Inclusion Criteria:
1. Onset of symptoms related to HAPE (including dyspnea at rest, cough, or exercise intolerance) within 7 days of ascending to high altitude (≥2500m).
2. Diagnosis of HAPE: requiring at least two symptoms (dyspnea at rest, cough, weakness/ decreased exercise performance, or chest tightness/congestion) and two clinical signs (rales or wheezing in at least one lung field, central cyanosis, tachypnea, or tachycardia) according to the STAR data reporting guidelines; plus imaging evidence of pulmonary edema.
3. Aged from 0 to 14 years old, without gender restriction.
4. Written informed consent obtained from the subject's legal guardian(s).
5. Refusal or inability to undergo immediate descent at the time of presentation.
Exclusion Criteria:
1. Severe respiratory failure requiring immediate endotracheal intubation upon hospital admission, including severe hypoxemia, acidosis and/or respiratory distress, upper-airway obstruction, inability to manage airway secretions, recurrent apnea, altered mental status, etc.
2. Pre-term infants with corrected gestational age ≤36 weeks.
3. Receipt of non-conventional respiratory support (e.g., HFNC, CPAP) for more than 2 hours within 24 hours prior to randomization, or planned use of other non-invasive respiratory support modalities.
4. Emergent conditions requiring invasive/surgical intervention, including untreated pneumothorax / pneumomediastinum, massive pleural effusion, high-altitude cerebral edema.
5. Pulmonary edema or hypoxemia attributable to other underlying diseases, such as congenital heart disease, chronic obstructive pulmonary disease, asthma, bronchopulmonary dysplasia, pulmonary infection, and others.
6. Status post tracheostomy.
7. Conditions precluding tolerance to HFNC, including unrepaired cleft palate, severe nasal malformation, recent craniofacial / nasal surgery.
8. Chronic home non-invasive ventilation use.
9. Pre-hospital hyperbaric oxygen chamber treatment prior to enrollment.
10. Presence of any serious medical conditions or clinically significant laboratory abnormalities that, in the investigator's judgment, may compromise subject safety or ability to complete the study.
11. Patients with signed Do Not Intubate (DNI) order or other limitations on the intensity of critical care treatment.
12. Participation in another drug or medical device clinical trial within 3 months, or prior enrollment in other interventional studies of the same category.
13. Refusal to sign the informed consent form.
