The pathophysiological characteristics of respiratory failure on exacerbation of chronic pulmonary obstructive disease are the rapid deteriorate of respiratory symptoms, combined with aggravated flow limitation, gas trapping, dynamic pulmonary hyperinflation (DPH), therefore the intrinsic PEEP (PEEPi) increases. It is worthwhile to explore bedside methods to quantify the changes in dynamic pulmonary hyperinflation to guide safe and effective mechanical ventilation in airflow limited patients.

The study hypothesizes that the electrical impedence tomography (EIT) measured the changes of end expiratory lung impedence (△EELI） could accurately predict the changes of end expiratory lung volume （△EELV） measured by passive expiratory in controlled mechanical ventilated exacerbation COPD patients. The research intended to conduct a research to explore the relationship between △EELI and △EELV induced by external PEEP changes in ventilated exacerbation COPD patients.

Inclusion Criteria:

• 2022.7-2023.1 exacerbation COPD invasive ventilated patients admitted to the first affiliated Guangzhou medical university; 35 to 80 years old; in stable condition judged by clinicians

Exclusion Criteria:

• SpO2<88%; instable hemodynamic (MAP<65mmHg；Norepinephrine> 0.1ug/kg.min); pregnancy; 4 hour intravenous diuretics use before research; chest deformity and trauma, subpleural pulmonary bulla; implanted electronic devices(cardiac pacemaker, implantable cardioversion defibrillator,ect); tumour or other organ dysfunction; refuse to signature the informed consent