Preliminary studies have shown that NPPV can avoid tracheal intubation in 40% to 60% patients who have severe exacerbation of COPD. Recently, large-scale comparative effectiveness research (CER) also found that compared with invasive ventilation, NPPV can reduce mortality rates. But there's no high-quality clinical studies which can confirm this. Therefore, investigators believe that NPPV can avoid intubation in patients with severe exacerbation of COPD in ICU with perfect monitoring conditions and reasonable human resource allocation, in order to reduce IMV-related complications and improve patients' outcomes.

In part of the patients who were AECOPD with pH <7.25 , preliminary studies have shown that NPPV can avoid tracheal intubation in 40% to 60% patients, and also reduce the incidence of VAP. Recently, large-scale comparative effectiveness research (CER) also found that compared with invasive ventilation, NPPV can reduce mortality rates. At present, there's no high-quality clinical studies which can confirm this, and clinical guidelines do not have a recommendation on the use of NPPV in these patients. Therefore, investigators believe that NPPV can avoid intubation in patients with severe exacerbation of COPD in ICU with perfect monitoring conditions and reasonable human resource allocation, as well as the progress of medical technology in NPPV in recent years, in order to reduce IMV-related complications and improve patients' outcomes.

Inclusion Criteria:

• AECOPD;

Exclusion Criteria:

• refuse to engage in the study;
• have been included in other study.

All patients with acute exacerbation of chronic obstructive pulmonary disease in medical ICU.