High frequency oscillatory ventilation (HFOV), as an ideal lung protection ventilation method, has been gradually applied to neonatal intensive care treatment, and is currently recommended as a rescue method for neonatal acute respiratory distress syndrome (ARDS) after failure of conventional mechanical ventilation. Although its ability to improve oxygenation and enhance carbon dioxide (CO2) clearance has been repeatedly demonstrated in laboratory studies, its impact on the clinical results of these patients is still uncertain. Noninvasive high-frequency oscillatory ventilation (nHFOV) combines the advantages of HFOV and non-invasive ventilation, and has become the current research focus in this field. It is recommended to use it after the failure of routine non-invasive ventilation treatment to avoid intubation. For the treatment of intubation, there is still a lack of large-scale clinical trials to systematically explore its efficacy. The gradual increase of clinical application of nHFOV has also enriched its application in the treatment of other diseases. At present, non-invasive high-frequency oscillatory ventilation has not been applied to the study of adult COVID-19 with acute hypoxemia, which will be the first study in this field.

Inclusion Criteria:

1. After COVID-19 nucleic acid detection, imaging confirmed COVID-19;
2. Age ≥ 18 years old;
3. At the time of admission, the blood gas was acute hypoxic respiratory failure, the fraction of inhaled oxygen concentration (Fio2) was at least 0.40, but the blood oxygen saturation (Spo2) was 94% or lower;
4. Be able to follow the instructions of the researcher.

Exclusion Criteria:

1. Critically ill patients: cardiac and respiratory arrest, requiring tracheal intubation; Multiple organ failure (>2 organs);
2. Hemodynamic instability;
3. After extubation of invasive mechanical ventilation;
4. Patients who cannot wear a mask, such as maxillofacial or upper airway surgery;
5. Patients who may affect the treatment effect of NPPV, such as nasal obstruction or upper respiratory tract obstruction;
6. Obvious bullae, pneumothorax and pleural effusion;
7. It is accompanied by obvious other respiratory diseases, such as bronchiectasis and lung cancer;
8. Those who refuse to participate in this test.