Inclusion criteria: Patients more than 45 years-old, were admitted due to COPD exacerbation.  COPD exacerbation criteria:  acute worsening respiratory symptoms without any other causes, And Smoking more than 15 pack-years or the history of noxious gas exposure, And Spirometry reports suggests obstructive ventilatory defect (FEV1/FVC <0.7) or Attending physicians diagnose as COPD by clinical parameters if spirometry data are not available while enrolling.  Definite COPD exacerbation: fulfill 1、2、3 Probable COPD exacerbation: fulfill 1、2、4  Exclusion criteria:  Significant fluid retention such as edema, pleural effusion or ascites, Patients with permanent pacemaker or implantable cardioverter defibrillator , Morbid obesity with BMI >34