This protocol describes a total of three studies that are intrinsically linked. It does therefore have three titels.

INTERVENTION: Trade Name: LENOXe 100% (V/V) Product Name: Xenon Pharmaceutical Form: Inhalation gas INN or Proposed INN: Xenon Concentration unit: % (V/V) percent volume/volume Concentration type: equal Concentration number: 100‐ Product Name: Sevoflurane Pharmaceutical Form: Inhalation gas INN or Proposed INN: SEVOFLURANE CAS Number: 28523866 Concentration unit: % (V/V) percent volume/volume Concentration type: range Concentration number: 0.8‐1.1 Product Name: Dexamethason Pharmaceutical Form: Intravenous infusion INN or Proposed INN: DEXAMETHASONE CAS Number: 50022 Concentration unit: mg milligram(s) Concentration number: 4‐ Pharmaceutical form of the placebo: Intravenous infusion Route of administration of the placebo: Intravenous use Product Name: Ondansetron Pharmaceutical Form: Intravenous infusion INN or Proposed INN: ONDANSETRON CAS Number: 116002701 Concentration unit: mg milligram(s) Concentration type: equal Concentration number: 4‐ Pharmaceutical form of the placebo: Intravenous infusion Route of administration of the placebo: Intravenous use CONDITION: 1. The effect of xenon and sevoflurane on depth of hypnosis monitors when titrated to standard anesthesia parameter. 2. The efficacy of dexamethasone for prevention of PONV after xenon or sevoflurane. 3. Ondansetron as rescue for the treatment of established PONV after xenon or sevoflurane. PRIMARY OUTCOME: Main Objective: 1. To compare the effect of xenon or sevoflurane on the depth of hypnosis as assessed by the Bispectral Index (BIS) and the Composite Auditory Evoked Potential Index (cAAI) when titrated according to standard clinical parameter.; 2. To demonstrate that dexamethasone prevents PONV equally well after xenon or sevoflurane.; 3. To determine the onset‐time of ondansetron when used as rescue medication for postoperative nausea and vomiting.; Primary end point(s): 1. The average depths of hypnosis as assessed by the BIS and the cAAI between skin incision and start of closure.; 2. Postoperative nausea as assessed by a verbal rating scale (VRS) ranging between 0 and 10 after anaesthesia at 5, 10, 15, 30, 45, 60, and 90 min. At 2, 6 and 24 h after anaesthesia the maximum nausea will be rated for the 30‐120 min, 2‐6 h, and 6‐24 h interval; 3. Reduction of VRS nausea immediately at 2, 5, 7.5, 10, 15, 20 and 30 min after rescue treatment administration. Thereafter maximum nausea will be rated at 2, 6 and 24 hours after treatment for the 30‐120 min, 2‐6 h and 6‐24 h interval; Secondary Objective: Heart rate and blood pressure; Observer´s assessment of alertness and sedation scales; sensitifity and specificity characteristics for both the BIS and the cAAI; awareness after anaesthesia assessed by the Brice questionnaire at 2 and 24 hours after anaesthesia; occurrence of postoperative vomiting and the respective time‐points; usage of rescue medication, time and dosage; time to discharge from post anaesthetic care unit INCLUSION CRITERIA: Patients = 18 < 75 years; ASA physical status I‐II; Planned duration of anaesthesia > 60 min; Apfel score = 2‐3; elective (laparoscopic) surgery (abdominal, gynaecological) Are the trial subjects under 18? no Number of subjects for this age range: F.1.2 Adults (18‐64 years) yes F.1.2.1 Number of subjects for this age range F.1.3 Elderly (>=65 years) no F.1.3.1 Number of subjects for this age range