The investigators hypothesize that the noise level in the operating theatre influences the patients' requirements of anesthetics. Study subject are patients undergoing abdominal surgery in combined general and epidural anesthesia. Analgesia is maintained by epidural injections of sufentanil and ropivacaine whereas general anesthesia is maintained using the inhalational anesthetic desflurane. Desflurane requirements are adjusted using neuromonitoring (BIS-Index). Intraoperative noise levels are recorded. Patients are randomized to receive hearing protections or not.
All patients receive standardized anesthesia and monitoring according to the usual clinical care in the department. Placement of epidural catheters takes place before induction of general anesthesia. Thereafter, 10 ml ropivacaine 0.3% with 10 µg sufentanil are administered epidurally every 60 min to induce and maintain analgesia during surgery.
Following induction of general anesthesia and tracheal Intubation, intraoperative hypnosis is maintained using desflurane.
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Exclusion Criteria: