Please assess the completion status of the following clinical trial:

Trial Title: Continuous Positive Airway Pressure and Acetazolamide to Treat Sleep Apnea Syndrome Patients at Altitude

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

Eligibility Criteria:
Inclusion Criteria:~* Obstructive sleep apnea syndrome, successfully on CPAP therapy~* Residence at low altitude (\< 800 m)~* Obstructive apnea/hypopnea index \>20/h and a complaint of excessive daytime sleepiness before introduction of CPAP therapy~* \> 15 oxygen desaturations/h (\> 3% dips) during an ambulatory nocturnal pulse oximetry performed at the end of a 4-night period without CPAP~Exclusion Criteria:~* Sleep disorders other than OSA~* More than mild cardiovascular disease, unstable cardiovascular disease~* Any lung disease, pulmonary hypertension~* Chronic rhinitis~* Treatment with drugs that affect respiratory center drive (benzodiazepines or other sedatives or sleep inducing drugs, morphine or codeine derivates), stimulants (modafinil, methylphenidate, theophylline)~* Internal, neurologic or psychiatric disease that interfere with sleep quality~* Previous intolerance to moderate or low altitude (\< 2600 m)~* Exposure to altitudes \> 1500m for \> 1 day within the last 4 weeks before the study

- Gender: ALL
- Minimum Age: 20 Years
- Maximum Age: 80 Years
- Healthy Volunteers: f

Study Arms:
- acetazolamide (Type: EXPERIMENTAL): combination of acetazolamide and nocturnal continuous positive airway pressure ventilation
- placebo capsules (Type: PLACEBO_COMPARATOR): combination of placebo and nocturnal continuous positive airway pressure ventilation

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