Please select the eligibility criteria that correspond to the clinical trial below.
Title: Evaluation of Nitrous Oxide In the Gas Mixture for Anaesthesia: a Randomised Controlled Trial
Brief Summary: We aim to investigate the effectiveness and safety of nitrous oxide (N2O) in anaesthesia.

Hypothesis In patients undergoing anaesthesia for major surgery, avoidance of N2O will reduce hospital length of stay when compared with otherwise identically managed surgical patients receiving N2O as a component of their anaesthesia.


Options:
A: Inclusion Criteria:

* mentally competent patients undergoing cesarean section under spinal or epidural anesthesia

Exclusion Criteria:

* fever/chorioamnionitis; GBS positive on antibiotics; immunocompromised / HIV patients; on antibiotics for any reason; general anesthesia; age less than 18 years custody patients stat cesarean section
B: Inclusion Criteria:

1. Males and females, age 18 years and over
2. Planned general anaesthesia for surgery that includes a skin incision and expected to exceed two hours, and the patient is expected to be in hospital for at least three days

Exclusion Criteria:

1. Endoscopic or radiological procedures
2. Cardiac surgery
3. Marked impairment of gas-exchange (requiring Fi02\> 0.3)
4. Thoracic surgery requiring one-lung ventilation (requiring Fi02\> 0.3)
5. Specific circumstances where N2O is contraindicated (eg. volvulus, pulmonary hypertension, raised intracranial pressure)
6. Lack of provision of N2O.
C: Inclusion Criteria:

* Age 18 years or older.
* Laparotomy, acute or elective. In case of gynaecological surgery only if malignancy is suspected (defined as risk of ovarian malignancy index \>200 or a specimen with atypical or neoplastic cells).

Exclusion Criteria:

* Other surgery within 30 days (except surgery in local anaesthesia).
* Chemotherapy within 3 months.
* Inability to give informed consent.
* Inability to keep oxygen saturation above 90% without supplemental oxygen (measured preoperatively by pulse oximetry).
D: Inclusion Criteria

1. Adult males and females age ≥ 45 years, undergoing noncardiac surgery and general anaesthesia expected to exceed two hours.
2. At increased risk of cardiac events, defined as any of

   1. history of coronary artery disease as defined by a history of any one of the following: i. angina ii. MI iii. segmental wall motion abnormality on echocardiography or a fixed defect on radionuclide imaging iv. a positive exercise stress test for cardiac ischaemia v. a positive radionuclide exercise, echocardiographic exercise, or pharmacological cardiovascular stress test for cardiac ischaemia vi. coronary revascularization (CABG or PTCA) vii. angiographic evidence of atherosclerotic stenosis \> 50% of the diameter of any coronary artery viii. ECG with pathological Q waves in two contiguous leads
   2. heart failure
   3. cerebrovascular disease thought due to atherothrombotic disease
   4. aortic or peripheral vascular disease
   5. or three or more of the following risk factors:

      * age ≥70 years
      * any history of congestive heart failure
      * diabetes and currently on an oral hypoglycaemic agent or insulin therapy
      * current treatment for hypertension
      * preoperative serum creatinine \>175 micro mol/L (\> 2.0 mg/dl)
      * current or previous high cholesterol ≥6.2 mmol/L (\> 240 mg/dl)
      * history of a transient ischemic attack (TIA) (i.e. a transient focal neurological deficit that lasted less than 24 hours and thought to be vascular in origin)
      * emergency/urgent surgery (i.e. surgery which must be undertaken within 24 hours of acute presentation to hospital)
      * high-risk type of surgery (i.e. intrathoracic or intraperitoneal)

Exclusion Criteria

1. having cardiac surgery
2. marked impairment of gas-exchange expected to require Fi02\> 0.5 intraoperatively
3. specific circumstances where N2O is contraindicated (eg. volvulus, pulmonary hypertension, raised intracranial pressure) or the anaesthetist plans to use supplemental oxygen (eg. colorectal surgery)
4. N2O unavailable for use.

Answer: B