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ENIGMA - Evaluation of Nitrous Oxide In the Gas Mixture for Anaesthesia: a Randomised Controlled Trial

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details. Identifier: NCT00164047
Recruitment Status : Completed
First Posted : September 14, 2005
Last Update Posted : July 31, 2009
National Health and Medical Research Council, Australia
Australia: Theapeutic Goods Administration
Information provided by:
Bayside Health

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.

Condition or disease Intervention/treatment Phase
Quality of Recovery From Anaesthesia Effects of Nitrous Oxide Following Anaesthesia Induced Endothelial Dysfunction Drug: Nitrous Oxide Phase 4

Detailed Description:

There are some compelling reasons to question the routine use of nitrous oxide (N2O), also known as "laughing gas". Despite being the first anaesthetic drug introduced, and still widely used, there is sufficient doubt as to the risk-benefit profile.

There is strong evidence that N2O is a major risk factor for postoperative nausea and vomiting. It is clear that (even) brief exposure to N2O impairs methionine synthetase, an enzyme required for DNA production, red and white blood cell formation. Tissue hypoxia may be more common. These adverse effects are enhanced in "sick" patients (ie. those at highest risk, increased hospital length of stay and healthcare expenditure), and will be more likely in longer surgery. The extent of wound infection and cardiac morbidity associated with N2O is not known.

Large outcome trial data are lacking. When considering its widespread use in about 90% of all surgery around the world, small differences in outcome would have major implications for healthcare delivery. A large randomised controlled trial is necessary to answer this question.

We have recruited 2000 patients from about 25 centres around the world (mostly Australasia), who are undergoing major surgery.

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Study Type : Interventional  (Clinical Trial)
Estimated Enrollment : 2070 participants
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Single
Primary Purpose: Prevention
Official Title: Evaluation of Nitrous Oxide In the Gas Mixture for Anaesthesia: a Randomised Controlled Trial
Study Start Date : April 2003
Actual Primary Completion Date : December 2004
Actual Study Completion Date : December 2004

Resource links provided by the National Library of Medicine

Primary Outcome Measures :
  1. The primary endpoint is hospital length of stay (LOS), defined from the start of surgery until actual hospital discharge. Patients transferred to another hospital will be tracked until final discharge to home (or other final destination). LOS is likely

Secondary Outcome Measures :
  1. Secondary endpoints will be detected by a research assistant who will be masked to Group identity, using chart review up to 30 days postoperatively; confirmation of each will be sought by an independent member of the Endpoint Committee:
  2. Wound infection - if associated with purulent discharge or a positive microbial culture (46)
  3. Myocardial infarction - confirmed by ECG and/or troponin or CK-MB enzyme rise
  4. Venous thromboembolism - symptomatic DVT or PE, confirmed by venography, duplex ultrasonography, V-Q scan or spiral CT, or autopsy
  5. Stroke - a new neurological deficit persisting for 24 hours, confirmed by neurologist assessment and/or CT scan or MRI
  6. Awareness - postoperative recollection of intraoperative events
  7. Blood transfusion - any red cell transfusion within 30 days of surgery
  8. Pneumothorax, atelectasis, or pneumonia - confirmed by chest x-ray; for pneumonia: also 2 or more of temp> 38oC, white cell count >12,000/ml, positive sputum culture
  9. Severe vomiting - at least 2 episodes >6 hrs apart, or if requiring >2 doses of antiemetic medication
  10. Quality of recovery on the morning after surgery -using the validated QoR Score instrument (14), a 9-item patient-orientated measure of early postoperative health status. This is associated with patient satisfaction.
  11. 30-day mortality - for safety analysis only (study not powered for this rare event).

Information from the National Library of Medicine

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Ages Eligible for Study:   18 Years and older   (Adult, Older Adult)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   No

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.

Information from the National Library of Medicine

To learn more about this study, you or your doctor may contact the study research staff using the contact information provided by the sponsor.

Please refer to this study by its identifier (NCT number): NCT00164047

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Australia, Victoria
Alfred Hospital
Melbourne, Victoria, Australia, 3004
Sponsors and Collaborators
Bayside Health
National Health and Medical Research Council, Australia
Australia: Theapeutic Goods Administration
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Principal Investigator: Paul S Myles, MB BS MPH MD The Alfred
Publications of Results:
Other Publications:
Publications automatically indexed to this study by Identifier (NCT Number):
Layout table for additonal information Identifier: NCT00164047    
Other Study ID Numbers: 204/02
NHMRC 236956
First Posted: September 14, 2005    Key Record Dates
Last Update Posted: July 31, 2009
Last Verified: July 2009
Keywords provided by Bayside Health:
Nitrous Oxide
Additional relevant MeSH terms:
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Nitrous Oxide
Anesthetics, Inhalation
Anesthetics, General
Central Nervous System Depressants
Physiological Effects of Drugs
Analgesics, Non-Narcotic
Sensory System Agents
Peripheral Nervous System Agents