practice. All patients will receive general anesthesia with propofol guided by bispectral index (BIS) with a target of BIS values between 40 and 60. Opioid administration will be guided by one of three analgesic monitoring devices or the interpretation of clinical signs by the attending anesthesiologist in the control group. After institutional approval by the Ethics committee of the Medical Board of the City of Hamburg, Germany and obtaining patients' written informed consent we randomize elective patients with major abdominal surgery for open radical prostatectomy into one of four treatment groups.

Inclusion Criteria:

• Radical open abdominal prostatectomy scheduled in the operation theater where the study is conducted
• > 18 years

Exclusion Criteria:

• Chronic opioid therapy
• Beta blocker and digitalis therapy
• Eye disease with affection of pupil reactivity
• Pacemaker therapy
• Higher degrees of cardiac arrhythmias, e.g. atrial fibrillation
• Pre-operative medication with steroids

All data will be anonymized before publication.

Participants are not informed about the group assignement (intervention takes place in general anesthesia). Outcome assessors are persons without knowledge on former treatment in intervention/control group.