Infection and trauma take a important role in the acute respiratory failure.There are different causes and degrees of inflammatory reaction in the critically ill patient. The inflammatory reaction should also affect patients on mechanical ventilation dependence with body physiological response and disease prognosis in patients. Therefore, the investigators hypothesize that inflammation may have an important role in the prediction of weaning from mechanical ventilation.

In the process of mechanical ventilation, the patients were divided into two groups according to the failure of spontaneous breathing test and spontaneous breathing test.In the index of predicting mechanical ventilation, the investigators will take the index of inflammatory response, the function index of diaphragm and the amount of exhaled CO2 into account to reduce the failure rate of mechanical ventilation.

Inclusion Criteria:

• oral, nasal tracheal intubation and mechanical ventilation in patients with respiratory failure
• mechanical ventilation time over than 48 hours
• Glasgow score greater more than or equal to 13 points

Exclusion Criteria:

• Aged less than 14 years or more than 80 years old
• patients with neuromuscular disease
• pure heart failure pulmonary edema patients
• patients with tracheotomy

The patient with oral or nasal tracheal intubation and mechanical ventilation in respiratory failure