Please assess the completion status of the following clinical trial:

Trial Title: Dexmedetomidine Supplemented Analgesia in Patients at High-risk of Obstructive Sleep Apnea

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

Eligibility Criteria:
Inclusion Criteria:~1. Age \>=18 years but \<=80 years;~2. At high-risk of obstructive sleep apnea (a STOP-Bang score ≥3 combined with a serum bicarbonate ≥28 mmol/ L), but does not regularly receive continuous positive airway pressure (CPAP) therapy;~3. Scheduled to undergo major noncardiac surgery under general anesthesia, with an expected duration of \>=1 hours and planned to use patient-controlled intravenous analgesia (PCIA) after surgery.~Exclusion Criteria:~1. Diagnosed as central sleep apnea syndrome;~2. Preoperative history of severe central nervous system diseases (epilepsy, parkinsonism, intracranial tumor, craniocerebral trauma) or neuromuscular disorders (myasthenia gravis);~3. History of schizophrenia or other mental disorders, or antidepressant or anxiolytic therapy within 3 month before surgery;~4. Inability to communicate in the preoperative period because of coma, profound dementia, deafness or language barriers;~5. History of drug or alcohol dependence, or sedative or hypnotic therapy within 1 month before surgery;~6. Contraindications to HFNC therapy (e.g. mediastinal emphysema, shock, cerebrospinal fluid leakage, nasosinusitis, otitis media, glaucoma);~7. Severe tracheal or pulmonary disease (e.g. bullous lung disease, pneumothorax, tracheal fistula);~8. Sick sinus syndrome, severe sinus bradycardia (\<50 beats per minute), or second-degree or above atrioventricular block without pacemaker；~9. Severe hepatic dysfunction (Child-Pugh class C); Severe renal dysfunction (requirement of renal replacement therapy); severe heart dysfunction (preoperative New York Heart Association functional classification ≥3 or left ventricular ejection fraction \<30%); ASA classification IV or above; or expected survival \<24 hours after surgery;~10. Preoperative use of CPAP or HFNC therapy;~11. Expected intensive care unit (ICU) admission with tracheal intubation after surgery;~12. Refuse to participate in this study;~13. Other conditions that are considered unsuitable for study participation.

- Gender: ALL
- Minimum Age: 18 Years
- Maximum Age: 80 Years
- Healthy Volunteers: f

Study Arms:
- Dexmedetomidine group (Type: EXPERIMENTAL): Patient-controlled analgesia is established with morphine (0.5 mg/ml) and dexmedetomidine (1.25 microgram/ml) in a total volume of 160 ml. The pump is programmed to deliver 2-ml boluses at 6 to 8-minute lockout intervals with a background infusion rate at 1 ml/h. Patient-controlled analgesia is provided for at least 24 hours after surgery.
- Placebo group (Type: PLACEBO_COMPARATOR): Patient-controlled analgesia is established with morphine (0.5 mg/ml) in a total volume of 160 ml. The pump is programmed to deliver 2-ml boluses at 6 to 8-minute lockout intervals with a background infusion rate at 1 ml/h. Patient-controlled analgesia is provided for at least 24 hours after surgery.

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