The goal of this clinical trial is to investigate the efficacy of high-flow nasal cannula oxygen therapy (HFNC) combined with sequential non-invasive ventilation (NIV) in patients with chronic obstructive pulmonary disease complicated with type II respiratory failure. The main questions it aims to answer are:

What is the effect of high-flow nasal cannula oxygen therapy (HFNC) combined with sequential non-invasive ventilation on arterial blood gas indicators in patients with chronic obstructive pulmonary disease and type II respiratory failure? What is the effect of high-flow nasal cannula oxygen therapy (HFNC) combined with sequential non-invasive ventilation on pulmonary ventilation function in patients with chronic obstructive pulmonary disease and type II respiratory failure? What is the effect of high-flow nasal cannula oxygen therapy (HFNC) combined with sequential non-invasive ventilation on vital signs in patients with chronic obstructive pulmonary disease and type II respiratory failure? What is the effect of high-flow nasal cannula oxygen therapy (HFNC) combined with sequential non-invasive ventilation on the quality of life of patients with chronic obstructive pulmonary disease and type II respiratory failure? What is the effect of high-flow nasal cannula oxygen therapy (HFNC) combined with sequential non-invasive ventilation on complications in patients with chronic obstructive pulmonary disease and type II respiratory failure?

Participants will:

Receive NIV through a full mask or nasal mask using any of the existing ventilators in the hospital Receive other standard treatments according to the latest GOLD guidelines The general data of patients, arterial blood gas index, pulmonary ventilation function, vital signs index, quality of life and complications before and after treatment were collected.

Inclusion Criteria:

• All subjects included in the study met the diagnostic criteria for AECOPD in the Global Initiative for Chronic Obstructive Pulmonary Disease (2014 Update);
• Age > 18 years old;
• All patients met the diagnostic criteria for type II respiratory failure in the eighth edition of ' Internal Medicine ', that was, arterial blood PaO2 < 50mmHg;
• The patient was conscious, without myocardial infarction, acute stroke, severe liver and kidney dysfunction, severe coagulation dysfunction and other diseases;
• The patient did not have life-threatening hypoxemia and severe hemodynamic instability, and did not need tracheal intubation or tracheotomy;
• Patients can cooperate with pulmonary function tests.

Exclusion Criteria:

• Patients with pneumothorax, mediastinal emphysema or severe thoracic deformity;
• Patients with bronchial asthma, interstitial pneumonia and other diseases;
• Patients with coma and disturbance of consciousness;
• The upper respiratory tract or facial injury and facial deformity, can not wear a good nose (face) mask;
• Patients with septic shock or severe heart, kidney, liver and other diseases;
• Sputum and sticky, unable to expectoration or prone to aspiration caused by airway obstruction.
• Automatic discharge or transfer, or due to non-respiratory serious diseases (including non-invasive ventilator complications, non-invasive ventilation treatment ineffective need to be changed to invasive ventilation), termination of the study patients.