An accurate dosage of anesthetics during surgery is important. Usually this is achieved through close observation of the patient, but a new monitor (CSM-monitor) can measure the level of anesthesia more closely.

In obese patients dosage of drugs is difficult due to the change in body composition. The CSM-monitor may provide a more accurate dosage of propofol (an anesthetic agent) during surgery, and as a consequence of that, also reduce the postoperative need for analgesics.

Main objective: To optimise propofol dosing in obese patients undergoing hysterectomy.

Main hypothesis: Monitoring the depth of anesthesia using the CSM-monitor reduces time to opening eyes in obese patients after hysterectomy in propofol anesthesia.

Secondary hypotheses: CSM-monitoring reduce propofol dose in obese patients undergoing hysterectomy. Patients with a high CSM-level during hysterectomy have higher postoperative consumption of analgesics. Supplementary, an algorithm for the dose of propofol that most frequently results in a CSM-level between 40 and 60 is calculated.

Inclusion Criteria:

• Elective abdominal non-laparoscopic hysterectomy
• Age > 18 years
• ASA physical status I-III
• Body Mass Index 30 or above

Exclusion Criteria:

• Allergic towards propofol
• Daily consumption of benzodiazepines (more than at nighttime), opioids or amphetamine preoperatively.
• Disease with expected EEG-abnormality or impaired auditory function: Epilepsy, deafness, previous neurosurgery, previous or actual neurologic disease with neurologic deficit.