Comparison of microbiological yield from Bronchoalveolar Lavage Fluid (BALF) for the two common-used volume bronchoalveolar lavages(60ml and 120ml)in patients with different types of lower respiratory tract infection.

Assessment of the safety of two common-used volume bronchoalveolar lavages(60ml and 120ml), including the incidence of hospital-acquired pneumonia within 14 days after bronchoscopy, and other bronchoalveolar lavage related adverse events.

The morbidity and mortality of lower respiratory tract infection gradually increased in recent years, but the etiological diagnosis rate is still low. Quickly identifying the pathogenic bacteria and the corresponding antimicrobial therapy treatment is particularly important. Fibrotic bronchoscopy combined with bronchoalveolar lavage (BAL) has become a routine diagnostic tool for pulmonary infections in immunocompromised patients.

The correct operation of bronchoalveolar lavage and normalization of bronchoalveolar lavage fluid is a prerequisite for the exact results of the pathogen of BALF.

American Thoracic Society recommended amount of 100-300ml of saline solution was instilled into the distal bronchial tree in the diagnosis of interstitial lung diseases. But there is no standard of lavage fluid volume in the etiological diagnosis of lower respiratory tract infections, ranging from 60ml to 250ml ever reported in literature.

Less lavage volume would be more safer in patients with lower respiratory tract infections. The investigators hypothesize that microbiological yield would be no significant difference in patients with low volume （60ml) compared with large volume (120ml).

The purpose of this study is to explore a more effective and safer way of bronchoalveolar lavage in lower respiratory tract infection patients, and determine the pathogenic distribution among them.

Inclusion Criteria:

1. Clinical diagnosis of lower respiratory infection
2. Indication for bronchoalveolar lavage.

Exclusion Criteria:

1. Noninfectious pulmonary infiltration
2. Contraindication of bronchoscopy： Severe heart or pulmonary dysfunction Recent occurrence of myocardial infarction unstable angina pectoris Severe coagulation disorders (DIC), Massive hemoptysis Gastrointestinal bleeding Thrombocytopenia (<50*109/L) Severe superior vena cava obstruction syndrome Aortic aneurysm Multiple pulmonary bulla Extreme exhaustion
3. Diagnosed or highly suspected of tuberculosis infection
4. Researchers think that can not be entered into the group.