Please assess the completion status of the following clinical trial:

Trial Title: International Substudy Enigma2 on Postoperative Cognitive Disorders

Study Design Characteristics:
- Allocation: RANDOMIZED
- Intervention Model: PARALLEL
- Observational Model: None
- Primary Purpose: TREATMENT
- Time Perspective: None
- Masking: TRIPLE
- Phase: PHASE4
- Number of Arms: 2.0

Eligibility Criteria:
Inclusion Criteria:~Adult males and females aged ≥ 45 years, undergoing noncardiac surgery and general anaesthesia that exceeds two hours.~At increased risk of cardiac events, defined as any of:~* history of coronary artery disease (angina, MI, Coronary revascularisation-Coronary Artery Bypass Graft (CABG) and Percutaneous Transluminal Coronary Angiography ( PTCA)-, positive stress testing, angiography/other imaging, Q waves on ECG)~* heart failure~* cerebrovascular disease due to atherothrombotic disease~* aortic or peripheral vascular disease~OR~three or more of the following risk factors: age ≥70 years, history of heart failure, diabetes (medicated), hypertension (medicated), preoperative serum creatinine \>175 mmol/L, cholesterol ≥6.2 mmol/L, history of a transient ischemic attack (TIA),~Exclusion Criteria:~1. Dementia (MMS test≤24)~2. Parkinson Disease~3. Patients taking regularly (\>2 weeks) tricyclic antidepressants or neuroleptics~4. Patients suffering from Alcohol Dependency (WHO CRITERIA )~5. Patients suffering from severe hypoacusis or visual loss or any other reason hindering the CANTAB battery testing process~6. Patients with untreated deficit in Vitamin B6, B12 and folic acid~7. Patients with marked impairment of gas-exchange requiring Fi02\> 0.5 intraoperatively~8. Patients with specific circumstances where N2O is contraindicated (eg. volvulus, pulmonary hypertension, raised intracranial pressure) or the use of supplemental oxygen is planned (eg. colorectal surgery)~9. N2O unavailable

- Gender: ALL
- Minimum Age: 18 Years
- Maximum Age: None
- Healthy Volunteers: f

Study Arms:
- Nitrous Oxide (Type: ACTIVE_COMPARATOR): Receives a mixture of 70% Nitrous Oxide in 30% Oxygen
- Air/Oxygen (placebo) (Type: PLACEBO_COMPARATOR): Receives a mixture of 70% Air in 30% Oxygen

Based on this trial design, predict the completion outcome and termination type (if applicable).