Coronary Artery DiseasePhase 4NCT00430989
The ENIGMA II Trial:Nitrous Oxide Anaesthesia and Cardiac Morbidity After Major Surgery: a Randomised Controlled Trial
A Phase 4 study testing Nitrous Oxide and No Nitrous Oxide in people with Coronary Artery Disease, run by Bayside Health at 1 site in Australia.
Trial summary
To investigate the safety of nitrous oxide (N2O) anaesthesia in patients with risk factors for coronary artery disease undergoing major surgery. Read more about this study
- Who is it for?
- Ages 18 years and older
- Conditions the study is for
- Coronary Artery Disease
- What is being tested?
- Nitrous Oxide and No Nitrous Oxide
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 7,112 participants
- Where
- 1 siteAustralia
- Study dates
- Apr 2007to Sep 2013
- Phase
- Phase 4
- Are there results?
- Yes, posted in the registrySummary in the doctors' view
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- All sexes
- No healthy volunteers
- Adult, Older adult
Who may be able to join
- Adult males and females age ≥ 45 years, undergoing noncardiac surgery and general anaesthesia expected to exceed two hours.
- At increased risk of cardiac events, defined as any of
- 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
- heart failure
- cerebrovascular disease thought due to atherothrombotic disease
- aortic or peripheral vascular disease
Show all 16Show fewer
- 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)
Who cannot join
- having cardiac surgery
- marked impairment of gas-exchange expected to require Fi02> 0.5 intraoperatively
- specific circumstances where N2O is contraindicated (eg. volvulus, pulmonary hypertension, raised intracranial pressure) or the anaesthetist plans to use supplemental oxygen (eg. colorectal surgery)
- N2O unavailable for use.
Trial locations and contacts
1 site in 1 country.
About this study
Official title: Large, Randomised, Parallel-group, Controlled Trial, With Patients Randomly Allocated to Either N2O-containing (70% N2O in Oxygen [FiO2 0.3]) or N2O-free (70% Nitrogen in Oxygen [FiO2 0.3]).
To investigate the safety of nitrous oxide (N2O) anaesthesia in patients with risk factors for coronary artery disease undergoing major surgery.
Read the detailed description
Approximately 25% of patients undergoing major surgery have known coronary artery disease (CAD) or risk factors for CAD.
N2O interferes with vitamin B12 and folate metabolism. This impairs production of methionine (from homocysteine), used to form tetrahydrofolate and thymidine during DNA synthesis. It has been repeatedly demonstrated that N2O anaesthesia increases postoperative homocysteine levels. Chronic hyperhomocysteinaemia is associated with cardiovascular disease, and acute hyperhomocysteinaemia is known to cause endothelial dysfunction. One small trial has demonstrated an increased incidence of postoperative myocardial ischaemia in patients receiving N2O anaesthesia. Reducing postoperative myocardial infarction and death are important aims for those with CAD undergoing major surgery.
Our previous trial (ENIGMA) studied 2050 patients and identified some serious adverse effects, but most patients were not at risk of CAD and so we could not reliably assess serious cardiac complications. We propose a large simple randomized clinical trial of 7,000 patients to provide a definitive evaluation of the safety of N2O anaesthesia.
Updated statistical analysis plan can be found at www.enigma2.org.au.
- Conditions
- Coronary Artery Disease
- Being tested
- Nitrous Oxide, No Nitrous Oxide
- Keywords
- Anaesthesia, Major Surgery, Coronary artery disease, Nitrous oxide, Effects of Nitrous Oxide following Anaesthesia, Anaesthesia and coronary artery disease
- Medical subject headings
- Coronary Artery Disease
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Nitrous OxideOther
General anaesthesia with the inclusion of Nitrous Oxide at 70%
No Nitrous OxideOther
General anaesthesia with no use of Nitrous Oxide
| Study group | Role | What they receive |
|---|---|---|
| 70% Nitrous Oxide | Other | General anaesthesia using 70% Nitrous Oxide with fraction of inspired oxygen at 30% Receives: Other: Nitrous Oxide |
| No Nitrous Oxide | Other | General anaesthesia not containing Nitrous oxide with fraction of inspired oxygen at 30% Receives: Other: No Nitrous Oxide |
What is being measured
The primary outcome is the main question the study is designed to answer.
The Primary Endpoint is a Composite of Death and Cardiovascular Events (Clinical and Silent MI, Cardiac Failure, Cardiac Arrest, Pulmonary Embolism, and Stroke) Measured at 30 Days After Surgery.
Measured: 30 days post op
Secondary outcomes (6)
Myocardial Infarction (MI)
Measured: 30 days post op
Cardiac Arrest
Measured: 30 days
Pulmonary Embolism
Measured: 30 Days Post op
Stroke
Measured: 30 Days Post op
Wound Infection
Measured: 30 Days Post op
Hospital Stay (Days)
Measured: 30 Days Post Op
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted2 Feb 2007 (estimated)
- Study startApr 2007
- Primary completionSep 2013
- Study completionSep 2013
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Posted resultsParticipant flow, outcome measures and adverse events reported by the sponsor.
- Publications (6)Papers the sponsor has linked to this study.
- Other trials for Coronary Artery DiseaseStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 4
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- international, randomised, assessor-blinded trial in patients aged at least 45 years with known or suspected coronary artery disease having major non-cardiac surgery.
- Masking
- Triple blind
- Who is masked
- Participant, Care provider, Outcomes assessor
- Enrolment
- 7,112 participants (actual)
Sponsor and investigators
- Lead sponsor
- Bayside Health
- Sponsor type
- Other government
- Collaborators
- National Health and Medical Research Council, Australia
- Responsible party
- Sponsor
- Investigators
- Paul S Myles, MBBS MPH MD, Principal investigator, The Alfred
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT00430989
- Sponsor's protocol ID
- 6/07
- Status last verified
- Dec 2025
- First submitted
- 31 Jan 2007
- Last updated
- 20 Jan 2026
- Results posted
- Yes, on ClinicalTrials.gov
- Data monitoring committee
- Yes
- Individual data sharing
- No
Publications
Asghari-Jafarabadi M, Myles PS, Coulson TG, Winter N, Corcoran TB, Chan MTV, Wu WKK, Peyton P, Leslie K, Forbes A. Integrating machine learning and pathway modelling to explore factors associated with chronic post-surgical pain and quality of life: a secondary observational analysis of the ENIGMA-II trial. BJA Open. 2026 Jun 17;19:100570. doi: 10.1016/j.bjao.2026.100570. eCollection 2026 Sep.
PubMed 42376225Beattie WS, Wijeysundera DN, Chan MTV, Peyton PJ, Leslie K, Paech MJ, Sessler DI, Wallace S, Myles PS, Galagher W, Farrington C, Ditoro A, Baulch S, Sidiropoulos S, Bulach R, Bryant D, O'Loughlin E, Mitteregger V, Bolsin S, Osborne C, McRae R, Backstrom M, Cotter R, March S, Silbert B, Said S, Halliwell R, Cope J, Fahlbusch D, Crump D, Thompson G, Jefferies A, Reeves M, Buckley N, Tidy T, Schricker T, Lattermann R, Iannuzzi D, Carroll J, Jacka M, Bryden C, Badner N, Tsang MWY, Cheng BCP, Fong ACM, Chu LCY, Koo EGY, Mohd N, Ming LE, Campbell D, McAllister D, Walker S, Olliff S, Kennedy R, Eldawlatly A, Alzahrani T, Chua N, Sneyd R, McMillan H, Parkinson I, Brennan A, Balaji P, Nightingale J, Kunst G, Dickinson M, Subramaniam B, Banner-Godspeed V, Liu J, Kurz A, Hesler B, Fu AY, Egan C, Fiffick AN, Hutcherson MT, Turan A, Naylor A, Obal D, Cooke E; ANZCA Clinical Trials Network for the ENIGMA-II Investigators. Implication of Major Adverse Postoperative Events and Myocardial Injury on Disability and Survival: A Planned Subanalysis of the ENIGMA-II Trial. Anesth Analg. 2018 Nov;127(5):1118-1126. doi: 10.1213/ANE.0000000000003310.
PubMed 29533264Corcoran T, Kasza J, Short TG, O'Loughlin E, Chan MT, Leslie K, Forbes A, Paech M, Myles P; ENIGMA-II investigators. Intraoperative dexamethasone does not increase the risk of postoperative wound infection: a propensity score-matched post hoc analysis of the ENIGMA-II trial (EnDEX). Br J Anaesth. 2017 Feb;118(2):190-199. doi: 10.1093/bja/aew446.
PubMed 28100522Chan MT, Peyton PJ, Myles PS, Leslie K, Buckley N, Kasza J, Paech MJ, Beattie WS, Sessler DI, Forbes A, Wallace S, Chen Y, Tian Y, Wu WK; and the Australian and New Zealand College of Anaesthetists Clinical Trials Network for the ENIGMA-II investigators. Chronic postsurgical pain in the Evaluation of Nitrous Oxide in the Gas Mixture for Anaesthesia (ENIGMA)-II trial. Br J Anaesth. 2016 Dec;117(6):801-811. doi: 10.1093/bja/aew338.
PubMed 27956679Myles PS, Leslie K, Chan MT, Forbes A, Peyton PJ, Paech MJ, Beattie WS, Sessler DI, Devereaux PJ, Silbert B, Schricker T, Wallace S; ANZCA Trials Group for the ENIGMA-II investigators. The safety of addition of nitrous oxide to general anaesthesia in at-risk patients having major non-cardiac surgery (ENIGMA-II): a randomised, single-blind trial. Lancet. 2014 Oct 18;384(9952):1446-54. doi: 10.1016/S0140-6736(14)60893-X.
PubMed 25142708Myles PS, Leslie K, Peyton P, Paech M, Forbes A, Chan MT, Sessler D, Devereaux PJ, Silbert BS, Jamrozik K, Beattie S, Badner N, Tomlinson J, Wallace S; ANZCA Trials Group. Nitrous oxide and perioperative cardiac morbidity (ENIGMA-II) Trial: rationale and design. Am Heart J. 2009 Mar;157(3):488-494.e1. doi: 10.1016/j.ahj.2008.11.015.
PubMed 19249419
Study at a glance
From the registry record, last updated by the sponsor on 20 Jan 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Large, Randomised, Parallel-group, Controlled Trial, With Patients Randomly Allocated to Either N2O-containing (70% N2O in Oxygen [FiO2 0.3]) or N2O-free (70% Nitrogen in Oxygen [FiO2 0.3]).
- ClinicalTrials.gov ID
- NCT00430989
- Acronym / sponsor ID
- 6/07
- Conditions
- Coronary Artery Disease
- Keywords
- Anaesthesia, Major Surgery, Coronary artery disease, Nitrous oxide, Effects of Nitrous Oxide following Anaesthesia, Anaesthesia and coronary artery disease
- Phase
- Phase 4
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 7,112 participants (actual)
- Lead sponsor
- Bayside HealthOther government
- Collaborators
- National Health and Medical Research Council, Australia
- Study start
- Apr 2007
- Primary completion
- Sep 2013 (actual)
- Study completion
- Sep 2013 (actual)
- First posted
- 2 Feb 2007 (estimated)
- Results
- Posted 17 Jun 2019
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
To investigate the safety of nitrous oxide (N2O) anaesthesia in patients with risk factors for coronary artery disease undergoing major surgery.
Detailed description
Approximately 25% of patients undergoing major surgery have known coronary artery disease (CAD) or risk factors for CAD.
N2O interferes with vitamin B12 and folate metabolism. This impairs production of methionine (from homocysteine), used to form tetrahydrofolate and thymidine during DNA synthesis. It has been repeatedly demonstrated that N2O anaesthesia increases postoperative homocysteine levels. Chronic hyperhomocysteinaemia is associated with cardiovascular disease, and acute hyperhomocysteinaemia is known to cause endothelial dysfunction. One small trial has demonstrated an increased incidence of postoperative myocardial ischaemia in patients receiving N2O anaesthesia. Reducing postoperative myocardial infarction and death are important aims for those with CAD undergoing major surgery.
Our previous trial (ENIGMA) studied 2050 patients and identified some serious adverse effects, but most patients were not at risk of CAD and so we could not reliably assess serious cardiac complications. We propose a large simple randomized clinical trial of 7,000 patients to provide a definitive evaluation of the safety of N2O anaesthesia.
Updated statistical analysis plan can be found at www.enigma2.org.au.
Study design
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Triple blind (participant, care provider, outcomes assessor)
- Number of arms
- 2
- Model description
- international, randomised, assessor-blinded trial in patients aged at least 45 years with known or suspected coronary artery disease having major non-cardiac surgery.
| Arm | Type | Receives |
|---|---|---|
| 70% Nitrous Oxide | Other | Other: Nitrous OxideGeneral anaesthesia using 70% Nitrous Oxide with fraction of inspired oxygen at 30% |
| No Nitrous Oxide | Other | Other: No Nitrous OxideGeneral anaesthesia not containing Nitrous oxide with fraction of inspired oxygen at 30% |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (16 listed)
- Adult males and females age ≥ 45 years, undergoing noncardiac surgery and general anaesthesia expected to exceed two hours.
- At increased risk of cardiac events, defined as any of
Key exclusion criteria (4 listed)
- having cardiac surgery
- marked impairment of gas-exchange expected to require Fi02> 0.5 intraoperatively
- specific circumstances where N2O is contraindicated (eg. volvulus, pulmonary hypertension, raised intracranial pressure) or the anaesthetist plans to use supplemental oxygen (eg. colorectal surgery)
- N2O unavailable for use.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Nitrous OxideGeneral anaesthesia with the inclusion of Nitrous Oxide at 70% | Other | 70% Nitrous Oxide |
| No Nitrous OxideGeneral anaesthesia with no use of Nitrous Oxide | Other | No Nitrous Oxide |
Primary outcome
The Primary Endpoint is a Composite of Death and Cardiovascular Events (Clinical and Silent MI, Cardiac Failure, Cardiac Arrest, Pulmonary Embolism, and Stroke) Measured at 30 Days After Surgery.
Time frame: 30 days post op
6 secondary outcomes
Myocardial Infarction (MI)
Time frame: 30 days post op
Cardiac Arrest
Time frame: 30 days
Pulmonary Embolism
Time frame: 30 Days Post op
Stroke
Time frame: 30 Days Post op
Wound Infection
Time frame: 30 Days Post op
Hospital Stay (Days)
Time frame: 30 Days Post Op
Results and safety
Loading the posted results from ClinicalTrials.gov…
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 20 Jan 2026.
- Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
- Derived from this study: PubMed 42376225Asghari-Jafarabadi M, Myles PS, Coulson TG, Winter N, Corcoran TB, Chan MTV, Wu WKK, Peyton P, Leslie K, Forbes A. Integrating machine learning and pathway modelling to explore factors associated with chronic post-surgical pain and quality of life: a secondary observational analysis of the ENIGMA-II trial. BJA Open. 2026 Jun 17;19:100570. doi: 10.1016/j.bjao.2026.100570. eCollection 2026 Sep.
- Derived from this study: PubMed 29533264Beattie WS, Wijeysundera DN, Chan MTV, Peyton PJ, Leslie K, Paech MJ, Sessler DI, Wallace S, Myles PS, Galagher W, Farrington C, Ditoro A, Baulch S, Sidiropoulos S, Bulach R, Bryant D, O'Loughlin E, Mitteregger V, Bolsin S, Osborne C, McRae R, Backstrom M, Cotter R, March S, Silbert B, Said S, Halliwell R, Cope J, Fahlbusch D, Crump D, Thompson G, Jefferies A, Reeves M, Buckley N, Tidy T, Schricker T, Lattermann R, Iannuzzi D, Carroll J, Jacka M, Bryden C, Badner N, Tsang MWY, Cheng BCP, Fong ACM, Chu LCY, Koo EGY, Mohd N, Ming LE, Campbell D, McAllister D, Walker S, Olliff S, Kennedy R, Eldawlatly A, Alzahrani T, Chua N, Sneyd R, McMillan H, Parkinson I, Brennan A, Balaji P, Nightingale J, Kunst G, Dickinson M, Subramaniam B, Banner-Godspeed V, Liu J, Kurz A, Hesler B, Fu AY, Egan C, Fiffick AN, Hutcherson MT, Turan A, Naylor A, Obal D, Cooke E; ANZCA Clinical Trials Network for the ENIGMA-II Investigators. Implication of Major Adverse Postoperative Events and Myocardial Injury on Disability and Survival: A Planned Subanalysis of the ENIGMA-II Trial. Anesth Analg. 2018 Nov;127(5):1118-1126. doi: 10.1213/ANE.0000000000003310.
- Derived from this study: PubMed 28100522Corcoran T, Kasza J, Short TG, O'Loughlin E, Chan MT, Leslie K, Forbes A, Paech M, Myles P; ENIGMA-II investigators. Intraoperative dexamethasone does not increase the risk of postoperative wound infection: a propensity score-matched post hoc analysis of the ENIGMA-II trial (EnDEX). Br J Anaesth. 2017 Feb;118(2):190-199. doi: 10.1093/bja/aew446.
- Derived from this study: PubMed 27956679Chan MT, Peyton PJ, Myles PS, Leslie K, Buckley N, Kasza J, Paech MJ, Beattie WS, Sessler DI, Forbes A, Wallace S, Chen Y, Tian Y, Wu WK; and the Australian and New Zealand College of Anaesthetists Clinical Trials Network for the ENIGMA-II investigators. Chronic postsurgical pain in the Evaluation of Nitrous Oxide in the Gas Mixture for Anaesthesia (ENIGMA)-II trial. Br J Anaesth. 2016 Dec;117(6):801-811. doi: 10.1093/bja/aew338.
- Derived from this study: PubMed 25142708Myles PS, Leslie K, Chan MT, Forbes A, Peyton PJ, Paech MJ, Beattie WS, Sessler DI, Devereaux PJ, Silbert B, Schricker T, Wallace S; ANZCA Trials Group for the ENIGMA-II investigators. The safety of addition of nitrous oxide to general anaesthesia in at-risk patients having major non-cardiac surgery (ENIGMA-II): a randomised, single-blind trial. Lancet. 2014 Oct 18;384(9952):1446-54. doi: 10.1016/S0140-6736(14)60893-X.
- Derived from this study: PubMed 19249419Myles PS, Leslie K, Peyton P, Paech M, Forbes A, Chan MT, Sessler D, Devereaux PJ, Silbert BS, Jamrozik K, Beattie S, Badner N, Tomlinson J, Wallace S; ANZCA Trials Group. Nitrous oxide and perioperative cardiac morbidity (ENIGMA-II) Trial: rationale and design. Am Heart J. 2009 Mar;157(3):488-494.e1. doi: 10.1016/j.ahj.2008.11.015.
- Individual participant dataSharing planned: No
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Paul S Myles, MBBS MPH MD principal investigator
The Alfred
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 4 study testing Nitrous Oxide and No Nitrous Oxide in people with Coronary Artery Disease, run by Bayside Health at 1 site in Australia.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 16 inclusion and 4 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 20 Jan 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Australia. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this phase mean?
Phase 4 studies take place after a treatment is approved, to learn more about its long-term benefits and risks in everyday use.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
Yes. Results are posted in the registry (first posted 17 Jun 2019). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
The Primary Endpoint is a Composite of Death and Cardiovascular Events (Clinical and Silent MI, Cardiac Failure, Cardiac Arrest, Pulmonary Embolism, and Stroke) Measured at 30 Days After Surgery. (time frame: 30 days post op). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT00430989, which also lists 6 linked publications.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 20 Jan 2026.