The Classification of Difficult Weaning and the Predictive Value of Relative Factors for Difficult Weaning

108 patients who passed the spontaneous breathing test (SBT) were included in this study,every patient were performed 30-60 minutes SBT after enrollment.Patients were divided into succeed weaning and difficult weaning group according the results of SBT, the difficult weaning group were futher divided into A(Airway and Lung dysfunction),B（Brain dysfunction）,C（Cardic dysfunction）,D（Diaphragm dysfunction）,E（Endocrine and metabolic dysfunction）five different groups according to the causes of difficult weaning. The respiratory mechanical parameters,the diameter of inferior vena cava and the diaphgram excursion were recorded before SBT and 30 minutes after SBT.